Dielectric and dynamical properties of ABO3 (A = Li, Na; BV, Nb): A comparative first-principles study

To enhance the understanding of the characteristics and underlying microscopic physics of ferroelectric and hyperferroelectric instabilities in the trigonal structure of LiNbO₃-type oxides, we performed a comparative study of the lattice dynamical properties of LiNbO₃, LiVO₃, and NaVO₃ using first-principles computations. The behavior of both instabilities under increasing hydrostatic pressure is also investigated. The calculated dielectric constants (ε_∞) are 6.81 for LiNbO₃, 16.00 for LiVO₃, and 14.60 for NaVO₃, highlighting the significant impact of B-site cation substitution on the dielectric response of these compounds. The calculated phonon dispersion curves reveal the dependence of ferroelectric instabilities on A and B cation substitutions. Under hydrostatic pressure, ferroelectricity is consistently enhanced, unlike perovskites such as BaTiO₃. Via the analysis of the real-space interatomic force constants, we show that the difference in the phonon dispersion arises from the change in the A on-site IFC and the cation-oxygen IFCs, which further drives the change of the dynamics under pressure. This study offers insights into the tunability of hyperferroelectricity in LiNbO₃-type materials.