Neutron Scattering at FRJ-2

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Neutron Scattering at FRJ-2

Experimental Reports 2003

Editors: T. Brückel, D. Richter, H. Tietze-Jaensch, R. Zorn

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Persistent Identifier: urn:nbn:0001-00185

http://nbn-resolving.de/urn/resolver.pl?urn=urn:nbn:0001-00185 Published by Forschungszentrum Jülich GmbH

D-52425 Jülich, Germany Phone: +49 2461 61-0

Editors: T. Brückel, D. Richter, H. Tietze-Jaensch, R. Zorn

Forschungszentrum Jülich does not accept any responsibility for loss or damage arising from

the use of information contained in this report. Reproduction including extracts is permitted

subject to crediting the source.

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Summary

The Research Centre FZ-Jülich is offering its neutron research facilities to a growing national and international user community for the benefit of their research using neutron beams. FZ- Jülich operates a 23 MW DIDO reactor that delivers a total neutron flux of 2.2 u 10

¹⁴

n/cm²s for a comprehensive suite of 15 instruments installed at 5 individual thermal beam tubes and, in addition, 5 external cold neutron guides. And there are more instruments to come.

In the year 2003 the reactor was in operation for 195 days and we are happy to announce that more than 110 individual experiments (constituting 55 % of the total) were carried out by a large external user community from 59 institutions all over the world. In close collaboration with internal staff the study of soft matter systems took the largest stake. The number of neutron experiments in biology and life science was vastly increasing to roughly fourth in place on the list of topics. Moreover, subjects of inelastic scattering, magnetism and engineering were among the other main topics of the experimental programme.

We gratefully acknowledge the EU funding programme “Jülich Neutrons for Europe” that enables numerous external users from the EU and associated countries to come over, visit Jülich and perform their experiments.

This booklet comprises the scientific reports of the experiments completed in 2003. We wish

to thank all external users, local applicants and instrument responsibles for their joint efforts

and contributions to the success and progress of the Jülich Neutron Research Facility.

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1

Thermal Neutron Experiments ...

5 Twin Diffractometer (SV-7) ... 5

Neutron Diffractometer (SV-28) ... 49

Time-of-Flight Spectrometer (SV-29) ... 59

Triple-Axis Spectrometer (UNIDAS) ... 81

Cold Neutron Experiments ... 93

E-Nuclear Magnetic Resonance ... 93

High Resolution Backscattering Spectrometer (BSS) ... 97

Double Crystal Diffractometer (DKD) ... 119

Time-of-Flight Spectrometer for Diffuse Neutron Scattering (DNS) ... 123

Neutron Reflectometer (HADAS) ... 137

Small Angle Neutron Scattering (KWS-1) ... 159

Small Angle Neutron Scattering (KWS-2) ... 225

Ultra Small Angle Neutron Scattering (KWS-3) ... 289

Neutron Spin Echo Spectrometer (NSE) ... 303

Publications

... 325

Neutron Instruments and Methods ... 327

Crystallography ... 334

Excitations ... 337

Magnetism ... 341

Soft Condensed Matter, Liquids, Glasses ... 351

Transport Processes ... 370

Biology ... 371

Geology, Archaeology ... 372

Materials Science, Engineering ... 375

Reactor ... 377

Theses ... 378

Training ... 381

User Access

... 385

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Introduction

With the FRJ-2 research reactor and the ELLA external neutron guide laboratory, the Research Centre Jülich (FZJ) is operating a powerful neutron source with a special priority in the field of cold neutrons. At a thermal power of 23 MW, the FRJ-2 reaches a maximum thermal neutron flux of 2.2

u 10¹⁴

neutrons/cm

²

s in the heavy water moderator. The liquid hydrogen cold source is located close to the reactor’s flux maximum and three neutron guides supply the instruments at the ELLA external neutron guide laboratory with cold neutrons of 2–15 Å wavelength. As a member of the German Helmholtz Association FZJ is committed to open its research facilities to scientists from Germany, Europe and across the globe for the benefit of their scientific research goals. The FZJ gratefully acknowledges complementary funding support from the EU that helps to fulfil our goals, namely providing large-scale research equipment for a wide range of scientific applications in the university and non- university sector far beyond the Research Centre itself.

The total number of reactor operation days was 195 days in the year 2003, again exceeding all equivalent numbers of the years before since the re-commissioning of the reactor in 1996. A total of 200 individual experiments was completed in 2003. The number exceeds slightly that of the last year (2002: 196). 55 % of all experiments were performed on the request of external and international users. Fig. 1 shows the number chart of the experiments per instrument. As in the years before, small-angle scattering (KWS-1/2 and the ultra-SANS KWS-3) took the largest load with all three instruments now running. The next popular instruments were powder diffraction (SV-7), closely followed by “inelastic work horses”, such as the spin-echo (NSE), the BSS back-scattering machine and the polarised neutron reflectometer HADAS.

0 5 10 15 20 25 30 35 40 45 50

BSS DKD DNS HAD

AS KW

S-1 KW

S-2 KW

S-3 NSE

SV- 7

SV28 SV- 29

UNIDAS Instrument Name

Number

FZJ intern FZJ extern

Figure 1: Experiments performed in the year 2003 on the neutron scattering instruments at FRJ-2

Scientific diversity was similar as to the years before, with most experiments devoted to soft

matter research, structure investigation and magnetism. Fig. 2 shows the scientific field

diversity of the experiments carried out at FRJ-2 averaged over the past 3 years. Noteworthy

is to mark that the remarkable increase in the number of biology oriented experiments, in

2003 the biology fraction achieved 10 % of the total number rather than 2 % in 2002 and

negligible values in the years before.

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Figure 2: Average science diversity of FRJ-2 experiments (1999–2003)

Figure 3: Geographical pattern of FRJ-2 users and type of their home institution according to the number of experiments in the years 1999–2003

In the past five years researchers from outside the Forschungszentrum Jülich carried out more than 50 % of the experiments. Fig. 3 shows the geographical and institutional distribution of the user groups visiting Jülich. The largest number comes from universities. This stresses the importance of the FRJ-2 facility in the academic community and across the European landscape of neutron sources. 15 countries are represented of which nine do not have their own national neutron scattering installations. In order to provide the increased number of external users with optimal support during their experiments a dedicated User Office has been founded in 2002. Details about its work and the user access possibilities are summarised at the end of this report.

It should be mentioned that in the year 2003 again financial support for non-German European users was possible by the European Union Transnational Access to Infrastructure project “Jülich Neutrons for Europe” (HPRI-2001-00175). Proposals accepted under this programme benefit from funding by the European Commission (travel expenses for users). Of course, the already existing support for German university users is continued. A contractual minimum of 133 instrument-days has to be allocated to this programme. Because of the exceeding demand of 332 days in 2003 and the high quality of most of the proposals experiments for a larger time (217 days in 2003) were accepted.

