Electrocaloric effect in relaxor ferroelectric Ba(Ti1-xYx)O3-x/2 ceramics over a broad temperature range

Crystal structures, dielectric, ferroelectric properties and electrocaloric effects of hetero-valent substituted Ba(Ti1-xYx)O3-x/2 ceramics were studied in the present work. The polar space group of P4mm was adopted based on the Rietveld refinement at room temperature. The diffusivity of phase transition and relaxor behavior are both strengthened by the yttrium substitution. The maximal pyroelectric coefficient decreases, and the extent of corresponding temperature deviated from the dielectric peak temperature to higher temperature increases with increasing the yttrium content. The adiabatic temperature changes and isothermal entropy changes display the same tendencies as those of the pyroelectric coefficients. The Ba(Ti0.944Y0.056)O-2.972 ceramic shows the largest adiabatic temperature change and largest isothermal entropy change among all compositions over a broad temperature range of 50 K. For individual composition, the value of pyroelectric coefficient decreases with increasing the magnitude of applied electric field, and the temperature of maximal pyroelectric coefficient deviates from the dielectric peak temperature to higher temperature. Therefore, the optimal electrocaloric temperature can be adjusted by the magnitude of electric field in relaxor ferroelectricity. (C) 2017 Elsevier B.V. All rights reserved.