Energy Storage andHarvesting Potential of Eco-FriendlyCa-Substituted Ba_0.8Sr_0.2TiO₃/PVDFFerro-Flexible Composite Films

The eco-friendly lead-free Ba_0.8Sr_0.2TiO₃ ferroelectrics were synthesized by substituting Ca²⁺ on the A site via the conventional solid-state sintering method. Ba_0.8Sr_{0.2–<i>x</i>}Ca_<i>x</i>TiO₃ (<i>x</i> = 0, 0.06, 0.08) ceramics exhibit tetragonal phase formation, as determined from the X-ray diffraction (XRD) pattern. However, partial incorporation of Ca²⁺ at the Ti⁴⁺ site in BSCT08 was confirmed from XRD and supported by scanning electron microscopy (SEM) analysis. The optimum relaxor nature was observed in BSCT06 with a slimmer <i>P–E</i> loop (<i>P</i>_r = 5.25 μC/cm²). The recoverable energy storage density (<i>W</i>_rec) and electrostrictive coefficient (<i>Q</i>₃₃) of BSCT06 were found to be 0.41 J/cm³ and 0.0223 m⁴/C², respectively. The composition BSCT06 was combined with the PVDF polymer via solution casting to fabricate composite thin films for energy harvesting. Characteristic peaks of γ-PVDF with reflections corresponding to the BSCT06 phase were observed from XRD patterns. The composite films demonstrated improved mechanical flexibility through bending and twisting movements; also, the relative permittivity (ε) increased with the addition of the ceramic filler phase in the PVDF matrix. Enhanced breakdown strength (<i>E</i>_b) of 698 kV/cm was found in 10 wt % BSCT/PVDF as compared to BSCT06 ceramic. <i>W</i>_rec of 0.31 J/cm³ with efficiency of 48% was estimated, which strengthened its potential in energy storage applications. Moreover, ceramic-infused PVDF ferro-flexible film was used to fabricate a prototype piezoelectric energy harvester. The highest peak-to-peak voltage of ∼9.3 V and power density of ∼2.86 μW/cm² were obtained for a device using 20 wt % BSCT/PVDF composite film by application of impact force of known value to show its potential in different energy harvesters and sensor applications.