In 2003 several instrumental developments have opened new experimental possibilities, among them

We have developed a new method for full vector polarization analysis on the DNS, a

multi-detector time-of-flight spectrometer. The method uses an initially precessing polarization, so that finally non-precessing polarized intensities can be measured

Soft Matter 37%

Structure 20%

Technical 13%

Magnetism 12%

Biology Tunneling 4%

4%

Phonons 5%

Humanities

3% Diffusion 2%

D 48%

US 8%

F E 7%

5%

I 4%

other Europe 24%

Oversea

4% _{Nat Uni}

32%

Internat Uni 26%

Nat Lab 12%

Internat Lab 24%

Industry 6%

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simultaneously for all scattering angles and energy transfers. No additional devices are required, neither cryogenics nor zero-field requirements.

The new high resolution small angle scattering camera KWS-3 with focussing mirror is

now fully operation with a world-unique momentum space resolution down to 2

u 10⁴

Å

¹

can be achieved. Further developments on KWS-3 in 2003 were focussed mainly on sample position and environment, e.g.:

A set of large Quartz sample cells with varying path length (2, 1, 0.5 mm) was constructed to exploit the large beam size of 100u20 mm at sample position in order to achieve maximum intensity.

A

x,y-movable sample changer (3 positions) was installed, to allow automation of

experiments.

All connections into the sample chamber have been made vacuum tight, so that we can now do experiments with evacuated sample chamber, which increases the intensity and lowers the background due to suppression of air scattering.

In addition the instrument software was improved to facilitate alignment and control of the instrument.

The new thermal three-axis spectrometer SV30 is under construction.

The full refurbishment of the small angle scattering instruments KWS-1 was completed.

New electronics and a new detector for KWS-1 are in operation, now.

In addition to the instruments in Jülich the Institutes of Neutron Scattering and Scattering Methods operate and co-operate instruments at Institut Laue-Langevin (Grenoble, France) namely the triple-axis spectrometer IN12 and the NSE spectrometer IN15. Their respective experimental reports are included in the ILL documentation. The institutes also conduct the construction of new external instruments, a backscattering spectrometer for the research reactor FRM-2 in Munich and a neutron spin echo spectrometer for the spallation source SNS (Oak Ridge, USA).

Finally, in 2003 the 7

^th

International Neutron Laboratory Course took place in Jülich. This training course for students was again supported by the European Neutron Round Table. As in previous years the number of applicants (about 100) surpassed largely the available places.

Among the 50 selected participants 20 came from outside Germany.

This document comprises the experimental reports from experiments carried out at FRJ-2 in the year 2003 and publications of the past five years that are related to FRJ-2 experiments.

The reports are grouped by instrument

¹

and preceded by a tabular description of the instrument parameters. Detailed descriptions of the instruments can be found in the instrument handbook “Neutron Scattering Experiments at the Research Reactor in Jülich” or the web site www.neutronscattering.de .

Reiner Zorn and Holger Tietze-Jaensch

1 The SANS proposals are labelled by the instrument they originally applied for. Some experiments were transferred between KWS-1 and KWS-2 because of better feasibility or availability. The instruments SV-30, EKN, LAP-ND are not represented here because they are under construction, only used for test purposes, or not demanded during 2003. Nevertheless, their specifications can be found in the instruments handbook and on the web site.

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Twin Diffractometer (SV7)

Instrument Parameters

Monochromators - standard:

- optional:

Ni (220), PG (002)

Ni (200), Cu (111), Pb (311), Ge (111)/(311) Monochromator angles: 52° and 40°

Wavelengths: 1.0 Å d Od2.3 Å

Collimators - primary beam:

- scattered beam (optional):

Soller: 12 min radially oscillating

Max. beam size: 25u 40 mm²

Mean sample volume (cylinder): 10 mm , 30 mm high Scattering region: 0°d24 d90°

Detectors: linear JULIOS units

Max. neutron flux at sample: 10⁶ n/cm² s

d-spacings: 0.7 Å ddd35 Å

Mean resolution 'd/d: 10²

Sample environment:

Closed cycle He-cryostat: 4 ... 293 K; He-bath cryostat:

1.5 ... 4.2 K; He-3 cryostat: 0.3 ... 293 K; Split coil magnet cryostat: 0 ... 7 T, 4 … 293 K; cryofurnace 4 ... 400 K; Full circle goniometer with external Z-rotation: 293 K; Flow cryostat containing full circle goniometer: 4 ... 293 K

Instrument Responsible

Dr. Wolfgang Schäfer Tel. +49-(0)2461-61-6024 Email: w.schaefer@fz-juelich.de DP Ekkehard Jansen Tel. +49-(0)2461-61-4054 Email: e.jansen@fz-juelich.de

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Institut für Festkörperforschung Forschungszentrum Jülich GmbH D-52425 Jülich

Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Proposal number: SV7-01-013

Experiment title:

Critical magnetic behaviour for integer and half-integer spin quantum numbers

Dates of experiment: December 2003 Date of report: 09 February 2004

Experimental team:

Names Addresses

U. Köbler E. Jansen W. Schäfer

IFF FZ-Jülich

IFF FZ-Jülich und Inst. f. Mineralogie und Petrographie Uni Bonn IFF FZ-Jülich und Inst. f. Mineralogie und Petrographie Uni Bonn

Local Contact: W. Schäfer Experimental report text body

Absolute zero of temperature, T=0, and the critical temperature, Tc, are to singular points. In the vicinity of singular points simple power functions with universal exponents hold for many physical quantities. This is well known for the critical range but it seems to be correct also for To0 [1]. In extensive studies of transition metal compounds with a quenched orbital moment and a well defined spin quantum number the universal exponents H for the order parameter for To0 could be established experimentally [2]. Surprisingly, these exponents depend on whether the spin quantum number is integer or half-integer. Classical spin wave theory is not able to explain this [3]. Moreover, the power functions of Table 1 are not first order approximations but hold over a large temperature range, normally up to the critical range at about 0.85Tc where the crossover to the critical power function with exponent E occurs. As a consequence, the two exponents H and E give a complete description of the spontaneous magnetization. Table 1 reproduces the empirical power functions T^H of the order parameter for To0.

3D 2D 3D anisotropic

1D 2D anisotropic

exchange interactions

2 5 2 3 2

9

T T

T³ T²

T² T

half - integer spin integer spin

Table 1

Form Version: 19.02.03 1

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The question now is, whether the exponents H for To0 and the exponents E for ToTc are correlated, i. e.

whether a similar universality scheme as in Table 1 exists also for the exponents E. Since the experimental evaluation of the H values is much more convenient than evaluation of the E values the dependence of E on the dimensionality of the relevant interactions is not clear up to now. In particular, it is not generally known that in three-dimensional magnets the critical exponent E is also spin dependent: for magnets with an integer spin E is essentially of the Heisenberg type but for half-integer spins it is of the mean field type. Table 2 compiles the proposed scheme of E values together with the exponents J for the susceptibility and G for the critical isotherm.

The proposed systematic of the exponents E in Table 2 is empirical and requires further experimental verifications. To this end we have performed neutron scattering measurements on a FeWO4 powder sample.

Due to the Fe²⁺ ion the spin is S=2. In Fig. 1 we have plotted the sublattice magnetization of FeWO₄ to the power of 1/E=2.75 on a linear temperature scale. Note that we have chosen E =4/11=0.3636… as the Heisenberg value. It can be seen that a straight line results in Fig. 1, i.e. the Heisenberg value forE is confirmed which conforms to Table 2.

