Structural and electrical properties of K(Ta,Nb)O-3 thin film prepared by sol-gel method for electrocaloric devices

Abstract

This study investigated the structural and electrical properties of thin K(Ta0.6Nb0.4)O-3 films for their applicability to electrocaloric devices. Both of the sol-gel and spin coating methods were used to fabricate thin films. Those sintered at 650 degrees C showed a KTN phase with pyrochlore of K2Ta2O6, but those sintered at 750 degrees C showed pure polycrystalline phase without a pyrochlore phase. The lattice constants observed were a=3.990nm. The dielectric constant rapidly decreased due to decrease in polarization of space charge approximately at an applied frequency of 10 kHz. The dielectric constant and loss at 30 degrees C of the thin films sintered at 750 degrees C were 3,617 and 0.264. The dielectric constant of the specimen sintered at 750 degrees C decreased to about -8.27 %/V according to the applied DC field. The remanent polarization and coercive field at 36 degrees C of the specimen sintered at 750 degrees C were 20.0 mu C/cm(2) and 122.6 kV/cm. When the electric field of 247 kV/cm was applied to the specimen sintered at 750 degrees C, the highest electrocaloric property of 3.02 degrees C was obtained.