Strong Interface Interaction-Driven Piezoelectric Enhancement in P(VDF-TrFE)/BaTiO₃Composite 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.