This result is very remarkable in comparison to Mn_0.88Fe_0.12WO₄. In this material the Mn²⁺ ion with S=5/2 dominates and a mean field exponent of E=1/2 has been observed, which is also in agreement with Table 2 [5].

[1] J.A. Hertz, Phys. Rev. B 14 (1976) 1165.

[2] U. Köbler, A. Hoser, D. Hupfeld, Physica B 328 (2003) 276.

[3] F.J. Dyson, Phys. Rev. 102 (1956) 1230.

[4] we thank N. Stüsser of HMI-Berlin for the FeWO4 powder sample.

[5] Yongfan Ding, PhD Thesis (1999) HMI-Berlin.

4

G

19

G

15 3

G 14 3

J 4 J G ³

critical exponents

3 1 8 1

1 E 0.5

3D 2D1D

exchange interactions

4 5 4 7 11

4

J J E

E

half - integer spin integer spin

Table 2

68 70 72 74 76 78

0 200 400 600 800 1000 1200 1400 1600 1800 2000

M2.75 (a.u.)

T (K) FeWO₄ Fe²⁺: S=2

Fig. 1.

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Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Experiment title: The crystal structure of methyl iodide clathrate at T=4K Dates of experiment: 20.-23.1.2003 Date of report: 18.1.2004 Experimental team:

Names Addresses

M. Prager R. Skowronek

Forschungszentrum Jülich

Inst. F. Mineralogie, Universität Bonn

Local Contact: W. Schäfer

Experimental report text body

Clathrates are a fascinating class of materials: a framework of matrix molecules forms cages which allow to incorporate simple molecules in identical environments and thus experience the same matrix effect. Therefore spectral lines are usually rather sharp and contain clear information. The combination of different host and guest molecules allows a huge variety of clathrates to be produced. Water clathrates with water soluble guest molecules like tetrahydrofuran can be prepared easily. A recently grown interest concentrates on the methane clathrates [1] which are only stable in a certain pressure-temperature regime. This 'burnable ice' exists in nature and may form one of the largest energy reservoirs on earth.

From a fundamental point of view methane represents a prototype of a non polar guest molecule. CH3I is an interesting and different probe of the clathrate cages compared to methane because it interacts with the host surface via dipolar interaction. To incorporate this non water-soluble molecule to form the clathrate CH₃I x 17H₂O a special preparation technique [2] was developped. The system crystallizes in the cubic II structure. In this structure there are small and large cavities and only the equivalent large cages are filled by guest molecules. We have prepared new samples by this technique. The formation of the clathrate becomes evident by the transformation into a transition gel state and an increase of the melting point to T_m~4C. To be able to interpret results of planned spectroscopic experiments the crystal structure of the samples must be controlled.

Neutron diffraction was applied using SV7. The wavelength was Ȝ=1.09590Å. According to literature clathrates of the cubic II structure show lattice parameter of ~17.6Å, Z=8. The two samples investigated were transferred cold from the storage dewar into the Top-loader Orange cryostat and thereafter cooled to the required temperatures. Fig. 1 show a diffractogram. All observed Bragg peaks can be indexed within the cubic II structure. Lattice parameters of a=17.106Å for the fully deuterated material at T=6K and a=17.067(17.159)Å for a deuterated matrix with protonated guest molecules at sample temperatures T=6(200)K are found.

1

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Fig. 1 Diffractogram of CH₃I*17D₂O. Sample temperature T=6K. Miller indices characterize each peak.

The short wavelength used leads to overlapping lines. The later performed high resolution spectroscopic experiment at the NEAT spectrometer at HMI [3] delivered as a by-product the well resolved diffraction pattern for low momentum transfers corresponding to 2theta < 15^o in figure 1. It fully confirmed the interpretation based on the above data.

[1] C. Gutt, W. Press, A. Hüller, J. Tse, H. Casalta, J. Chem. Phys. 114,4160(2001) [2] C. Albayrak, Dissertation, Aachen 1988

[3] M. Prager, J. Pieper, A. Buchsteiner, A. Desmedt, Proceedings of the ECNS2003, to appear in Physica B

2

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Form Version: 19.02.03 1 Institut für Festkörperforschung

Forschungszentrum Jülich GmbH D-52425 Jülich

Experimental Report

of Neutron Scattering Experiments at the FRJ-2 Reactor

Experiment title: Experimentelle Bestimmung der Gleitsysteme von Hämatit bei Temperaturen über 400°C, (hier bei 600 und 700°C verformte Einkristalle)

Dates of experiment: 45 Tage in der Zeit vom 18.01.03 bis 28.07.03

Date of report: 03.02.2004

Experimental team:

Names Addresses H. Siemes *

B. Klingenberg (E.Rybacki) (M. Naumann) (K. Kunze)

Institut für Mineralogie und Lagerstättenlehre * Förderung DFG Si209/32-1 RWTH-Aachen, Bunsenstr. 8, 52056 Aachen

Geoforschungszentrum Potsdam, Projektbereich 3.2: Rheology and Tectonophysics Telegrafenberg D429,14474 Potsdam

Geologisches Institut, ETH Zentrum, EBSD-Labor CH-8092 Zürich

Local Contact: E. Jansen, Univ. Bonn Experimental report text body

Dieser Report erweitert und ergänzt den Report aus dem Jahre 2002: Proposalnummer SV7-02-005 Motivation

Experimentelle Bestimmungen der Gleitsysteme an Einkristallen von Hämatit unter definierten Bedingungen der Temperatur (25°C, 200°C, 400°C), Manteldruck (400 MPa) und Verformungsrate (~10^-5s^-1) und der Bestimmung der Zwillingspannungen bzw. kritischen Schubspannungen liegen bisher nur von Hennig-Michaeli

& Siemes (1982) [1] vor. In Verformungsversuchen an Einkristallen soll die Kenntnis der Gleitsysteme von Hämatit auf Temperaturen von 600°C bis 800°C ausgedehnt werden.

Ausgangsmaterial und Verformungsversuche

Als Ausgangsmaterial wurden natürliche Einkristalle von verschiedenen Fund- punkten in Minas Gerais, Brasilien verwendet. Diese Kristalle wurden orientiert geschnitten und zu prismatischen Probenkörpern von etwa 7 * 7 mm² Querschnitt und 13 mm Länge mit den Längsachsen A, B; C, D und M verarbeitet (Abb.1). Im Stauchversuch kann eine Zwillingsbildung nur eintreten, wenn diese zu einer Kürzung der Probe führt, und nur Gleitsysteme mit höheren Orientierungsfaktoren können aktiviert werden. Daher kann in der Orientierung A nur r-Zwillings- gleitung auftreten und in den Orientierungen D und M nur {a}<m>-Gleitung. In den anderen Orientierungen können {a}<m>- und (c)<a>-Gleitung, sowie die c- Zwillingsbildung aktiviert werden.. Die Versuche wurden in einer Paterson- Apparatur [2] ausgeführt.

