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

Ca[(Mg1/3Ta2/3)(1-x)Ti-x]O-3 (hereafter denoted as CMTT) and (Ca1-0.39xNd0.26x) [(Mg1/3Nb2/3)(1-x)Ti-x]O-3 (hereafter denoted as CNMNT) complex perovskite ceramics were studied by Raman spectroscopy combined with Rietveld analysis. The crystal structures changed from monoclinic structure with P2(1)/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 408 cm(-1) could only be found for compositions with 1:2 long range cation ordering while modes at around 800 cm(-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 A(g) modes at around 800 cm(-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 1:2 short range A(g) mode was observed in all compositions for CNMNT ceramics. The weak A-O hybridization was considered to be the reason for the absence of the 1:1 short range cation ordering. The short range cation ordering was suggested to be appreciably beneficial to the Qf value.