Structural, electrical and piezoelectric properties of V-, Nb- and W-substituted CaBi4Ti4O15 ceramics

Abstract

The equimolar substitution of V5+, Nb5+ and W6+ ions in the B-site of CaBi4Ti4O15 (CBT) ceramics was performed, and their sintering characteristics and microstructures were investigated. The results indicated that V2O5 has a substantial effect on the structure and properties of CaBi4Ti4O15 ceramics compared to Nb2O5 and WO3. The V-substituted sample exhibited the lowest sintering temperature, the best sinterability and the lowest conductivity among all of these samples. The comparative Raman study of the V5+, Nb5+ and W6+ doping indicated that the Bi ions in the [Bi2O2]2+ layers are more stable than those at the A sites in the pseudo-perovskite blocks, and the volatilisation of Bi during sintering preferentially occurs at A sites in the pseudo-perovskite blocks. The decrease in the volatilisation of Bi in the V-doped sample helps to maintain the amount of Bi atoms in the pseudo-perovskite blocks and the stoichiometric composition of the ceramics resulting in excellent properties. In addition, the increase in Bi ions in the pseudo-perovskite structure and the dense microstructure with a closed-packed arrangement of small grains, which result from sintering of the ceramics at a low temperature, also contributed to the notable reduction in the electrical conductivity. In comparison to the Nb- and W-doped CBT ceramics, the V-doped samples exhibited a dual slope transition in the conductivity-temperature curves, a minimum conductivity over the measured temperature range and optimum piezoelectric properties.