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Form Version: 19.02.03 2 Neutronen-Texturmessungen und EBSD-Aufnahmen

An den in der folgenden Übersicht stehenden verformten und unverformten Proben wurden jeweils 5 Reflexe mit dem Texturgoniometer SV7 gemessen [3]

Versuche bei 600°C: Versuche bei 700°C: unverformte Proben:

A: H43C1 A (c) H43C3 A (c) H92C A (c) H52C1 A (c)

B: H91R A (r) --- H32R1, H32R2,H33R1 A (r) C: H93F1 A (f) H41F1 A (f) H41F2 A (f)

D: HP142 A (~a) HS230 A ( a) ---

M: H42M3 A (m) H42M2 A (m)

Hier wird beispielhaft über die Ergebnisse an der Probe H91R (Orientierung B in Abb. 1) berichtet

Abb. 3 gibt die fünf Polfiguren der Probe H91R wieder. Entsprechend der Orien- tierung der Stauchachse liegt im Zentrum der r-(012)-Polfigur ein Dichtemaxi- mum. Ein Teil der Maxima läßt sich einer r-Verzwillingung zuordnen, wie der Vergleich mit der Abb. 2 zeigt. Diese r-Zwillinge sind Wachstumszwillinge, die bereits vor der Verformung vorhanden waren. Einige Maxima sind jedoch der c-

Verzwillingung zuzuschreiben, die in Abb. 4 schematisch wiedergegeben ist. Die zugehörigen Bereiche in den Polfiguren der Abb. 3 sind durch rote Kreise markiert. Die EBSD-Aufnahmen [4] der Abb. 5 und 6 wurden in Flächen parallel zu den Oberflächen der prismatischen Proben aufgenommen. Neben den r-Zwillingen, die auch leicht im Polarisationsmikroskop zu erkennen sind, wird das Auftreten von c-Zwillingen (Abb. 5) bestätigt.

Außer den Zwillingen erkennt man noch linienförmige, schwache Orientierungskontraste, die als „Gleitlinien- spuren“ der Gleitsysteme {a}<m> (Abb. 5) und (c)<a> (Abb. 6) anzusprechen sind. In den Polfiguren der übrigen Orientierungen wurden neben den Wachstumszwillingen insbesondere noch „Gleitlinienspuren“ der {a}<m>-Gleitung aber auch Spuren gefunden, die noch nicht zugeordnet werden können.

Die Texturaufnahmen der unverformten Proben werden als Referenzmessungen zu den Texturaufnahmen der Proben nach der Verformung im Folgeprojekt benötigt. Diese Versuche werden zur Absicherung der bisherigen Ergebnisse und zur Kontrolle der früheren Untersuchungen [1] auch bei niedrigen Temperaturen ausgeführt.

Literaturangaben:

[1] Hennig-Michaeli, Ch. & Siemes, H.: In: High Pressure Research in Geoscience, Schweizer- bart'sche Verlagsbuchhandlung, Stuttgart (1982) 133-150.

[2] Paterson, M.S., 1990: In: The Brittle-Ductile Transition in Rocks. The Heard Volume American Geophysical Union Geophysical Monograph 56 (1990) 187-194.

[3] E. Jansen, W. Schäfer, A. Kirfel, J. Struct. Geol., 2000, 22, 1559-1564.

[4] K. Kunze, B.L. Adams in: H.J. Bunge, S.Siegesmund, W. Skrotzki, K. Weber (Eds.) Textures of Geological Materials, DGM-Informationsgesellschaft, 1994, 127-146.

Wir danken der Deutschen Forschungsgemeinschaft für die Mittel zur Durchführung des Projektes.

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Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Proposal number: SV7 – 03 - 002

Experiment title: Neutron Diffraction Study of KNO3 at elevated temperatures Dates of experiment: 7-16.04.2003

26-28.05.2003

Experimental team:

Names Addresses

Dr. N. Zotov Prof. A. Kirfel

Dr. W. Schäfer R. Skowornek

Mineralogisch-Petrologisches Institut, Universität Bonn Poppelsdorfer Schloß, D-53115 Bonn

MIN/ZFR (University of Bonn)

Local Contact: W. Schäfer Experimental report text body

KNO₃ exists in different modifications depending on temperature and pressure [1-2]. At ambient pressure, the orthorhombic D-phase transforms upon heating into the trigonal disordered E-phase at about 127ôC. This E- phase remains stable up to the melting temperature at about 325ôC. Upon cooling, an intermediate trigonal J- phase appears at about 120ôC, the stability field of which at ambient pressure depends on the thermal history and the cooling rate. The E- and the J-phases cannot be quenched and their structures were determined from in- situ powder X-ray diffraction data. Taking advantage of the strong scattering contrast between neutrons and X- rays in the case of KNO3 and using a newly developed furnace for the powder diffractometer SV7a we have obtained new results for the phase transition in KNO₃.

Diffraction patterns (O=1.096 Å) of 3 hours duration each were taken every 5-10ôC, both upon slow heating and cooling (0.167 ô/min). The temperature stability of the furnace was better than 0.2ôC. The temperatures measured with a NiNiCr thermocouple were calibrated against the well-known temperature dependence of the lattice parameter of NaCl. The lattice parameters of the D- and the E-phases (Fig. 2) were determined from Rietveld refinements using the FULPROF program. The room temperature cell parameters of the D-phase are in good agreement with literature values [3].

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The total diffraction data show: (i) the appearance of reflections of the J-phase at about 139ôC (marked with * on Fig. 1); (ii) co-existence of the E- and J-phases in the temperature range 139-122ôC upon cooling; (iii) co- existence of the D- and the E-phases in the temperature range 112-132ôC upon heating; (iv) anomalous behaviour of some reflections (e.g. 102) of the D-phase upon heating. In contrast, in-situ synchrotron X-ray diffraction experiments with very short measuring times of about 2 minutes did not reveal the simultaneous presence of the D- and E-phases.

16 18 20 22 24 26 28 30 32 34 0

1000 2000 3000 4000

* *

98 122 127 157^oC

133

Intensity (counts)

24 (degree)

40 80 120 160 200 240 280 320 360 5

6 7 8 9 10

c

b a

DE E-phase

D-phase

Temperature (^oC)

Lattice Parameters (A)

Fig. 1. Neutron diffraction patterns on cooling Fig. 2. Lattice parameters as a function of temperature The co-existence of the D- and E-phases over a 20^oC temperature interval as well as of the E- and J-phases over at least 15^oC interval as found in the present experiments with very long measuring times and slow heating/cooling rates indicates that the respective phase transitions are sluggish and probably of second order.

The temperature dependence of the intensity of the (101) reflection of the D-phase was used to determine the critical exponent of the order parameter of the D o E transition. Despite some intensity irregularities the data could be fitted with the expression I=Io_W_^2E, where Io is a constant, W the reduced temperatureW = 1-T/Tc,Tc the phase transition temperature and E the critical exponent. A phase transition temperature T_c = 134(2)^oC and a critical exponent E=0.30(5) yield the best fit to the data. The latter value supports the second-order character of theD o E transition. Detailed discussion of the results is given in Ref. [3].

0.0 0.2 0.4 0.6 0.8

0 1000 2000 3000 4000

(101)_D Fit E = 0.30(5)

Intensity (counts)

(T_c - T)/T_c

Fig. 3. Temperature dependence of the (101)D reflection upon heating.

