Specific heat and electrocaloric properties of KTaO3at low temperatures

Abstract

Specific-heat data (at zero field and 15.6 kV/cm), dielectric data, and electrocaloric data measured on a KTa${\mathrm{O}}_{3}$ crystal between 2 and 25 K are reported. The zero-field specific heat is about 30 times larger than the Debye prediction (${\ensuremath{\Theta}}_{D}=580$ K) at these temperatures but shows no anomaly characteristic of a sharp phase transition as suggested by the neutron data. A very broad transition is possible around 10 K for which $\ensuremath{\Delta}C=0.11$ cal ${\mathrm{mol}}^{\ensuremath{-}1}$ ${\mathrm{K}}^{\ensuremath{-}1}$. From the specific-heat difference ${C}_{0}\ensuremath{-}{C}_{E}$, a soft-mode frequency of 22.9 ${\mathrm{cm}}^{\ensuremath{-}1}$ is determined near 10 K. The electrocaloric effect consists of reversible and irreversible components. The reversible effect is in good thermodynamic agreement with the specific-heat and dielectric data and with published data on the Gibbs free-energy coefficients. Both the irreversible effect and the dielectric data indicate that KTa${\mathrm{O}}_{3}$ does not retain a center of symmetry at low temperatures.