Title: Role of phase superposition on the electrocaloric properties in Ba-based ceramics

Abstract

In the last years, there is a high interest in developing alternative cooling technologies because: (i) it is important to reduce greenhouse gases that are used heavily in domestic and industrial refrigeration; (ii) high current densities in integrated circuits impose higher demands on cooling systems that cannot met by the fan-based solutions. The main advantage of electrocaloric (EC) refrigeration is that by comparison with magnetocaloric solid-state refrigerators based on another solid-state cooling technology, the big-sized magnet is still a drawback. BaTiO3(BT) family as EC materials has been studied quite extensively in the past several years in various forms including thin films, bulk ceramics (also multilayer ceramic capacitors -MLCC) and single crystals and a large ΔT has been reported for BT-ceramics in the vicinity of ferroelectric-paraelectric (FE-PE) (tetragonal-cubic T-C) phase transition. Owing to the high transition temperature the using of pure BT as EC materials is limited, but this can be properly modified by incorporation of suitable dopants. In the present paper, we prepared and investigated BaZrxTi1-xO3ceramics with x=0.02; 0.04;0.06;0.08; 0.10;0.12;0.15; 0.175; 0.20. X-ray diffraction data showed the phase purity and SEM images demonstrated homogeneous microstructures (average grain size between 10-5 µm) and well-defined grain boundaries. Impedance spectroscopy in the temperature range of (25 to 150)oC shows a composition-induced ferroelectric-to-relaxor crossover with compositional-dependent shifts of the structural transition temperatures by comparison with ones of the pure BaTiO3.All samples are tunable, DC tunability increasing with x from 2.11 (x=0.08) towards 2.6 (x=0.20) at 25 kV/cm. Polarisation vs. E loops indicate regular variation with increasing Zr addition, a reducing of loop area, remanent and saturation polarization from Psat=15µC/cm2 to Psat=9µC/cm2 and increasing of loop tilting. EC effect was indirect evaluated from P(E) loops with temperature and a maximum of 0.7 K was obtained for x=0.04 at 373K.