A New Layered Chalcogenide in the System NiIn2

A New Layered Chalcogenide in the System NiIn₂S₄-NiIn₂Se₄ A. Memo and H. Haeuseler

Laboratorium f ¨ur Anorganische Chemie, Universit¨at Siegen, D-57068 Siegen Reprint requests to Prof. Dr. H. Haeuseler. E-mail: haeuseler@chemie.uni-siegen.de Z. Naturforsch.57 b,509–511 (2002); received January 7, 2002

Layered Materials, Phase Diagram, Chalcogenide

The system (1 –x)NiIn2S4 -xNiIn2Se4 has been investigated by X-ray powder methods.

The subsolidus phase diagram is constructed in the temperature interval 600 -1000^þC. The spinel type NiIn2S4 exhibits a phase width up to the composition NiIn2S2Se2at 900^þC and NiIn2S2^:8Se1^:2at 600^þC. A new layered compound is formed for 0.7^ÿx^ÿ0.5 at 600^þC and forx= 0.6 at 900^þC which crystallizes in the MgAl2S4-type witha= 392.4 andc= 3739.6 pm (x= 0.6) for the hexagonal cell.

Introduction

In recent years, we reported on a series of sub- solidus phase diagrams of chalcogenide systems with a mixed sulfide / selenide anion substructure in which we found new compounds crystallizing in the centrosymmetric MgAl₂S₄-structure: CdIn₂S₄- CdIn2Se4[1], MnIn2S4-MnIn2Se4[2] and FeIn2S4- FeIn₂Se₄ [3]. The formation of this structure and its polytypes in these systems is ascribed to the enhancement of the preference for tetrahedral co- ordination with increasing amount of selenium in the samples [4]. Starting from the spinel type com- pounds (CdIn₂S₄, MnIn₂S₄and FeIn₂S₄) where the ratio of the number of octahedrally coordinated noto the number of tetrahedrally coordinated n_t cations is n_o : n_t = 2 : 1, growing tetrahedral site prefer- ence can lead to a structure where this ratio is 1 : 2 which is found in the layered structure of MgAl₂S₄ and its polytypes. We therefore expected that in the case of the spinel NiIn₂S₄ [5] a mixed sulfur-se- lenium compound with a layered structure might also exist and started an investigation of the system NiIn₂S₄-NiIn₂Se₄. To the best of our knowledge a compound of composition NiIn2Se4does not exist, we therefore write this composition in parenthesis.

Experimental Section

Samples of NiIn2SxSe4^þxwith 0^þx^þ4 were pre- pared by sintering stoichiometric mixtures of the binary sulfides in evacuated, sealed silica ampoules at 800 ^ÿC.

After a reaction time of 6 days the samples were homog- enized, divided in 4 equal parts and these fired again two

0932–0776/02/0500–0509 $ 06.00 c^ÿ2002 Verlag der Zeitschrift f¨ur Naturforschung, T¨ubingen^þwww.znaturforsch.com K

times each for 10, 8, 6 and 4 days at 600, 700, 800, and 900^ÿC, respectively. After the second heat treatment the compounds were quenched to room temperature.

The samples obtained after the different heat treat- ments were analysed by X-ray investigations with Cu- K^ÿ₁(^ÿ= 154.05 pm) radiation. The cell parameters were computed from diffraction data obtained from a Siemens powder diffractometer D5000 with transmission-primary monochromator and a Braun GmbH PSD-50M scanning position sensitive detection system. Indexing and refine- ment of the powder patterns were made with the program package VISUAL X^POW[6].

Results and Discussion

As can be seen from the experimental data, the system NiIn₂S₄- “NiIn₂Se₄” is not quasibinary in the investigated temperature range due to the fact that the ternary selenide NiIn₂Se₄ does not ex- ist. The X-ray powder diffraction patterns of the quaternary compositions in the system NiIn2S4 -

“NiIn₂Se₄” show the existence of four different phases. In addition to the end-member compound NiIn₂S₄ [5] there is a second phase with a pow- der pattern characteristic of compounds crystalliz- ing in the acentric ZnIn₂S₄(IIIa)-type [7] or in the centrosymmetric MgAl₂S₄-type [8] at high temper- atures. By analogy with the results of Rangeet al.[9]

we assume that the high temperature phase adopts the centrosymmetric MgAl2S4-structure. NiIn2Se4

does not exist, and the samples in the selenium-rich region of the phase diagram therefore are composed of two or more different phases. The phase diagram constructed from these results is shown in Fig. 1.

510 A. Memo and H. Haeuseler · A New Layered Chalcogenide in the System NiIn₂S₄-NiIn₂Se₄ Table 1. Lattice parameters of the samples crystallizing

with the hexagonal layer structure of MgAl2S4type and the cubic spinel type in the system xNiIn2S4 - (1 –x)

“NiIn2Se4” quenched at 700^þC.

Sample Layer structure Spinel-type a( ˚A) c( ˚A) a( ˚A) NiIn2S1^:2Se2^:8 3.940 37.674

NiIn2S1^:6Se2^:4 3.924 37.396 NiIn2S2Se2 3.912 37.282

NiIn2S2^:4Se1^:6 3.894 37.066 10.992

NiIn2S2^:8Se1^:2 10.804

NiIn2S2^:2Se0^:8 10.684

NiIn2S3^:6Se0^:4 10.610

NiIn2S4 10.513

Fig. 1. Subsolidus phase diagram of the systemxNiIn2S4

- (1 –x)“NiIn2Se4”.

