Abnormal electrocaloric effect of Na0.5Bi0.5TiO3-BaTiO3 lead-free ferroelectric ceramics above room temperature

We demonstrate the electrocaloric effect (ECE) of Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) lead-free ferroelectric ceramics, which were fabricated by the solid-state reaction method. Based on a Maxwell relation, the ECE was characterized via P-T curves under different electric fields. The polarization of NBT increases monotonically within the temperature range of 25-145 degrees C. It indicates that the NBT has an abnormal ECE with a negative temperature change (Delta T-140 = -0.33 K at E = 50 kV/cm) opposite to that of the normal ferroelectrics. The 0.92NBT-0.08BT composition near the morphotropic phase boundary has a normal ECE under low electric fields and an abnormal ECE under high electric fields. The abnormal ECE character originates from the relaxor characteristic between ferroelectric and antiferroelectric phases, while the common ECE is always related to the normal ferroelectric-paraelectric phase transition. (C) 2011 Elsevier Ltd. All rights reserved.