The field induced e_31,f piezoelectric and Rayleigh response in barium strontium titanate thin films

The electric field induced e_31,f piezoelectric response and tunability of Ba_0.7Sr_0.3TiO₃ (70:30) and Ba_0.6Sr_0.4TiO₃ (60:40) thin films on MgO and silicon was measured. The relative dielectric tunabilities for the 70:30 and 60:40 compositions on MgO were 83% and 70%, respectively, with a dielectric loss of less than 0.011 and 0.004 at 100 kHz. A linear increase in induced piezoelectricity to -3.0 C/m² and -1.5 C/m² at 110 kV/cm was observed in Ba_0.6Sr_0.4TiO₃ on MgO and Ba_0.7Sr_0.3TiO₃ on Si. Hysteresis in the piezoelectric and dielectric response of the 70:30 composition films was consistent with the positive irreversible dielectric Rayleigh coefficient. Both indicate a ferroelectric contribution to the piezoelectric and dielectric response over 40-80 °C above the global paraelectric transition temperature.