Polar phonon anomalies in single crystalline TbScO3

TL;DR

This study investigates the polar phonon behavior in TbScO3 single crystals, revealing more active phonons than predicted, phonon softening indicating lattice instability, and an antiferromagnetic transition at low temperatures.

Contribution

It provides new insights into the phonon spectrum and lattice dynamics of TbScO3, highlighting discrepancies with group theory predictions and identifying low-temperature instabilities.

Findings

More polar phonons observed than predicted

Phonon softening indicating lattice instability

Antiferromagnetic transition near 3 K

Abstract

Polarized infrared reflectivity spectra of a (110)-oriented TbScO3 single crystal plate were measured down to 10 K. The number of observed polar phonons active along the crystallographic c axis at low temperatures is much higher than predicted by factor-group analysis for the orthorhombic Pbnm space group. Moreover, the lowest frequency phonons active in E||c as well as in E||[1-10] polarized spectra exhibit dramatic softening tending to a lattice instability at low temperatures. The dielectric permittivity at microwave frequencies does not show any ferroelectric-like anomaly, but the dielectric loss exhibits a maximum at 100 K. The origin of the discrepancy between the number of predicted and observed polar phonons as well as the tendency toward lattice instability are discussed. Magnetic measurements reveal an antiferromagnetic phase transition near 3 K.