Exploring anharmonic lattice dynamics and dielectric relations in niobate perovskites from first-principles self-consistent phonon calculations

Abstract

Group I niobates (KNbO3 and NaNbO3) are promising lead-free alternatives for high-performance energy storage applications. Despite their potential, their complex phase transitions arising from temperature-dependent phonon softening and anharmonic effects on dielectric properties remain poorly explored. In this study, we employ density-functional theory (DFT) and self-consistent phonon (SCP) calculations to investigate finite-temperature phonons in cubic niobate perovskites. To include explicit anharmonic vibrational effects, SCP frequencies are shifted by the bubble self-energy correction within the quasiparticle (QP) approximation, providing precise descriptions of phonon softening in these strongly anharmonic solids. We further calculate the static dielectric constant of KNbO3 and NaNbO3 as a function of temperature using the Lyddane-Sachs-Teller (LST) relation and QP-corrected phonon dispersions. Our theoretical results align with experimental data, offering reliable temperature-dependent phonon dispersions while considering anharmonic self-energies and thermal expansion effects, enhancing our understanding of the complex relations between lattice vibrations and phase transitions in these anharmonic oxides.

Unlocking the key mechanism behind field-induced ferroelectric phase transition in sodium niobate for energy storage systems

“…8,14 Among this class of lead-free AFE materials, sodium niobate (NaNbO 3 ) has emerged as a very strong contender for high performance green energy storage applications. 15–20 Notably, recent reports on NaNbO 3 -based solid solutions have claimed to achieve outstanding energy storage efficiencies. 21–25…”

Pyroelectric Effect in Tetragonal Ferroelectrics BaTiO3 and KNbO3 Studied with Density Functional Theory

“…Instead, other sampling methods such as fitting forces from randomly displaced supercells or molecular dynamics simulations can be used to obtain higher order force constants. Methods to study the phonon anharmonicity and finite-temperature thermodynamics include the temperature-dependent effective potential (TDEP) method, phonon gas model (PGM) with the quasiparticle frequency approach, , iterative self-consistent phonon calculations (SCPH), − and related methods such as self-consistent ab initio lattice dynamics (SCAILD) , and stochastic self-consistent harmonic approximation (SSCHA). , Titanate perovskites BaTiO 3 and SrTiO 3 have been investigated with SCPH and SCPH-based methods, yielding information on phase transitions and finite-temperature phonon dispersions. ,− The anharmonic lattice dynamics of niobate perovskites KNbO 3 and NaNbO 3 have also been investigated using SCPH methods …”

“…38,43−46 The anharmonic lattice dynamics of niobate perovskites KNbO 3 and NaNbO 3 have also been investigated using SCPH methods. 47 Perovskite-structured oxides are a large group of compounds exhibiting many functionalities along with diverse polymorphism of crystal structures and associated phase transitions. Discovery and development of more effective lead-free ferroelectric and pyroelectric alternatives to PZT or lead magnesium niobate Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) have been one of the focus areas in perovskite-related research for past decades.…”