Nonlinear ferroelectric characteristics of barium titanate nanocrystals determined via a polymer nanocomposite approach.

The growing demand for high energy storage materials has garnered substantial attention towards lead-free ferroelectric nanocrystals (NCs), such as BaTiO 3 (BTO), for next-generation multilayer ceramic capacitors. Notably, it remains challenging to accurately measure the dielectric constant and polarization-electric field ( P - E ) hysteresis loop for BTO NCs. Herein, we report on nonlinear ferroelectric characteristics of BTO NCs via a polymer nanocomposite approach. Specifically, poly(vinyl pyrrolidone) (PVP)/BTO nanocomposite films of 3-10 μm thickness, containing 380 nm tetragonal-phased and 60 nm cubic-phased BTO NCs with uniform particle dispersion, were prepared. Theoretical deconvolution of the broad experimental P - E loops of the PVP/BTO NC composite films revealed three contributions, that is, the linear deformational polarization of the nanocomposites, the polarization of BTO NCs ( P p ), and the polarization from strong particle-particle interactions. Using different mixing rules and nonlinear dielectric analysis, the overall dielectric constants of BTO NCs were obtained, from which the internal field in the BTO NCs ( E p ) was estimated. Consequently, the P p - E p hysteresis loops were obtained for the BTO380 and BTO60 NCs. Interestingly, BTO380 exhibited square-shaped ferroelectric loops, whereas BTO60 displayed slim paraelectric loops. This work presents a robust and versatile route to extract the P p - E p loops of ferroelectric NCs from polymer/ceramic nanocomposites.