0.2Ti 0.8)O 3-x(Ba 0.7Ca 0.3)TiO 3 ceramics near multi-phase boundary]]>

摘要

AbstractIn this work, the (100-x)Ba(Hf0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3(BHT–xBCT) ferroelectric ceramics were fabricated by a conventional solid-state reaction method. The electrocaloric effect (ECE) of these ceramics was studied by both indirect and direct methods over a wide temperature range with the composition changing from x?=?20 to 50. The most excellent direct ECE occurs in the BHT–50BCT with a good directΔTEC?=?0.27?K (at 92?°C) under the electric field of 10?kV/cm. What's more, the direct EC effect peaks not only locates at near the Curie temperature, but also at the phase-transition temperatures corresponding to the transitions between different ferroelectric phases. In particular, it is found that BHT–50BCT exhibits a direct ECE anomalyΔTEC?=?0.1?K?at 30?°C under an electric field of 10?kV/cm, which can be ascribed to the orthorhombic to tetragonal phase transition, proposing that one can achieve a broad temperature window by tuning the temperature gap between ferroelectric (FE) to paraelectric (PE) boundary and FE-FE boundary. In addition, BHT–30BCT shows good stability of indirectΔTEC,max/ΔEand a broad ECE peak at a higher electric field, indicating that it is possible for electrocaloric temperatureΔTECto be tuned linearly by electric field. Overall, our results imply that the BHT– xBCT ceramics are promising candidates for lead-free cooling refrigeration applications.Highlights?The phase diagram of BHT–xBCT ceramics is established.?An excellent direct ΔTEC,max?=?0.27?K was obtained in BHT–50BCT under 10?kV/cm.?Good stability of indirect ΔTEC,max/ΔE and a broad EC peak was achieved in BHT–30BCT.?Direct EC peaks locates at both the Curie temperature and ferroelectric phase temperatures.?A direct ECE anomaly ΔTEC?=?0.1?K (30?°C) was obtained in BHT–50BCT under 10?kV/cm.]]>