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

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.