Strong Interface Interaction-Driven Piezoelectric Enhancement in P(VDF-TrFE)/BaTiO3 Composite Sensors and Their Low-Frequency Applications

Flexible piezoelectric sensors offer excellent wearability and easy integration, making them attractive for smart devices and health monitoring. However, their low piezoelectric coefficient (d33) limits widespread use. In this study, surface-coated barium titanate nanoparticles (mBT) with a core–shell structure were synthesized and incorporated into P(VDF-TrFE) to form composite films. The film containing 10 wt % mBT showed a dielectric constant of 20 at 103 Hz, a 31% increase in residual polarization (7.82 μC·cm–2), a 30% reduction in coercive field (40 MV/m), and a 58% enhancement in quasi-static d33 (41 pC/N) compared with the pure polymer. These improvements arise from enhanced interfacial interactions and phase compatibility due to the mBT core–shell design, which promotes β-phase formation in the polymer matrix. A flexible sensor fabricated from the optimized composite displayed superior pressure sensitivity and linearity (R2 > 0.999). Its dynamic d33 and voltage coefficient (g33) reached 42 pC/N and 244 mV·m/N, improving by 66% and 35%, respectively. The sensor accurately detected low-frequency vibrations (0.5–50 Hz), highlighting the potential of core–shell nanoparticle modification for developing high-sensitivity, low-frequency flexible piezoelectric sensors.