Effect of excess Bi on the structure and electrical properties of CaBi_2Nb_2O_9 ultrahigh temperature piezoceramics

摘要

CaBi~(2)Nb~(2)O~(9) +  x  wt% Bi~(2)O~(3)( x  = 0, 1, 2, 3) ceramics with bismuth layer structure were prepared by solid state reaction route. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics was investigated. At all compositions, orthorhombic symmetric bismuth layer structure was formed without secondary phases. Excess bismuth caused more uniform grains. The ceramic with excess Bi~(2)O~(3)of 1 wt% exhibited optimal electrical properties as follows: piezoelectric constant d ~(33) = 6.4 pC/N, planar electromechanical coupling coefficient k ~(p) = 11.0%, dielectric constant $$varepsilon _{{33}}^{T}/{varepsilon _0}$$ ε 33 T / ε 0  = 93.5, dielectric loss tan δ  = 0.24%, and resistivity ρ  = 2.9 × 10_(6)Ω cm (@ 500 °C). This ceramic also possess ultrahigh Curie temperature T ~(c) = 940 °C, indicating its potential application for high temperature sensors and actuators.