[1] E. Rapaport and G.C. Kennedy, J. Phys. Chem. Solids 26 (1965) 1995 [2] J.K. Nimmo and B.W. Lucas, Acta Cryst. 29 (1966) 265

[3] H.E. Swanson et al., Nat. Bureau of Standards Circular No 539, Vol. III (1954) 58 [3] A. Kirfel, N. Zotov and W. Schäfer, Physica B (2004), in press

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Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Experiment title: Magnetic order of RNi4Al (R = Tb, Dy) compounds studied by neutron diffraction

Dates of experiment: 15. Feb. – 10. Mar. 2003 12. Sep. – 16. Sep. 2003

Date of report: 28. Jan. 2004

Experimental team:

Names Addresses

T. ToliĔski (A. Kowalczyk)

R. Skowronek

Institute of Molecular Physics Polish Academy of Sciences Smoluchowskiego 17 60-179 PoznaĔ, Poland MIN/ZFR (Univ. of Bonn)

Local Contact: W. Schäfer, Univ. of Bonn Experimental report text body

Apart from a basic scientific interest the RNi4Al and RNi4B compounds (R = Y or rare earth) have been widely investigated due to the possible and partly realized commercial applications. The RNi₄B compounds crystallize in the CeCo₄B-type structure, whereas RNi₄Al in the structure of CaCu₅. Both RNi₄B and RNi₄Al are described in the point group P6/mmm. The difference between these structures results from the way of locating of the B and the Al atoms in the lattice sites. B substitutes Ni in every second plane (2d sites), whereas Al is statistically distributed in the 3g sites of Ni [1].

The RNi₄B compounds have shown interesting anisotropic properties, especially for R = Sm having large coercive field (7 T). The YNi₄B compound revealed a presence of a superconducting phase and RNi₄B for R = Ce, Nd and Pr exhibited mixed valence properties.

In our neutron diffraction studies we concentrated on the magnetic properties of RNi4Al to get rid of the problem of the large absorption of natural boron. We have studied TbNi₄Al and DyNi₄Al. The studies have been performed employing neutron diffraction yielding both structural and magnetic information. The magnetic characterization has been supported by the measurements of the temperature dependence of the ac and dc magnetic susceptibility and field dependence of the magnetization. The obtained results are compared with the magnetometric studies of the B-based counterparts, i.e., TbNi4B and DyNi4B compounds [2,3].

In 2003 the neutron diffraction experiments were performed on SV7 instrument [4]. The neutron wavelength was 1.096 Å. The sample was contained in a cylindrical vanadium can mounted (1) in a refrigerator cryostat and (2) in a cryomagnet with external magnetic fields up to 5 T perpendicular to the horizontal diffraction plane. Neutron diffraction results were analyzed by full-pattern Rietveld refinements using FULLPROF. The standard deviation of refinement was about 2%.

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Results [4]:

1. The unit cell volume of the Al-based compounds is reduced by about 43% in comparison with the B-based compounds.

2. The magnetic moments and ordering temperatures (Fig. 1) extracted from the neutron diffraction experiment and magnetometry are in good agreement. This consistency of the magnetic moments is indicative of a negligible contribution of the Ni atoms to the magnetic properties of RNi₄Al.

3. The magnetic moments and ordering temperatures of RNi₄Al compounds are reduced in respect to the RNi₄B counterparts.

4. DyNi4Al shows long-range order in the hexagonal basis plane but for TbNi4Al also a presence of a short- range order is revealed (Fig. 2).

c)

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Fig. 1. Magnetic susceptibility (a), (b) and the sum of all integrated neutron magnetic intensities (c), (d) as a function of temperature for TbNi₄Aland DyNi₄Al revealing T_C = 23 K and 11 K, respectively.

T=4.2K

10 15 20 25

0 1 2 3

4 T=293K

10 15 20 25

0 1 2 3

4 4.2K - 293K

10 15 20 25

0 1 2 3

Intensity(arb. units)

2T (deg)

Fig. 2. Comparison of the low-angle parts of the diffraction patterns at 4.2 K (left) and 293 K (center) and of the temperature difference pattern containing only magnetic scattering contributions (right) for TbNi₄Al. Broad background modulations of diffuse magnetic scattering are visible at 4.2 K and in the difference pattern indicating a contribution of magnetic short-range order.

References:

[1] T. ToliĔski, W. Schäfer, W. Kockelmann, A. Kowalczyk and A. Hoser, Phys. Rev. B 68, 144403 (2003).

[2] T. ToliĔski, A. Kowalczyk, A. Szlaferek, B. Andrzejewski, J. Kovac and M. Timko, J. Alloys Compd.347, 31 (2002).

[3] T.ToliĔski, A.Kowalczyk, A.Szlaferek, M.Timko, J.Kovac, Solid State Commun.122, 363 (2002).

[4] T. ToliĔski, W. Schäfer, A. Kowalczyk, B. Andrzejewski, A. Hoser, A. Szlaferek, Magnetic properties of TbNi4Al and DyNi4Al compounds: investigation via neutron diffraction and magnetometry, submitted for publication.

Fig. 3. The crystallographic structure of RNi₄Al compounds.

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Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Experiment title: Polyphase deformation of quartzitic mylonites of the Monte Rosa nappe (Piemonte, Italy)

Dates of experiment: 20 days between 13/03/03 and 25/06/03

Experimental team:

Names Addresses J. Pleuger

N. Froitzheim

Geologisches Institut Universität Bonn Nussallee 8 D-53115 Bonn

Local Contact: E. Jansen, Universität Bonn

Within this project twelve samples of mylonitic quartzites from the southern margin of the Monte Rosa nappe have been analyzed. Six of them were collected southeast of the Monte Rosa mountain in the upper part of the Sesia valley (fig.1). Here, the continental Monte Rosa rocks and overlying ophiolitic units are affected by a large south-vergent fold (called Cimalegna fold herein) that locally brings the Monte Rosa gneisses on top of the ophiolites. The ophiolitic rocks in the lower limb of the Cimalegna fold themselves form two large fold structures whose geometry precludes that they are parasitic structures of the Cimalegna fold. Thus, a detailed structural analysis was necessary to recognize the complete fold geometry (fig.2).

fig.1: Tectonic map of the Monte Rosa nappe, white rectangle

marks the study area in the upper Sesia valley fig.2: Schematic drawing of the fold geometry in the upper Sesia valley

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Form Version: 19.02.03 2 The triclinic quartzite textures are interpreted in terms of the rotation of pre-existent textures during subsequent deformation phases whose shear sense can be determined. This, in combination with geological field data, proved to be useful in unravelling the deformation history of the rocks in that three main deformation phases can be distinguished: Top-to-the-north/northwest directed movements attributed to the principal stages of nappe emplacement (D1) were followed by top-to-the-southwest shearing (D2) that in turn is postdated by top-to-the- eastsoutheast shearing (D3). The last two phases were accompanied by repeated folding and led to the formation of the Cimalegna fold (D3) and the two north-closing anticlines below (D2).

