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

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.