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 °C. It indicates that the NBT has an abnormal ECE with a negative temperature change (ΔT140 = −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.

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► Na0.5Bi0.5TiO3 has abnormal electrocaloric effect (ECE) with negative entropy change opposite to the common ferroelectrics.
► 92NBT–8BT near morphotropic phase boundary has normal ECE under low electric field and abnormal ECE under high field.
► The abnormal ECE originates from the relaxor characteristics between ferroelectric and antiferroelectric phases.