Abstract
The temperature and electric field dependences of electrocaloric effect (ECE) of Pb5Ge3O11 (PGO) single crystals, pure and doped with 0.2% of Cr3+ ions, were investigated by the indirect method using the Maxwell relationship. Based on a Maxwell relation, the ECE was characterized via P–T curves under different electric fields. Abnormal ECE with a negative temperature change (ΔT ~ −0.3 K) opposite to that of the normal ferroelectrics was found in the temperature range 390–400 K, several degrees before the phase transition. Normal positive ECE was found around the phase transition point and is of the order of 1.2 for pure PGO and 1.5 for the PGO crystals doped with Cr ions. The abnormal character of ECE originates from electronic conductivity which was detected in the plane perpendicular to the ferroelectric axis. The doping with Cr ion enhances the positive ECE and reduces the negative ECE.
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