Flexible and lightweight polymer-ceramic composites are actively pursued for mechanical energy harvesting applications. In this work, polyvinylidene fluoride (PVDF)-based composite films incorporating sol-gel synthesized (Ba,Ca)(Sn,Ti)O3 (BCST; Ba0.91Ca0.09Sn0.08Ti0.92O3) ceramic fillers were fabricated using a cost-effective solution-casting method and systematically investigated. Transmission electron microscopy (TEM) confirmed BCST particle sizes in the range of 300–600 nm. Multiscale characterization revealed a significant role of filler–polymer interfacial interactions in governing the functional properties. Microstructural and spectroscopic analyses indicate that BCST particles act as heterogeneous nucleation centers, promoting the formation of electroactive β- and γ-phases in PVDF. The composite films exhibited enhanced dielectric permittivity while maintaining low dielectric loss, governed by dipolar and interfacial polarization mechanisms. Macroscopic ferroelectric and piezoelectric properties enhanced with BCST content, with maximum polarization (Pmax) and piezoelectric charge coefficient d33 reaching a value of ~3.8 μC/cm2 and ~ 22 pC/N, respectively, for the composite with a filler concentration of 10 wt%. Nanoscale switching and piezoelectric activity were confirmed using piezoresponse force microscopy (PFM). Nanoindentation measurements revealed increased hardness and modulus, indicating improved mechanical robustness due to BCST incorporation. Under low-frequency bending excitation at a resonance frequency of ~4.4 Hz, the cantilever-beam-type energy harvester delivered a maximum output voltage of ~0.83 V and a volumetric power density of ~0.75 μW/cm3 for the composite with 10 wt% BCST. These results demonstrate that BCST is an effective lead-free ferroelectric filler for enhancing the functional properties of PVDF–BCST polymer composites, highlighting their potential for low-frequency, low-power energy harvesting applications.
