K. Bormanis

Effect of Zr4+ Doping on the Electrical Properties of BaTiO3 Ceramics

The BaZrxTi1-xO3 for 0⩽x⩽15 ceramics were prepared by a conventional solid state reaction method and were determined by an X-ray diffraction (XRD) and scanning electron microscopy (SEM) for crystallographic, surface morphological and compositional studies. A single phase with perovskite structure was identified in the samples at room temperature. No significant impurities were detected in an EDS spectrum and the samples are in good stoichiometric ratio. The temperature dependence of electric conductivity was evaluated in the temperature range from 300 to 550 K for a selected frequency by a HP4284 LCR meter. The activation energy was calculated from the Arrhenius plots.

The Electrical Properties of Ba1-ySryZrxTi1-xO3 Solid Solution

A lead-free solid solution Ba0.80Sr0.20Ti0.75Zr0.25O3 was prepared by a conventional technology. The structure and morphology of investgated samples were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The studies of electric conductivity were performed depending on temperature and frequency of electric measuring field. The activation energy was calculated from the Arrhenius plots.

Thermophysical properties of PLZT ferroelectric ceramics with a nanopolar structure

The heat capacity, thermal expansion coefficient, and deformation of the PLZT-9/65/35 compound are studied in the temperature range 150–800 K. Diffuse anomalies are detected in the temperature dependences of the heat capacity and thermal expansion coefficient over wide temperature ranges of 250–650 and 330–550 K, respectively. The anomalous behavior of the heat capacity in the temperature range 250–650 K is shown to be caused by the appearance of two-level states (Schottky anomaly). The results obtained are discussed along with the data of structural and dielectric studies.

Dynamics of Polar Clusters in PMN Ceramics: Comparison with PMN Single Crystal

The dielectric permittivity of PMN ceramics was measured in the frequency range from 20 Hz to 37 GHz. From the frequency dependence of the real and imaginary parts of dielectric permittivity, the distribution of relaxation times f(τ) was calculated. The f(τ) function broadens significantly, and the second maximum appears below the 270 K temperature. The dielectric response and also relaxation time distribution of PMN ceramics was compared with the previous results of PMN single crystal. The results showed that dynamics of polar nano regions in PMN ceramics is suppressed due to the small size of grains in the ceramics.

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT Lead-free piezoelectric ceramics (K0.5Na0.5)(Nb1-xSbx)O3+0.5 mol.%MnO2, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO2 functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm3 for undoped (K0.5Na0.5)NbO3 to 4.40 g/cm3 for Mn/Sb5+ co-doped ceramics. The co-effects of MnO2 doping and Sb5+ substitution lead to significant improvement in dielectric and piezoelectric properties: ϵ at the Tc increased from 6000 (KNN) to 12400 (x = 0.04), d33 = 92 ÷ 192 pC/N, kp = 0.32 ÷ 0.46, kt = 0.34 ÷ 0.48.

Low temperature measurements by infrared spectroscopy in CoFe2O4 ceramic

This paper presents results of new far-infrared and middle-infrared measurements (wavenumber range of 4000–100 cm−1) of the CoFe2O4 ceramic in the temperature range from 300 K to 8 K. The band positions and their shapes remain constant across the wide temperature range. The quality of the sample was investigated by X-ray, EDS and EPMA studies. The CoFe2O4 retains the cubic structure (Fd - 3m) across the temperature range from 85 K to 360 K without any traces of distortion. Based on current knowledge the polycrystalline CoFe2O4 does not exhibit any phase transitions across the temperature range from 8 K to 300 K.

Phase transitions in ferroelectric solid solutions of Li0.12Na0.88TayNb1-yO3 (LNTN)

Abstract Ferroelectric solid solution (SS) samples of the Li x Na1-x TayNb1-y O3 (LNTN) system were synthesized to have x = 0.12 and y = 0 - 1, the density exceeding 96% of the theoretical value determined by X-ray diffraction. The effects of isovalent substitution in the B sublattice of LNTN SS of the ABO3 structure on phase transition temperature has been examined in a wide temperature range (-190 - + 800°C). Concentrational structure transitions have been observed in the LNTN system at substitution of Nb by Ta in the B sublattice.

FORMATION OF FRACTAL MICRO- AND NANO-STRUCTURES IN CERAMIC TANTALUM PENTOXIDE UNDER CONCENTRATED FLUX OF LIGHT AND THEIR EFFECT ON THERMAL EXPANSION

ABSTRACT Oxides of weak thermal expansion are the basis for stable ceramics and artefacts resistant to sharp cyclic variations of temperature. For technical applications is a wide interest in high-temperature materials of low or negative thermal expansion and, particularly, in studies of the micromechanisms in Ta2O5. Thermal expansion of ceramic pentoxides of tantalum is affected by conditions under which they are formed. After treatment by concentrated light flows anomalous segments of zero and even negative thermal expansion appear in ceramics of Ta2O5. The effect of treatment by concentrated light flux on formation of fractal nano-structures and thermal expansion of ceramic tantalum pentoxide was studied.

Kinetics of Photorefractive Light Scattering in LiNbO3:Cu and LiNbO3:Zn Single Crystals

Results of studies of the kinetics of photorefractive light scattering (PRLS) in optically nonlinear congruent single crystals of lithium niobate (LiNbO3, Li/Nb = 0.946) containing multivalent cation admixtures of Cu [0.015 mass %] (“photorefractive”) and Zn [0.5 mass %] (“non-photorefractive”) are reported. The shape of the PRLS indicatrix is found to be different in case of Cu and Zn admixtures. However, the angular widening of the indicatrix in both cases reaches its stationary value faster at higher laser radiation intensities. The PRLS is found to depend on the site of the ingot from which the samples are cut – an evidence of non-uniform distribution of defects with localised electrons determining the photorefractive effect in the bulk of the single crystal ingot.

Kinetics of Photorefractive Light Scattering in Stoichiometric LiNbO3 Single Crystals Grown from Melt Containing 58.6 Mole% of Li2O

A study of kinetics of photo-refractive light scattering in ostensibly pure stoichiometric LiNbO3 (Li/Nb = 1) single crystal grown from melt containing 58.6 mole% Li2O excited by laser radiation of 0.53 μm is reported. Asymmetry of the distribution of scattered light intensity is revealed and found to be a linear function of the intensity of the exciting radiation in the 35–160 mW range. Due to heating of the crystal, at farther increase of the radiation intensity the distribution of scattered light contracts.