Layer-engineered BNBT–polymer films for multifunctional applications

Flexible lead-free piezoelectric composite films were fabricated using a multistep hot-pressing process that combined layers of piezoelectric bismuth sodium titanate-barium titanate and polyvinylidene fluoride copolymers under optimized conditions. This study aims to identify the optimal layer sequence to maximize the dielectric permittivity of the multilayer structure. Structural analysis confirmed the presence of distinct layers in each film, with clear evidence of their interfaces. The polymer layers function as dielectric barriers, redistributing the electric field, reducing local field concentrations at interfaces, and enhancing the material's dielectric strength and reliability. PVDF provides mechanical flexibility and strong insulating properties, whereas P(VDF-TrFE) in the ferroelectric beta-phase exhibits higher dielectric permittivity, improved voltage distribution, and more complete switching of ferroelectric domains in the ceramic layers. The flexible multilayer composites exhibited promising characteristics for both energy storage and energy harvesting, achieving up to 96% energy storage efficiency and generating up to 6 V and approximately 36 mu W of output voltage and power from finger tapping.