Chapter 2 Experimental procedure
2.1 Characterizing Methods
2.1.1 Powder characterization
2.1.1.1 Particle size measurement
Particle size has a significant effect on the consolidation and sintering of the powder. In order to compare different samples, similar particle size is required. The particle size distribution of the powders was analyzed using laser light scattering (Malvern Mastersizer S, Herrenberg, Germany).
The device uses light scattering to measure the equivalent spherical diameter of particles. The powder was firstly dispersed in Isopropanol under ultrasonic treatment for 2 mins to break down soft agglomerates. The results showed a Gaussian distribution. D50 stands for the volume median diameter. D50 values were calculated and used to characterize the powders.
2.1.1.2 Optical Emission Spectrometry with Inductively Coupled Plasma
Since the impurity elements had a very low concentration, a technique with high precision and low detection limit is desirable. In the present work, the compositions of the raw materials were analyzed by Optical Emission Spectrometry with Inductively Coupled Plasma (ICP‐OES) using a Varian spectrometer (Varian Vista PRO, Springvale, Australia).
2.1.1.3 X‐ray diffraction and Rietveld refinement
X‐ray diffractometry (XRD) was employed to determine the phases present in the raw materials, and in calcined and sintered samples. The XRD experiments were performed in a Philips PW1710 X‐ray diffractometer with a step scan of 0.02° and a count time of 1s. Profiles were collected using filtered Cu Kα radiation with a wavelength of 1.5406 Å. Qualitative phase analysis was accomplished by comparison with JCPDS database (published by ICDD in 2004) for a matching pattern. Some of the XRD data were processed with the software “Topas” (Bruker AXS, Karlsruhe) based on Rietveld method that will be introduced in the Chapter 3.
2.1.1.4 DTA TG
Simultaneous differential thermal analysis (DTA) and thermo‐gravimetric analysis (TG) were carried out by a Netzsch STA 449C equipment. The measurement was performed in air with a heat
20 2.1 Characterizing Methods
rate of 10K/min to 850°C. The weight of each sample was approximately 0.2g, within small variations.
2.1.2 Characterization of sintered PZT ceramics
2.1.2.1 SEM, EDS and Grain size measurement
Scanning electron microscopy (Supra 25, Zeiss, Oberkochen, Germany) was used to observe the microstructure in combination with energy dispersive X‐ray spectrometry (EDS) to determine the local composition. To examine the polished surfaces of green samples or porous samples, they were specially prepared to prevent damaging of microstructure from polishing. They were first fixed by a holder and placed in a plastic bottle. After the bottle was evacuated for 15 mins, a mixture of EpoHeat resin and EpoHeat hardener (Buehler GmbH, Düsseldorf, Germany) were poured into it and infiltrated into pores in the samples. After curing at 60°C for 2 hours, the resin cylinders with samples inside were polished with sand paper of 600 grades till the surface of the samples appeared. The section was subsequently polished with sand paper 1200, 2500, 3μm diamond suspension and 1μm diamond suspension. Then, the resin body was softened at 200°C on a hot plate and the polished samples were taken out and thermally‐etched at 800°C for 1 hour.
2.1.2.2 TEM and FIB
Transmission electron microscopy (TEM, JEM‐2010, JEOL) was employed to analyze the thin film on the grain boundaries of quenched samples as well as the crystalline nature of these phases. EDS experiments were carried out with the EDAX instrument attached on the TEM column analysed with Genesis Spectrum software (EDAX Inc., Mahwah, NJ 07430, USA). The sample was prepared by the Focused Ion Beam (FIB) technique (Quanta 200 3D, FEI Company, Eindhoven, The Netherlands). The instrument uses gallium ion source. The 30 kV Ga+ ions and beam current of 10 pA‐7nA were used to prepare the specimen. The working process was observed through an electron microscope.
2.1.2.3 XPS measurements
X‐ray Photoelectron Spectroscopy (XPS) were performed on the fracture surfaces of sintered samples. Monochromatic Al Kα x‐rays are used for the excitation of the sample. After the direct measurement, the fractured surfaces were sputtered for different time and measured once more to gain the information from near surface or bulk regions as well. Sputtering was done by a VG EX05 scanning ion gun with Ar+ ions. The erosion rate measured on SiO2/TiO2 multilayer material was 10nm per 100s sputtering time. In present study, a sputtering time of 20 s and 4020s were used.
Chapter 2 Experimental procedure 21
2.1.2.4 Density measurement
The density of samples was measured by Archimedes’s method with distilled water as liquid medium. The temperature of each measurement was recorded, to use the respective density of water. For each composition, three runs on three different samples were carried out. The average and standard error were calculated.
2.1.2.5 Dielectric properties and piezoelectric properties
Silver paste with a diameter of 7.5 mm was printed on both sides of the discs and fired at 600°C to form the electrodes. For dielectric and piezoelectric characterization, the specimens with electrodes were polarized in silicon oil at 120°C for 5 min by applying an electric field of 2.1kV/mm. The dielectric constants and electromechanical coupling factors were measured by the series resonance and parallel resonance method using a precision impedance analyzer Agilent 4294. The piezoelectric coefficient d33 was determined by a Berlincourt measurement device. All dielectric and piezoelectric quantities reported are averages over at least 3 samples.
fp: parallel resonance frequency; fs: series resonance frequency; C: capacitance; Zs: impedance at resonance; A: electrode area; tD: thickness of the discs; ε0: the permittivity of free space, 8.85×10‐12 F/m
2.1.2.6 Ferroelectric properties
The P‐E (polarization vs. field) measurements were made by using a computer controlled Sawyer‐
Tower circuit with a four channel oscilloscope TDS460 (Tektronix Inc., USA). Investigations of the P‐E hysteresis loop were performed as a function of AC drive excitation under a frequency of 5 Hz (Frequency generator PM5138A, Fluke Corporation, USA) at room temperature. The AC electric fields ranging from 5kV/cm to 30kV/cm were achieved by a high voltage amplifier (P0610, Trek Inc., USA). The measurement was performed in air at room temperature.