Structural, dielectric, ferroelectric, and electrocaloric properties of 2% Gd_2O_3 doping (Na_(0.5)Bi_(0.5))_(0.94)Ba_(0.06)TiO_3 ceramics

摘要

Structural, dielectric, and ferroelectric properties, and electrocaloric effects of pure and Gd doped (Na_(0.5)Bi_(0.5))_(0.94)Ba_(0.06)TiO_3 ceramics prepared by the conventional solid-solid method have been carried out. The X-ray diffraction analysis confirms a pure perovskite structure with the coexistence of tetragonal and rhombohedra structures in both powders. The thermal and frequency dependences of the dielectric constants of both ceramics revealed relaxor behavior. The two compounds exhibited two phase transitions: ferroelectric/antiferroelectric (FE/AFE) transition followed by an anti-ferroelectric/paraelectric (AFE/PE) transition at higher temperatures. Remarkably, we noticed that the small amount of Gd doping (2%) highly enhanced the dielectric properties of the parent compound by about 71%. The phase diagram was as well influenced by the Gd doping, where the FE/ AFE transition temperature rose from 90 in the parent compound to 115℃ in the doped one whereas the AFE/PE transition temperature was decreased from 320 to 270 ℃, respectively. The direct electrocaloric measurements performed on both compounds showed that the ferroelectric/ antiferroelectric phase transition was accompanied by a significant electrocaloric effect. The Gd~(3+) doping improved the electrocaloric properties of the parent compound, where a remarkable temperature variation of 1.4 K was obtained in the doped ceramic. The results of the direct electrocaloric measurements will be compared and discussed with those derived from the indirect method.