The lattice parameters obtained for the different phases in the samples of different composition are tabulated in Table 1. These data show that single phase samples with spinel structure can be obtained for 1^ÿ x^ÿ 0.7 at 600^ÿC and for 1^ÿx^ÿ0.5 at 900^ÿC, with the border compositions NiIn₂S₂:8Se₁:2

at 600^ÿC and NiIn₂S₂Se₂at 900^ÿC. Samples with the layered structure of MgAl2S4-type are formed for 0.5^ÿx^ÿ0.3 at 600^ÿC and forx= 0.4 only at 900^ÿC. For the compound withx= 0.5 the powder diffraction data are compiled in Table 2. The phase widths of both the spinel and the layered structure show a markable dependence on temperature with the phase widths of the spinel growing with temper- ature and the phase width of the layered structure decreasing. From the narrowing of the phase width of the layered structure one can suppose that at tem- peratures above 900 ^ÿC the sample with x = 0.4 decomposes or undergoes a phase transition to the spinel type. Experiments to prove this supposition

Table 2. Powder diffraction data of NiIn2S2Se2(MgAl2S4

type) quenched at 700^þC.

h k l d_obs d_calc Int. h k l d_obs d_calc Int.

0 0 8 4.6588 4.6602 27.9 2 0 4 1.6668 1.6666 8.2 0 0 9 4.1483 4.1424 12.5 2 0 28 1.5911 1.5920 18.1 0 0 1 3.3885 3.3892 66.8 0 0 24 1.5548 1.5534 3.2 1 0 0 3.3878 2 0 22 1.4872 1.4872 3.0 1 0 4 3.1844 3.1840 44.4 1 0 24 1.4116 1.4120 3.7 1 0 8 3.7403 2.7403 85.6 2 0 16 1.3702 1.3701 7.9 0 0 5 2.4863 2.4854 5.3 1 1 20 1.3493 1.3494 5.1 1 0 1 2.3915 2.3961 4.8 2 0 19 1.2808 1.2822 4.5 1 0 2 2.2895 2.2898 13.4 1 1 22 1.2808 0 0 8 2.0713 2.0712 5.0 2 1 0 1.2805 1 1 0 1.9564 1.9560 100.0 2 1 1 1.2797 1 1 1 1.9533 2 1 4 1.2699 1.2686 4.8 1 0 6 1.9195 1.9198 30.3 2 1 8 1.2346 1.2347 10.4 1 1 6 1.8625 1.8657 6.1 1 1 24 1.2169 1.2164 4.5 0 0 0 1.8641 2 1 12 1.1835 1.1839 2.9 1 1 8 1.8037 1.8036 12.6 2 0 24 1.1443 1.1449 2.9 1 0 19 1.6952 1.6980 8.2 0 0 33 1.1299 1.1297 8.2

0 0 2 1.6946 3 0 0 1.1293

1 1 1 1.6941 2 1 16 1.1221 1.1222 7.4

2 0 0 1.6939 3 0 4 1.1211

failed as the sample melts. As would be expected from Vegard’s law, the lattice parameters of the lay- ered mixed crystals as well as of those with a spinel structure show a linear dependence on the compo- sition.

Experiments to grow single crystals of the layer type compounds by recrystallization with a small amount of iodine did not result in crystals of good quality which could be used for single crys- tal measurements. A comparison with the corre- sponding systems CdIn2S4-CdIn2Se4[1], MnIn2S4- MnIn₂Se₄[2], and FeIn₂S₄-FeIn₂Se₄[3] shows that at 800 ^ÿC in all these systems in the phase with spinel structure 20 - 30 % of the sulfur may be replaced by selenium atoms. The phase width of the compound crystallizing in the layered, centro- symmetric MgAl₂S₄-structure on the other hand changes significantly from system to system. Espe- cially large is the homogeneity range of MnIn₂S₂Se₂ which is not at all surprising as for the pure selenide MnIn2Se4 Range et al. [10] reported on a poly- morph with the MgAl₂S₄ type structure. FeIn₂Se₄ also crystallizes in a layered yet unknown structure [3, 11], for which we suppose that (i) it is similar to one of those in the system Zn-In-S and (ii) exhibits a large homogeneity range. Thus in the cases of Mn and Fe phases with layered structures are formed for 0.6^ÿx^ÿ0.

A. Memo and H. Haeuseler · A New Layered Chalcogenide in the System NiIn₂S₄-NiIn₂Se₄ 511 Acknowledgement

Support of this research by the Deutsche Forschungs- gemeinschaft is gratefully appreciated.

[1] H. Haeuseler, J. Solid State Chem.29, 121 (1979).

[2] H. Haeuseler, W. Cordes, D. Reinen, U. Kesper, J. Solid State Chem.106, 501 (1993).

[3] S. Reil, H. Haeuseler, J. Alloys Comp. 270, 83 (1998).

[4] H. D. Lutz, W. Buchmeier, H. Siwert, Z. Anorg. Allg.

Chem.533, 118 (1986).

[5] H. D. Lutz, M. Jung, Z. Anorg. Allg. Chem.579, 57 (1989).

[6] VISUAL X^POW, Version 2.2, Stoe Powder Diffrac- tion Software, Stoe&CIE GmbH, Darmstadt (1994).

[7] F. Lappe, A. Niggli, R. Nitsche, J. G. White, Z. Kri- stallogr.117, 146 (1962).

[8] J. Flahaut, Ann. Chim.7, 632 (1952).

[9] N. Berand, K.-J. Range, J. Alloys Comp.205, 295 (1994).

[10] K.-J. Range, U. Klement, G. D ¨oll, E. Bucher, J. R.

Baumann, Z. Naturforsch.46b, 1122 (1991).

[11] P. G. Rustamov, B. K. Babaeva, R. S. Gamdor, M. A. Alizhamov, Azerb. Khim. Zh. 1976, 120 (1990).