Heat capacity of PMN near an electric-field-induced phase transition

The heat capacity of a single crystal of Pb(Mg_1/3Nb_2/3)O₃ (PMN) in an electric filed with E = 3 kV/cm applied along the [111] direction has been measured using adiabatic calorimetry over the temperature range 170–250 K. Anomalies in C _p have been found, which correspond to a field-induced phase transition from a relaxor to a ferroelectric state at 225 K under field cooling conditions or at 235–240 K on the subsequent field heating. The field-induced ferroelectric phase persists in a metastable state at low temperatures and is destroyed on zero-field heating at 210 K. The small entropy change ΔS = 0.028R in the field-induced phase transition suggests an insignificant change in the volume fraction of existing polar nanoregions.