Papers by Keyword: Tolerance Factor

Abstract: Ca1–3xLn2xTiO3 (Ln=La, Nd, Sm; x=0.13, 0.20) ceramics were investigated systematically to dicuss the influences of sintering temperature, compositions, Ln3+ ions on its sintering property, crystal structure and microstructure. The results show that the dense ceramics were obtained in the sintering temperature range of 1300~1350 °C and the relative density reached over 97%. Sintering temperature was 50~150 °C lower than previous reports. Single orthogonal perovskite structure phase was formed except that a little secondary phase Sm2Ti2O7 was detected by XRD analysis when x=0.20 and Ln=Sm. The growth pattern of Ca1–3xLn2xTiO3 grains was terracing growth.

Abstract: The structural, and dielectric and piezoelectric properties of (1-x)BaTiO3 – x Bi_1/2K_1/2(X_1/3Nb_2/3)O₃ (X=Cu, X=Mg or X=Zn) ceramic were studied. The single perovskite phase was observed when x≤0.5 for X=Cu and Mg and x≤0.2 for X=Zn. As x increased, the dielectric constant peak temperature and piezoelectric properties continuously decreased for X=Mg and Zn. On the other hand, those of X=Cu possessed a local maxima at x=0.7 and the peak temperature was 200°C and the large field piezoelectric constant, d₃₃*, was 94 pC/N.

Abstract: In complex perovskite-type oxides which have been studied as cathode materials, the thermal expansion coefficient increases with the increase in the oxygen ionic conductivity. In the present study, with the aim to explain such a behavior, a research has been carried out from a chemical bond point of view. For oxides A1-xA′xB1-yB′yO with perovskite structure, the ionicity of the individual bond, A-O and B-O, and the thermal expansion coefficient of mixed compounds were estimated by using semiempirical methods. It has been shown that the thermal expansion coefficient and the oxygen ionic conductivity decrease with the increase in the difference of the ionicity between A-O and B-O bonds. It is also found that the tolerance factor and the specific free volume are linearly correlated with the difference of ionicity.

Abstract: The relationship between the character of the B-site cation–oxygen bond and the microwave dielectric properties in perovskites dielectric materials was studied in this paper. The atomic net charge of CaTiO3 (CT) and Ca(Zn1/3Nb2/3)O3 (CZN) was calculated respectively. The calculating result implies that the covalency of B-O bonds in CZN is stronger than that in CT. This predicted that the dielectric constant and loss of the ceramics will decrease after CZN incorporated in CT. To confirme the prediction, (1-x)CT-xCZN microwave dielectric ceramics were prepared by solid state reaction method with ZnNb2O6 as precursor. The structure analysis in terms of tolerance factor gives an identical result as calculation. The microwave dielectric properties, such as dielectric constants, Q×f values and τf were studied as a function of composition. With x increasing from 0.2 to 0.8, the dielectric constant linearly decreases from 109 to 49.37, the Q×f value increases from 8,340 to 13,200 GHz, and τf decreases from 321 to -18 ppm/°C. The properties trends are consistent with the previous calculation results, and confirm the relationship between the character of B-O bond and dielectric properties.