Specific heat and electrocaloric properties of a SrTiO3 ceramic at low temperatures

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Abstract
Specific heat data (at zero field and 21.7 kV/cm) and electrocaloric data (field strengths up to 23.5 kV/cm) were measured on the same sample of a carefully prepared SrTiO3 ceramic between 2-30 K. A field-dependent maximum in CT-3 at 23 K is due primarily to a large density of acoustic phonons at 70 cm-1 and to the field induced splitting and hardening of the soft TO mode at low temperatures. A combination of the thermodynamic TdS equation and the Gibbs free energy expansion describes the reversible electrocaloric data very well using the measured specific heat data. The nonlinear Gibbs coefficients ζ and ζ are determined between 8-30 K: ζ has a slight temperature dependence, ζ = 4.73 × 10-14 (T + 15.6) and ζ is constant, 2.96 × 10-21 (cgs units). An irreversible electrocaloric effect occurs in the ceramic, and the unusual temperature dependence of this effect indicates state switching at the large field strengths used.