Cubic and Tetragonal Modifications in BaTiO 3 Ceramic Samples: X-Ray Diffraction Analysis by the Rietveld Method
- PDF / 793,316 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 206 Views
MICS
Cubic and Tetragonal Modifications in BaTiO3 Ceramic Samples: X-Ray Diffraction Analysis by the Rietveld Method A. A. Busha, V. P. Sirotinkinb,*, and S. A. Ivanovc a Russian
b
Technological University (MIREA), Moscow, 119454 Russia Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Moscow, 119334 Russia c Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received December 9, 2019; revised April 19, 2020; accepted April 20, 2020
Abstract—The structures of ground ceramic BaTiO3 samples, prepared by solid-phase synthesis at maximum sintering temperatures of 1350, 1400, 1410, and 1500°C, have been analyzed by the Rietveld method. It is shown that, along with the tetragonal phase, the samples contain the cubic BaTiO3 phase with an effective content of about 30 vol %. The cubic phase was observed as a thin layer on the surface of ceramics grains with tetragonal structure. The efficiency of preliminary analysis of specific ranges of X-ray diffraction patterns containing strong peaks is demonstrated. DOI: 10.1134/S106377452005003X
INTRODUCTION Barium titanate (BaTiO3) belongs to ferroelectrics that are thoroughly studied and widely used in electronic devices [1–4]. It undergoes phase transitions at 1432, 130, 5, and –90°C, at which the crystal-structure symmetry changes successively from hexagonal to cubic, tetragonal, orthorhombic, and rhombohedral, respectively. At room temperature, the tetragonal ferroelectric BaTiO3 phase with a perovskite-type structure and the Curie point at 130°C is stable. High permittivity ε; low dissipation factor tanδ; and specific features of electric, piezoelectric, pyroelectric, and other properties make BaTiO3 and a variety of solid solutions on its basis promising capacitive materials (in particular, media for multilayer ceramic capacitors, variable resistors, resistors with positive temperature coefficient, ultrasonic converters, piezoelectric devices, pyroelectric detectors, energy storage devices, etc.). The dielectric and other properties of BaTiO3 powders and ceramics depend strongly on the method and conditions of their synthesis [5–24]. This influence is due to several factors: an increase in the ceramics density and, therefore, reduction of its porosity with an increase in the sintering temperature; dependence of the ceramics grain size on the sintering temperature and time (which, in turn, affects the sizes of ferroelectric domains in grains and the fraction of low-permittivity intergranular interlayers in the ceramics); and
the BaO volatility at high temperatures, which leads to a change in the [Ba]/[Ti] stoichiometry in barium titanate samples. The dielectric and other properties of powder and ceramic BaTiO3 samples are determined in many respects by the grain size (a grain has a composite structure and consists of a core and a shell) [7–9, 12, 13, 15–17, 19]. At room temperature, the core has a tetragonal symmetry and exhibit ferroelectric properties [7–9, 19, 25–30], whereas the shell structure is not te
Data Loading...
