Sequence of structural transitions and electrocaloric properties in (Ba1-xCax)(Zr0.1Ti0.9)O-3 ceramics
Résumé
The influence of the incorporation of Calcium in lead-free ferroelectric Ba(Zr0.1Ti0.9)O-3 perovskite on its structural phase transition, dielectric, pyroelectric, ferroelectric, and electrocaloric effect was investigated. Room temperature X-ray diffraction study allowed the identification of a continuous solid solution in the composition range 0 <= x <= 20 mol% with a rhombohedral to orthorhombic structural transition beyond 15mol%. Structural investigation of X-ray diffraction as a function of temperature reveals four different structural regions for the compositions with low content of Ca and three regions for the compositions with high Ca-content. Using heat flow measurements and dielectric investigations, two sequences of structural phase transitions were elucidated. The tetragonal-to- orthorhombic and orthorhombic-to-rhombohedral phase transitions induced by temperature variation were found to decrease with the increase of the Ca2+ content, while the cubic-to-tetragonal phase transition temperature remained almost unchanged and exhibited a dielectric permittivity maximum observed around the composition of x = 15mol%. The electrocaloric temperature change Delta T was calculated from two methods: the thermal variation of P-E hysteresis loops and pyroelectric current. The highest electrocaloric Delta T/DE = 0.24 K mm/kV was found for the composition x = 0.05. The largest electrocaloric responsivity around 0.30 K mm/kV was observed for this composition at Curie temperature using direct method. (C) 2017 Elsevier B.V. All rights reserved.