Comment on "Dielectric behavior of paraelectric KTaO3, CaTiO3, and (Ln_{1/2}Na_{1/2})TiO3 under a dc electric field"

TL;DR

This paper challenges prior claims of polar cluster contributions to dielectric permittivity in KTaO3, showing instead that the permittivity is consistent across low and THz frequencies and can be explained by phonon modes using Landau-Ginzburg-Devonshire theory.

Contribution

It demonstrates that dielectric permittivity in KTaO3 is frequency-independent across a broad range and can be modeled without polar clusters, using Landau-Ginzburg-Devonshire theory.

Findings

Dielectric permittivity at low frequencies equals that in the THz region.

Polar clusters do not significantly contribute to dielectric dispersion.

Landau-Ginzburg-Devonshire theory accurately fits electric field dependence.

Abstract

Chen Ang, Bhalla and Cross [Phys. Rev. B 64, 184104 (2001)] have studied the low-frequency (20 Hz -- 100 kHz) dielectric dispersion of the KTaO3 crystal under a dc electric field. Performing fits of the electric field dependence they came to conclusion that an appreciable contribution to the dielectric permittivity originates from polar clusters. In this Comment we show that the dielectric permittivity at low frequencies (100 Hz -- 1 MHz) equals to that in the THz region, close below the polar phonon response. This excludes the possibility of any appreciable dielectric dispersion due to polar clusters. In addition, we demonstrate that correct treatment using Landau-Ginzburg-Devonshire theory allows to fit the electric field dependence of the dielectric constant without assuming any polarization mechanism besides the polar phonon modes.