Phase diagram with an antiferroelectric/ferroelectric phase boundary in AgNbO3-LiTaO3 energy-storage ceramics by lattice dynamics and electronic transitions

Here, a phase diagram with phase coexistence near the polycrystalline phase boundary has been studied on (1-x)AgNbO3-xLiTaO3 ceramics by analyzing infrared- (IR) and Raman-active phonon dynamics under tuning chemical component and temperature. Optical dielectric functions, ferroelectric domain, and electronic transitions promote the understanding of lattice structure in AgNbO3, and the antiferroelectric (AFE) to ferroelectric (FE) transformation, which results from the joint effect of the cationic antipolar and the oxygen octahedron distortion. The spectroscopic methods of x-ray diffraction, IR reflection, and Raman scattering reveal the mixed phase boundary at x (LiTaO3) = 0.05, which is the indication of a first-order transition, contributing to the excellent pyroelectric property. Note that the soft mode near 50 cm-1 is sensitive to reveal the lattice transformation. Moreover, the temperature-dependent optical band gap (Eg) with the specific electronic transition behavior has been further explored, and becomes complementary evidence for the structural phase transition. This study presents the systematical results on structural properties and optical/dielectric properties for the state-of-the-art AgNbO3 system for designing energy-storage devices.