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

Abstract

Here, a phase diagram with phase coexistence near the polycrystalline phase boundary has been studied on $(1\text{\ensuremath{-}}x){\mathrm{AgNbO}}_{3}\text{\ensuremath{-}}x{\mathrm{LiTaO}}_{3}$ 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 ${\mathrm{AgNbO}}_{3}$, 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 $x$ (${\mathrm{LiTaO}}_{3}$) = 0.05, which is the indication of a first-order transition, contributing to the excellent pyroelectric property. Note that the soft mode near 50 ${\mathrm{cm}}^{\ensuremath{-}1}$ is sensitive to reveal the lattice transformation. Moreover, the temperature-dependent optical band gap ( ${E}_{g}$ ) 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 ${\mathrm{AgNbO}}_{3}$ system for designing energy-storage devices.