As examples, two of the textures shall be briefly addressed: Looking at sample MR8 the stronger maximum of the c-axis pole figure lies between the centre and the periphery in the lower half of the hemisphere and is rotated from the vertical direction in a clockwise sense. Accordingly, the {a} pole figure yields three maxima on a great circle around the {c} maximum. The strongest a maximum is on the periphery of the diagram. Both the asymmetries of the {a}and the {c} pole figures indicate dextral sense of shear which is geographically north vergent (D1), but the triclinic symmetry of the pole figures is probably best explained by a later overprint.

MR48 yields a single girdle distribution of {c} that contains a maximum in a similar position as in MR8. The fact that the c-axis girdle does not meet the middle of the projection means that the shear direction (southeast, D3) documented by the quartz texture trends about 25⁰ more to the south than the stretching lineation.

Six more analyzed samples were collected from the tail-shaped eastern continuation of the Monte Rosa nappe north of the Insubric line. When their textures are interpreted, they shall be compared with those of the Sesia valley in order to enhance our knowledge about the kinematics of the Monte Rosa nappe, especially its exhumation.

fig.3: Pole figures of four samples from the upper Sesia valley. (110) and (100) are experimental, (001) is calculated from the ODF

fig.4: Pole figures of four samples from the tail-shaped eastern continuation of the Monte Rosa nappe. (110) and (100) are experimental, (001) is calculated from the ODF.

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Experimental Report

of Neutron Scattering Experiments at the FRJ-2 Reactor

Experiment title: High and low temperature neutron powder diffraction on magnetic ThMn12-type compounds YFe12-xMox and TbFe12-xMox

Dates of experiment: March and december 2003. Date of report:

26/02/04 Experimental team:

Names Addresses

R. Hermann F. Grandjean G.J. Long R. Skowronek

Département de Physique – Bat B5 Université de Liège

B-4000 LIEGE BELGIQUE

MIN/ZFR (Univ. of Bonn)

Local Contact: W. Schäfer, Univ. of Bonn Experimental report text body

Motivation

A large variety of binary and ternary intermetallic compounds AB12

and AB12-xCx, respectively, crystallize in the tetragonal ThMn12 - type structure (Fig. 1). This structure is characterized by 2a sites occupied by the A atom and three non-equivalent sites 8f, 8i and 8j to accommodate the B and C atoms according to special site prefer- ences. Members of a subgroup of this family of intermetallics with A being a rare earth (R) and B being the 3d transition element Fe are of special interest in view of their potential use as permanent magnets. R-Fe intermetallics are assumed to combine strong magnetization anisotropy and high Curie temperatures which are associated with the rare earth ions and high iron concentrations, respectively. Binary RFe12 compounds, however, do not exist. The ThMn12 structure has to be stabilized by an additional element C, e.g. Mo to form RFe12-xMox compounds.

This project represents a continuation of projects SV7-02-002 and SV7-02-012 (see the previous Experimental Reports) which was restricted to a measuring time of 5 and 8 days spent for the series of YFe12-xMox and TbFe12-xMoxcompounds at room temperature.

This document reports the neutron diffraction measurements of some of those compounds at 4.2 K and 823 K.

1 Fig. 1: ThMn12-type structure:

tetragonal unit cell and sublattices

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Experimental

We have recently undertaken detailed iron-57 Mössbauer spectral studies of the RFe12-xMox compounds, where R is Y and Tb, and 0<x 3. The obtained Mössbauer spectra are very complex because the iron atoms occupy three different crystallographic sites, the 8f, 8i, and 8j sites, and have a distribution of near-neighbor environments due to the partial occupation of one or more of these three crystallographic sites by molybdenum.

The analysis of these spectra is greatly facilitated and much more meaningful if the specific Mo site occupancies and the orientation of the iron and rare-earth magnetic moments are known from powder neutron diffraction studies.

Within this project the diffraction patterns of TbFe10.5Mo1.5, YFe10.8Mo1.2 and YFe11.5Mo0.5 have been measured, see Fig. 2, at T = 823 K and the patterns of YFe12-xMox with x = 0.5, 1.2, 3.0 have been measured at T = 4 K using a wavelength of 1.096 Å on SV7. A detailed analysis of these patterns through Rietveld refinements is in progress.

Experimental Data

YFe11.5Mo0.5 YFe11.5Mo0.5

YFe11Mo YFe10.8Mo1.2

YFe9Mo3 TbFe10.5Mo1.5

2

0 2 4 6

10 20 30 40 50 60 70 80

Neutron counts, ×103

Angle, 2θ^o

YFe11Mo T=3.6K Hermann, Luettich n3131316/M6M6M131

2 theta

20 40 60 80

intensity / 103

0 1 2 3 4

YFe9Mo3 T=3.6K Hermann, Luettich n3142131/M6M6M131

2 theta

20 40 60 80

intensity / 103

0 1 2 3 4

0 2 4

10 20 30 40 50 60 70 80

Angle, 2θ^o

0 2 4

10 20 30 40 50 60 70 80

Angle, 2θ^o

0 2 4 6 8

10 20 30 40 50 60 70 80

Angle, 2θ^o

Fig. 2: The neutron diffraction patterns of the indicated compounds measured at 4 K, left, and 873 K, right.

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Experimental Report

of Neutron Scattering Experiments at the FRJ-2 Reactor

Experiment title: Neutron Texture Analysis of Omphacites in Eclogites Dates of experiment: 10. September –

18. September 2003

Date of report: 15. December 2003

Experimental team:

Names Addresses Dr. Walter Kurz

Dr. Wolfgang Unzog Dr. Nikolaus

Froitzheim Jan Pleuger Rene Hundenborn

Institut für Technische Geologie und Angewandte Mineralogie, Technische Universität Graz, Rechbauerstr. 12, A- 8010 Graz.

Institut für Geologie und Paläontologie,

Universität Graz, Heinrichstr. 26, A- 8010 Graz.

Geologisches Institut, Universität Bonn, Nussallee 8, D- 53115 Bonn.

Local Contact: Dr. Wolfgang Schäfer, Ekkehard Jansen Experimental report text body

Microstructures and Crystallographic Preferred Orientations (CPOs, textures) of omphacite within eclogites from distinct (ultra-) high-pressure units of the Alps were analyzed in order to constrain the deformation conditions during and after high-pressure metamorphism.

Microstructures and Crystallographic Preferred Orientations (CPOs, textures) of omphacite within eclogites from distinct (ultra-) high-pressure units of the Alps, in particular the Koralm-Complex, were analyzed in order to constrain the deformation conditions during and after high-pressure metamorphism. To confirm the results from previous studies, additional samples from several units were analyzed. The omphacite CPOs bear significant details for the reconstruction of the deformational evolution of several units. CPOs from the Austroalpine Koralm-Saualm Complex (Fig. 1) (WK20-97, WK51-97, WK17-98a, WK3-99, WK7-97, WK8- 97; WK2-03, WK3-03, WK4-03, WK6-03, WK8-03, WK10-03, WK11-03) correspond to S- type fabrics (with a girdle distribution of c {001} within the X-Y- plane, and b {010} clusters near Z), related to a deformation geometry within the flattening field. This geometry is documented by the shape fabrics too.

