Flexoelectricity and piezoelectric effects in poly (vinyl alcohol)-SrTiO3 nanocomposites

•PVA-SrTiO3 nanocomposites films with different types of interface layers.•The piezoelectric properties are related to the converse flexoelectric effect.•Maximum of dielectric, mechanical, and piezoelectric properties observed at 40 wt.% of NPs.•Maximum related to the interface layer's contribution. This work investigates the structural, dielectric, mechanical, and apparent piezoelectric properties of PVA-SrTiO3 nanocomposite films by varying the concentration of SrTiO3 nanoparticles. It was shown that the piezoelectric coefficient d33, dielectric constant, elastic modulus, and hardness strongly depend upon nanoparticle concentration; the strong molecular interaction between constituents leads to the formation of an interface layer between PVA matrix and SrTiO3. We propose that the apparent piezoelectric coefficient relates to the converse flexoelectric effect and Maxwell stress induced by an electric field. The proper interface layer formation strongly depends upon nanoparticle concentration; when the concentration increases, their agglomeration drives the destruction of the interface such that the properties of the nanocomposites are diminished. By fine-tuning the interface layer of PVA nanocomposite with nanoparticles functionalizing by polyvinylpyrrolidone, the films exhibit an unexpectedly high apparent piezoelectric coefficient (d33=35 pC/N); this value is higher than neat SrTiO3 crystals and polymer composites with flexoelectric properties. [Display omitted]