Positive and negative electrocaloric effect in relaxer ceramic Pb_1-xGd_x(Mg_1/3Nb_2/3)_1-x/4O₃ (x = 0.05)

In last decade since the discovery of the colossal electrocaloric (BC) effect in ferroelectric and relaxor materials showed a possible way of cooling in future. In present work, the electrocaloric (BC) effect in relaxor Pb_1-xGd_x(Mg_1/3Nb_2/3)_1-x/4O₃ for x = 0.05 (denoted as 5Gd-PMN) ceramic synthesized by two step Columbite precursor method is deduced by employing 'indirect method'. The EC effect is determined by calculating the electro caloric temperature change (ΔT_EC) from temperature dependent PE hysteresis loop using thermodynamic Maxwell equation. Temperature dependence of the PE hysteresis loop reveals an anomalous behaviour around ∼ 200 K for 15 kV/cm applied field, which is in the vicinity of a crossover from low temperature negative BC effect to high temperature positive BC effect. This anomaly has been explained evoking dynamics of polar nano-domains against temperature. The maximum value of negative EC coefficient (ξ) for 5Gd-PMN is 0.1 Kmm/kV observed at ∼ 152 K where the polar nano-domains response to external electric field is believed to be sluggish. (author)