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 (${\Theta }_D=580\mathrm{}$ 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 $\Delta C=0.11\mathrm{}$ cal ${\mathrm{mol}}^{-1\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$. From the specific-heat difference $C_0-C_E$, a soft-mode frequency of 22.9 ${\mathrm{cm}}^{-1\mathrm{}}$ 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.