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

• Published in: npj computational materials 2023-08, Vol.9 (1), p.154-10, Article 154
• Main Authors: Kim, Kwangrae, Hwang, Woohyun, Oh, Seung-Hyun Victor, Soon, Aloysius
• Format: Article
• Language: English
• Subjects: 639/301/119; 639/301/119/996; Alternative energy sources; Anharmonicity; Approximation; Characterization and Evaluation of Materials; Chemistry and Materials Science; Computational Intelligence; Crystal structure; Density functional theory; Dielectric constant; Dielectric properties; Dielectric strength; Dispersion relations; Dispersions; Electrons; Elementary excitations; Energy; Energy storage; First principles; Lattice vibration; Lead free; Materials Science; Mathematical analysis; Mathematical and Computational Engineering; Mathematical and Computational Physics; Mathematical Modeling and Industrial Mathematics; Perovskites; Phase transitions; Phonons; Potassium niobates; Sodium compounds; Softening; Symmetry; Temperature dependence; Temperature effects; Theoretical; Thermal expansion; Vibrations
• ISSN: 2057-3960; 2057-3960
• DOI: 10.1038/s41524-023-01110-8

Group I niobates (KNbO 3 and NaNbO 3 ) 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 KNbO 3 and NaNbO 3 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.