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/ 709 699 43 M20 M21 The crystal structure and microstructure of as-prepared and annealed Ni0.9Zn0.1O were refined at room temperature in both the Fm (3) over barm and R (3) over barm space groups. It is shown that below the Neel point (458 K), where magnetic ordering triggers the presence of a trigonal strain, the common usage of a higher-symmetry non-admissible space group for crystal structure and microstructure analysis via the Rietveld method may result in both an incorrect structure description and incorrect microstructure parameters (size and strain). More realistic microstructure data can be obtained by whole powder pattern modelling of the powder diffraction data. Increasing the annealing temperature causes a reduction of the trigonal distortion as well as an increase in domain size. Simultaneously, the Raman spectra become less resolved, a clear indication of domain growth and structural evolution of the structure towards cubic symmetry (R (3) over barm - GT Fm (3) over barm).

Powder mixtures of alpha-Bi2O3 (bismite) and monoclinic m-ZrO2 (baddeleyite) in the molar ratio 2:3 were mechanochemically and thermally treated with the goal to examine the phases, which may appear during such procedures. The prepared samples were characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), electrical measurements, as well as scanning electron microscopy (SEM) and transmission election microscopy (TEM). The mechanochemical reaction leads to the gradual formation of a nanocrystalline phase, which resembles delta-Bi2O3, a high-temperature Bi2O3 polymorph. Isothermal sintering in air at a temperature of 820 degrees C for 24 h followed by quenching to room temperature yielded a mixture of ZrO2-stabilized beta-Bi2O3 and m-ZrO2 phases, whereas in slowly cooled products, the complete separation of the initial alpha-Bi2O3 and m-ZrO2 constituents was observed. The dielectric permittivity of the sintered samples significantly depended on the temperature. The sintered and quenched samples exhibited a hysteresis dependence of the dielectric shift, showing that the ZrO2-doped beta-Bi2O3 phase possess ferroelectric properties, which were detected for the first time. This fact, together with Rietveld refinement of the beta-Bi2O3/m-ZrO2 mixture based on neutron powder diffraction data showed that ZrO2-doped beta-Bi2O3 has a non-centrosymmetric structure with P $(4) over bar $2(1)c as the true space group. The ZrO2 content in the doped beta-Bi2O3 and the crystal chemical reasons for the stabilization of the beta-Bi2O3 phase by the addition Of m-ZrO2 are discussed. (c) 2008 Elsevier Inc. All rights reserved.

Multilayered BaTi1-xSnxO3 (BTS) ceramics with different Ti/Sn ratios were produced by pressing and sintering at 1420 degrees C for 2 hours. X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy were used for structural, microstructural and elemental analysis, respectively. The dielectric and ferroelectric behavior of sintered samples was studied, too. It is found that in ingredient materials, with increasing Sri content, the tetragonality decreases; Curie temperature moves towards room temperature, while the maximum of the dielectric constant increases, and also, they becomes less hysteretic. It is noticed that multilayered BTS ceramics with different Ti/Sn contents have a broad transition temperature and show a relatively high dielectric constant in a wide temperature range. It is shown that dielectric properties of these materials may be modified by a combination of different BTS powders as well as layers number. Research Trends in Contemporary Materials Science, 8th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 04-08, 2006, Herceg Novi, Montenegro