X.M. Chen

Crystal structure and dielectric properties of ferroelectric ceramics in the BaO-Sm2O3-TiO2-Nb2O5 system

Abstract Some tungsten–bronze ferroelectrics were synthesized and characterized in the BaO-Sm2O3-TiO2-Nb2O5 system. Ba4Sm2Ti4Nb6O30 and Ba5SmTi3Nb7O30 had the tetragonal filled tungsten–bronze structure; while Ba3Sm3Ti5Nb5O30 consisted of the orthorhombic tungsten–bronze major phase and the BaTi4O9 secondary phase. The present dielectric ceramics exhibited relaxor behavior with the maximum temperatures around 185, 285 and 130xa0°C for Ba3Sm3Ti5Nb5O30, Ba4Sm2Ti4Nb6O30 and Ba5SmTi3Nb7O30, respectively. Moreover, Ba3Sm3Ti5Nb5O30 exhibited a second possible phase transition around 93xa0°C.

Raman spectra analysis for Ca(B1/3′B2/3″)O3-based complex perovskite ceramics

Ca[(Mg1/3Ta2/3)1−xTix]O3 (hereafter denoted as CMTT) and (Ca1−0.39xNd0.26x) [(Mg1/3Nb2/3)1−xTix]O3 (hereafter denoted as CNMNT) complex perovskite ceramics were studied by Raman spectroscopy combined with Rietveld analysis. The crystal structures changed from monoclinic structure with P21/c space group to orthorhombic structure with Pbnm space group for both systems. The main structure of the two systems was orthorhombic and the characteristic modes for the orthorhombic structure with space group Pbnm could be found in all the compositions. Raman modes at around 408u2002cm−1 could only be found for compositions with 1:2 long range cation ordering while modes at around 800u2002cm−1 could be found for all the compositions in both systems. They were concluded to be correlated with the 1:2 long range cation ordering and different short range cation ordering, respectively. Two Ag modes at around 800u2002cm−1 represented for 1:2 and 1:1 short range cation ordering were observed for CMTT ceramics with x=0.1–0.6 while only 1...

A novel route to lower the dielectric loss in CaCu

Based upon a widely-accepted internal-barrier-layer-capacitance (IBLC) model, the dielectric loss in the giant-dielectric-constant CaCu

_{3}

_{3}

Ti

Ti

_{4}

_{4}

O

O

_{12}

_{12}

ceramics

(CCTO) material is expected to decrease as the conductivity of the CCTO grains/subgrains increases. In this letter, we report that this idea was successfully realized through the La-for-Ca substitution in the CCTO ceramics. The impedance spectroscopy analysis gives the evidence.