Lead-Free Heteroepitaxial (Na_0.8K_0.2)_0.5Bi_0.5TiO₃ Ferroelectric Thin Films Grown by Nd:YAG Pulsed Laser Deposition and Their Applications in Energy Storage and Piezoelectric Sensors

We report on high-performance heteroepitaxial Pb-free ferroelectric thin films of (Na 0.8 K 0.2 ) 0.5 Bi 0.5 TiO 3 (NKBT20), grown for the first time by using a Nd:YAG solid-state laser-equipped pulsed laser deposition setup. The films show a high energy storage density of 26.4 J/cm 3, a high dielectric breakdown strength of >1.9 MV/cm, and an energy storage efficiency of 60.3%. In addition, a very high effective converse piezoelectric coefficient ( d 33 *) of ∼160 pm/V is observed in the films. The enhancement in properties is attributed to the high-quality heteroepitaxial growth of the material achieved through fine-tuned process parameters and to the intrinsically low hysteretic behavior of the relaxor ferroelectric NKBT20 system, which is rarely studied, especially in epitaxial or heteroepitaxial thin film form. This work highlights the potential of the Pb-free NKBT20 system and shows the possibility of using these films for pulsed power applications and piezoelectric sensors/actuators.