Ferroelectric polarization in a centrosymmetric matrix: Local vs. Global phenomena

Composition-dependent phase transition studies play an important role in understanding the structure and properties of the functional materials. In this study, we have investigated the evolution of the crystal structure of the solid solution of antiferroelectric NaNbO₃ with a ferroelectric BaTiO3-based system (Ba_0.9Ca_0.1TiO₃), i.e., (1-x) NN- xBCT for 0 ≤ x ≤ 0.25 using powder X-ray diffraction (HRPXRD) data combined with dielectric studies and Polarization vs Electric field measurements. The X-ray diffraction data helped us to study the distortions in the subcell as well as in supercell by observing the evolution of splitting in the main perovskite reflections and the intensity of weak (superlattice) reflections. We have observed enhancement in physical properties, namely dielectric permittivity and ferroelectric polarization for x=0.10, as a consequence of increased degrees of freedom due to two coexisting ferroelectric phases viz., Pmc21 and Amm2. A long-range centro-symmetric paraelectric phase was revealed using High-resolution x-ray diffraction data for x=0.25. In contrast, Raman spectroscopy reveals a non-centrosymmetric ferroelectric phase at short ranges, suggesting the presence of polar nanodomains in a paraelectric matrix. The correlations among polar nanodomains in a macroscopic paraelectric matrix result in ferroelectric polarization. We believe that this material can act as a potential candidate for multilayer capacitors, energy storage and memory devices.