Enhanced performances and in-situ microscopic domain evolution of Cu-doped (Ba0.94Ca0.06)(Zr0.05Ti0.95)O3 ceramic by high-temperature poling

The high-temperature poling strategy (110 °C, 30 kV/cm, 20 min) was imposed on Cu-doped (Ba_0.94Ca_0.06)(Zr_0.05Ti_0.95)O₃ ceramics which had the Curie temperature of 117 °C, to enhance the piezoelectric performances. The high-temperature poled piezoelectric constants d₃₃ and electromechanical coupling factors k_p were 410 pC/N and 0.516, which were enhanced by 17.1% and 15.4%, respectively, higher than that of traditional poled ones. Effects of high-temperature poling on the switching characteristic between non-180° and 180° domains were verified by the intensity ratio of splitting peaks at 2θ around 45°, using the X-ray diffraction analysis. The high-temperature poled samples showed more asymmetric hysteresis loops, with higher internal bias field of 1.8 kV/cm, maximum polarization of 18.5 μC/cm², and residual polarization of 10.7 μC/cm², but lower coercive field of 2.5 kV/cm and smaller positive hysteresis of 1.3%. The high-field piezoelectric constant d₃₃^* showed a pronounced jump of 112.2 pm/V at 110 °C, confirming the optimal poling temperature. The stronger compensating defect dipole field mainly contributed to the asymmetry. And the tiny and easily reversible domains, observed by the in-situ piezoelectric force microscopy, were responsible to the improvement on piezoelectricity.