Textures described from the Dora Maira Massif show L>S- and L- type CPO fabrics, indicating a plane strain to constrictional deformation geometry. The CPOs from the Adula Nappe (Fig. 1) (WK147-01, WK151-01, WK153-01, WK154-01, R54, R56, B14, WK159-01, WK160-01, WK144-01; WKAD1-02) may all be

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Form Version: 19.02.03 2 described in terms of very well developed L- type fabrics (with c {001} clusters near Z, and a girdle distribution of b {010} axes within the Y-Z- plane) formed within the constrictional field. Constrictional strain (axial elongation) is interpreted to have started at the peak of high-pressure metamorphic conditions and was continued along the retrograde path. Omphacite CPOs from the Eclogite Zone of the Tauern Window (Fig. 1) (WKOA01-1; WKOA01-4, WK109-97, WK108-97, WK46-98, WK50-98, WK48-98, WK110-97, WK526, WK527) show a continuous transition from S- to L- type fabrics, corresponding to the transition from coarse- grained eclogites to fine-grained eclogite mylonites. This evolution is related to the final phases of the prograde evolution unit and coincides with a transition from a flattening to a constrictional deformation geometry. This is indicated by the shape fabrics, too. The constrictional geometry prevailed along the retrograde section of the PT path.

The evolution of microstructures and CPOs is assumed to correlate with the deformation geometry, which is directly linked with the mechanisms of exhumation. S- type fabrics predominantely occur within eclogites exhumed by crustal extension, in particular the Koralm-Saualm Complex. L>S- and L- type fabrics predominantely occur within eclogites exhumed by extrusion within a low-angle corner (“subduction channel”), in particular the Dora Maira Massif, the Adula nappe, and the Eclogite Zone. S- type CPOs from the Eclogite Zone were formed along the prograde path and are assumed to indicate compressional deformation related to the burial of this unit.

Fig. 1. Representative omphacite cyrstallographic preferred orientations from the Koralm Complex (WK2-03), the Adula Nappe (WKAD1-02) and the Eclogite Zone (WKOA4-01).

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Experimental Report of Neutron Scattering Experiments

at the FRJ-2 Reactor

Experiment title: Crystal-structure of NaNaMgMg5Si8O22(OH)2, a synthetic P21/m amphibole Dates of experiment: 28 Jul-01Aug 2003 Date of report: 20 Jan 2004

Experimental team:

Names Addresses

Dr Gatta G.D. (1) Dr Iezzi G. (1) Prof. Rinaldi R. (2) Prof. Della Ventura G.

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(1) Bayerisches Geoinstitut – Universitaet Bayreuth - Germany (2) Dip. Scienze della Terra- Universitá di Perugia - Italy

(3) Dip. Scienze di Scienze Geologiche- Universitá di Roma-3 - Italy

Local Contact: Dr. Wolfgang Schäfer

Amphiboles are among the most important OH-bearing silicate minerals with the hydroxyl ion as an essential constituent of their structure and a very large P-T stability field (in a hydrous environment) which is due to their structural complexity. In fact the double chain-silicate (Fig. 1) is capable of incorporating most, if not all, major elements of the Earth (except C and S). However the hydrogen content and distribution within the amphibole structure is one of the major problems in the crystal chemistry of amphiboles. The compound

ANa1B

Na1Mg1C

Mg5Si8O22(OH)2 is a model clino-amphibole composition not yet found in Nature. Clino- amphiboles may crystallise in two space groups, C2/m and P2₁/m, as a function of composition and/or P-T parameters. Several HT and HP studies on the Mg-cummingtonites have demonstrated the displacive phase- transition mechanisms between P- and C-polymorphs. ^ANa1B

Na1Mg1C

Mg5Si8O22(OH)2 amphibole (Space Group:P2₁/m at room-T,Iezzi et al., 2004) is of particular interest due to the presence of ^ANa and ^BNa₁^BMg_1, which affect the HT-P2₁/m–C2/m phase transition (Càmara et al., 2003). The LT neutron diffraction study was undertaken to check the existence of a possible phase transition, to sharply locate the two H positions and to obtain accurate measurements of the two O-H bond lengths.

About 1,5g of oxides mixture were utilised for the synthesis in an IHPV apparatus, at 850°C and 0.3GPa, with 20wt% (H,D)2O. EPMA, IR and single-crystal X-ray diffraction yielded the composition:

ANa_0.83^B(Na_0.83Mg_1.17)^CMg₅Si₈O₂₂(OH)₂.

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The IR spectra confirm the presence of both O-H and O-D bonds. Three absorption bands are present, for both H and D regions, similar to those reported in Iezzi et al., 2004. The two higher-frequency bands are due to the non-equivalent short O-H (O-D) bonds interacting with the ^ANa. In order to compare the structural behaviour between the room and low temperature forms and to gain new insights into the H(D)-O bonding, neutron powder diffraction data were collected at 293K and 4K on the SV7-diffractometer. Le Bail refinement of the cell parameters at room conditions shows lattice constant in good agreement with those obtained by single-crystal X-ray diffraction with a=9.7188(1),b=17.9385(2),c=5.2692 (1)Å, beta=102.527(1)° and a cell volume of 896.776(15)Å³. At 4K the amphibole structure still maintains a P-lattice structure, as confirmed by the presence of b-type reflections (h+k=2n+1) and the cell parameters become: a=9.7016(1), b=17.8954(3), c=5.2575(1)Å, beta=102.597(2)°, V= 890.805(15)Å³. The low-temperature effect on the crystal structure appears to be rather slight possibly due to saturation effects. Effectively no further LT-phase-transition was observed. Further Rietveld structural refinements will provide the exact H-positions, an overview of the low- temperature structural behavior and the main deformation mechanisms.

References:

Iezzi et al. (2004) Am. Mineral., in press Càmara et al. (2003) Phys.Chem.Min.,30, 570.

Fig.1: Na(NaMg)Mg5Si8O22(OH)2 amphibole structure viewed down a sinT (top) and down c (bottom).

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Experimental Report

of Neutron Scattering Experiments at the FRJ-2 Reactor

Experiment title: Proben mit schwacher Textur – Untersuchung von Effekten der Probenform bei experimentell bestimmten Polfiguren

Dates of experiment: 11 Tage in der Zeit vom 07.04.03 bis 29.07.03

Experimental team:

Names Addresses

H. Siemes Institut für Mineralogie und Lagerstättenlehre RWTH-Aachen

Bunsenstr. 8 52056 Aachen

Local Contact: E. Jansen, Univ. Bonn

Experimental report text body Motivation

Wegen ihrer hohen Durchdringungsfähigkeit eignen sich Neutronen in besonderer Weise zur Bestimmung von Volumentexturen, gerade auch an relativ großen Proben von z.B. mehreren cm³. Im Rahmen experimenteller Polfigurscans werden gerade im Fall geologischer Proben oftmals würfelförmige oder zylindrische Probenfor- men verwendet, um Probenflächen oder Probenachsen direkt mit den geologischen Feldbefunden wie z.B. geo- graphische Ausrichtung des Gesteins, Foliation oder Lineation markieren zu können. Bei der Bestimmung der Polfiguren aus den experimentellen Messdaten können in der Regel Absorptionskorrekturen vernachlässigt werden, obwohl dies idealerweise nur bei kugelförmigen Proben gilt.

