Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi_0.5Na_0.84K_0.16TiO₃)–0.04SrTiO₃ (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x = 0.0175, a large-signal piezoelectric coefficient (S_max/E_max = d₃₃*) of 735 pm V⁻¹ at 6 kV mm⁻¹ was observed at room temperature. Interestingly, at a higher temperature of 110 °C, the sample still showed a large d₃₃* of 570 pm V⁻¹. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285 m⁴ C⁻² over the temperature range of 25–170 °C. Moreover, the energy density for x = 0.030 sample was ∼1.0 J cm⁻³ with an energy storage efficiency of ˃70% in the temperature range of 25–135 °C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.