No abstract

Complex impedance spectra of BST ceramics were measured at different temperatures, and the results reveal that all the centers of the semicircles lie below the real axis, and the area of the semicircles decreases with the increasing temperature. Activation energy of grains and grain boundaries was obtained from a classical Arrhenius relation. The results show that the activation energy of grains and grain boundaries of undoped BST ceramics is 0.98 and 0.97 eV, respectively. After doping B 2 O 3 -SiO 2 , the activation energy of grain increased to 1.12 eV, which was due to B 2 O 3 -SiO 2 redistribution to the grain boundary during the cooling process. The activation energy of grains increased to 1.16 eV after 1 mol% MgO doping, which was caused by the decrease of the oxygen vacancy concentration and the increase of the potential barrier of the grain boundary.

Abstract

No abstract

Ba 0.65 Sr 0.35 TiO 3 (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at l=650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of asdeposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.