Im Rahmen von Texturuntersuchungen an einer Vielzahl von Hämatit- bzw. Itabiriterzen (Hämatit + Quarz) aus Südafrika (SV7-02-007), Indien (SV7-02-014) und Brasilien (SV7-02-024), die im vergangenen Jahr am Tex- turdiffraktometer SV7-b erfolgten, zeigten einige Proben Poldichteverteilungen, die untereinander als kristallo- graphisch nicht konsistent anzusehen waren. Diese fraglichen Polfiguren zeichnen sich durch eine auffällig vierzählige Symmetrie in den Poldichten aus. Da diese untersuchten Proben alle würfelförmig geschnitten waren (Kantenlänge ca. 10 mm) kann die Probenform Ursache der vierzähligen Symmetrie in den gefundenen Poldichten sein.

Aufgabenstellung

Im Rahmen dieses neuen Projektes werden ausgesuchte Proben, die als Würfel vermessen wurden, durch Kanten- und Eckenabschliff nachgearbeitet, um so die gewünschte Kugelform besser anzunähern. Nach erneuter Messung der nachgearbeiteten Proben sollte die Ursache für die Vierzähligkeit ermitelbar sein.

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Form Version: 19.02.03 2 Vergleich würfelförmiger mit kugelförmigen Proben

Die folgenden Abbildungen zeigen jeweils 3 charakteristische Polfiguren aus den Messungen an drei Proben in Würfelform und den Messungen nach Abstumpfen der Kanten und Ecken der Würfel. In den Polfiguren sind in der linken untere Ecke die maximale und minimale Dichte (m.r.d. = multiples of random density 1.0), in der rechten unteren Ecke die 1. Isoliniendichte und die Dichtestufung angegeben.

Das Neutronendiffraktogramm der sehr schwach geregelten Probe der RJ3 (Abb. 1) weist lediglich Hämatit als Mineral aus. Derartige schwache Regelungen mit der Dichte 1.3 der (003)-Polfiguren werden in auffälliger Weise durch die Würfelform der Proben beeinflußt, denn nach der Rundung der Proben ist die Vierzähligkeit nicht mehr oder kaum noch zu erkennen. Diese Aussage gilt auch für die Probe SH2 und SH4.

Alle anderen würfelförmigen Proben, die eine Vierzähligkeit in den Polfiguren aufweisen enthalten neben Hämatit insbesondere Quarz, aber auch Magnetit und Goethit. Hämatit und Quarz bilden mehr oder weniger dünne, miteinander abwechselnde Lagen. In sehr stark geregelten Hämatitproben mit Gehalten anderer Mineral- komponenten war eine derartige Vierzähligkeit in den Polfiguren niemals festgestellt worden. Bei der Probe AL1, die mit einer max. Dichte 5.3 der (003)-Polfigur als deutlich geregelt angesprochen werden muß, liegt noch eine starke Vierzähligkeit vor, wie die Abb. 3, links zeigt. Nach der Rundung der Probe war die auffallen- de Vierzähligkeit verschwunden, wie es in der Abb. 3, rechts zu erkennen ist. Das Neutronenbeugungsdia- gramm zeigt neben dem vorherrschen Hämatit deutliche Anteile von Magnetit, Goethit und Quarz. Die Probe AL58, die ähnlich der Probe AL1 mit einer max. Dichte der (003)-Polfigur bei 5.2 ist, enthält keinen Goethit, so daß man einen Einfluß von Goethit ausschließen kann. Alle anderen Proben SH9, AL12, AL90, AL116 sind schwach geregelt mit max. Dichten der (003)-Polfiguren von 1.5 bis 2.6 und enthalten Quarz als Hauptkompo- nente neben dem Hämatit. Bei der schwach geregelten Probe AL116 (Abb. 2) konnte die Vierzähligkeit in den Polfiguren auch nach mehrmaliger Bearbeitung der Probe mit immer stärkerer Rundung nicht zum verschwin- den gebracht werden.

Halbwertsdicken d1/2 als Transmissionmaß für Neutronenstrahlung (1.0 A), Tabelle 2 in: H.-G. Brokmeier, Texturanalyse mittels winkeldispersiver neutronographischer Kernstreuung, GKSS-Bericht 95/E/9, 1995.

Hämatit: 9160 Pm Magnetit: 9290 Pm Goethit: xxxx Pm Quarz: 24300 Pm Kriterien für das Auftreten einer auf die würfelige Probenform zurückzuführende Vierzähligkeit sind schwache Regelungen und/oder eine Wechsellagerung von Hämatit mit mm-dicken Lagen von Quarz, dessen Transmission für Neutronenstrahlung mehr als doppelt so hoch ist wie für Hämatit, Magnetit und Goethit.

In allen gerundeten Proben konnnte man die Quarzlagen makroskopisch gut erkennen, während in den anderen Proben der Quarz makroskopisch nicht erkennbar war.

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Experimental Report

of Neutron Scattering Experiments at the FRJ-2 Reactor

Experiment title: Relations between microstructures and crystallographic preferred orientations in quartzites of the Western Alps

Dates of experiment: 5 days between 23/07/03 and 09/09/03

Experimental team:

Names Addresses S. Roller

N. Froitzheim

Geologisches Institut Universität Bonn Nussallee 8 D-53115 Bonn

Local Contact: E. Jansen, Universität Bonn Experimental report text body

Analysis of microstructures and crystallographic preferred orientations (CPO) of quartz domains can resolve questions about single- and polyphase deformation along ductile shear zones. The simple shear deformation acting on quartzites induces systematic modification of the crystal lattices and results in a preferred orientiation of crystallographic axes.

One of the prominent zones of movement in the Western Alps, the Combin fault zone, both possesses an unresolved kinematic history and a thin layer of mylonitic quartzites at its base. Along the Combin fault zone, high-grade metamorphic ophiolitic rocks of the Zermatt zone are juxtaposed to structurally higher low-grade metasedimentary rocks of the Cimes Blanches nappe and ophiolites of the Tsaté nappe. The hiatus between eclogite and greenschist facies metamorphism suggests a considerable amount of offset along this zone. During the first campaign samples were taken in the Valtournenche (Italy) north of Lago de Cignana from the lower parts of the Combin fault zone.

So far, comparison of lattice and grain shape orientations observed under the optical microscope and of CPO patterns of a few samples (GP 38, GP 40, GP 41) largely show agreement in terms of movement direction.

GP 38 shows distinct top-SE shear in thin section and sinistral shear in the CPO pattern for c-axes which also corresponds to top SE-shear. The CPO pattern of GP 40 also displays top-SE shear. For GP 41 the thin section shows a more complicated structure with dynamically recrystallized quartz domains, rotated feldspar porphyroclasts and with mica fish mainly with top-NW shear sense but locally overprinted by top-SE microstructures. This situation can also be found in the CPO pattern of GP 41: assuming simple-shear deformation, the sample was first sheared sinistrally (i.e. top-NW), later dextrally (i.e. top-SE), while the older pattern was not completely overprinted.

The basic conclusion of these first results is that during polyphase deformation the Combin zone first acted as NW-directed thrust zone and later was inverted to a SE-directed normal fault zone. This has severe influence on

Neutron Scattering at FRJ-2