Interfacial stress-insensitive tetragonal (Ba,Ca)TiO3-doped BiFeO3 films with superior ferroelectricity and piezoelectricity

Highly desired tetragonal BiFeO3 (BF) films with relatively large polarization are usually realized under large compressive epitaxial strain. Herein, we observed that 0.67BiFeO3–0.33(Ba0.85Ca0.15)TiO3 (BF–BCT) films exhibit a stable tetragonal phase and are insensitive to the interfacial stress induced by in-plane lattice mismatch. The films were grown on three distinct (001)-oriented SrTiO3, LaAlO3, and YAlO3 substrates, each with different in-plane lattice constants. The x-ray diffraction analysis confirmed the tetragonal phase of all BF–BCT films, as indicated by a large tetragonality (c/a) greater than 1.05. All these BF–BCT films demonstrated substantial ferroelectric properties with twice the remnant polarization values (2Pr) of 155–208 μC/cm2, and enhanced piezoelectric behavior with effective piezoelectric coefficients (d33*) of 38–52 pm/V. Meanwhile, all BF–BCT films exhibited high stability with minimal performance degradation under varying frequencies (50 Hz–1 kHz) and thermal cycling (25–100 °C). These findings indicate the BF–BCT films as promising candidates for next-generation multifunctional devices.