In this study, KTN heterolayer thin films were fabricated by alternately stacking films of K(Ta_0.70Nb_0.30)O₃ and K(Ta_0.55Nb_0.45)O₃ synthesized using the sol-gel method. The sintering temperature and time were 750℃ and 1 hour, respectively. All specimens exhibited a polycrystalline pseudo-cubic crystal structure, with a lattice constant of approximately 0.398 nm. The average grain size was around 130~150 nm, indicating relatively uniform sizes regardless of the number of coatings. The average thickness of a single-coated film was approximately 70 nm. The phase transition temperature of the KTN heterolayer films was found to be approximately 8~12℃. Moreover, the 6-coated KTN heterolayer film displayed an excellent dielectric constant of about 11,000. As the number of coatings increased, and consequently the film thickness, the remanent polarization increased, while the coercive field decreased. The 6-coated KTN heterolayer film exhibited a remanent polarization and coercive field of 11.4 μC/cm² and 69.3 kV/cm at room temperature, respectively. ΔT showed the highest value at a temperature slightly above the Curie temperature, and for the 6-coated KTN heterolayer film, the ΔT and ΔT/ΔE were approximately 1.93 K and 0.128×10^-6 K·m/V around 40℃, respectively.

In this work, the (K_1-xAg_x)(Ta_0.8Nb_0.2)O₃ (x=0.1-0.4) ceramics were fabricated using mixed-oxide method, and their structural and electrical properties were measured. All specimens represented a pseudo cubic structure with the lattice constant of 0.3989 nm. When 0.4 mol of Ag was added, second phases induced from metallic Ag and K₂(Ta,Nb)₆O₁₆ phase were observed. Dielectric constant and dielectric loss of K(Ta_0.8Nb_0.2)O₃ specimen doped with 0.3 mol of Ag were 2,737 and 0.446, respectively. The curie temperature was about -5℃, which does not change with Ag addition. The remanent polarization began to decrease sharply around 12~15℃, and the temperature at which the remanent polarization began to decrease as the applied voltage increased shifted to the high temperature side. The electrocaloric effect (ΔT) and electrocaloric efficiency (ΔT/ΔE) of the (K_0.7Ag_0.3)(Ta_0.8Nb_0.2)O₃ ceramics were 0.01024℃ and 0.01825 KmV^-1, respectively.

Heterolayered K(Ta,Nb)O₃/Pb(Zr,Ti)O₃ thin films on Pt/Ti/SiO₂/Si substrates were prepared by a sol-gel process and spin-coating method. The structural and electrical properties were measured to investigate the possibility of application as an electrocaloric effect device. All specimens exhibited dense and uniform cross-sectional structures without pores, and the average thickness of the specimen coated six times was approximately 394 nm. Curie temperatures were observed at 5℃ or less in type-Ⅰ and 10℃ in type-Ⅱ specimens, respectively. Type-Ⅱ specimens coated 6 times showed a relative dielectric constant of 758 and remanent polarization of 9.71 μC/cm₂ at room temperature. The maximum electrocaloric effect occurred between 20 and 25℃, slightly higher than their Curie temperature, and the electrocaloric property (ΔT) of the type-Ⅱ specimens coated 6 times was approximately 1.2℃ at room temperature.

The electrocaloric effect in 0.94(Bi_0.5Na_0.5)TiO₃+0.06KNbO3+0.9 wt% G.F.ferroelectricceramics was observed in terms of the temperature change (ΔT) of the fabricated ceramics, Curie temperature Tc, and applied electric field. The specimens were fabricated by a conventional solid-state reaction. T_c appeared near 165∼170℃. The P-E hysteresis showed a tendency to slim down with a temperature increase and finally was slimmest near 150℃. With the increase of temperature, the polarization revealed a gradual decrease, and a sharp decline near T_c. When an electric field of 45 kV/cm was applied, the largest polarization was shown. The maximum value of the temperature change (ΔT=0.31℃) was obtained at 165℃ under an applied electric field of 45 kV/cm.

In this study, in order to develop composition ceramics for refrigeration device application, Ba(Ti_0.9Zr_0.1)O₃ composition was fabricated using conventional solid-state method. Electrocaloric effect of this ceramic was investigated using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to 150℃. Curie temperature of Ba(Ti_0.9Zr_0.1)O₃ ceramics showed 80℃. The maximum value of ?T = 0.12℃ in ambient temperature of 115℃ under 30 kV/cm was appeared. It is concluded that Ba(Ti_0.9Zr_0.1)O₃ ceramics can be applied as refrigeration device application.

In this study, in order to develop relaxor ferroelectric ceramics for refrigeration device application with large electrocaloric effect and low sintering temperature, PLZT(8/65/35) ceramics was fabricated using conventional solid-state method with the variation of sintering temperature (1,050℃, 1,100℃, 1,200℃). The XRD pattern of all specimens indicated general perovskite structure with secondary phase. From the results of temperature dependence of dielectric constant, the TC (ferroelectric-paraelectric phase transition temperature) was shifted toward high temperature with increasing sintering temperature. When the specimen was sintered at 1,100℃, the optimal value of .T ∼0.349℃ in ambient temperature of 215℃ was appeared. It is considered that PLZT(8/65/35) ceramics possess the possibility of refrigeration device application.

In this study, in order to develop relaxor ferroelectric ceramics for refrigeration device application with large electrocaloric effect, PLZT(8/65/35) composition was fabricated using conventional solid-state method. The Curi temperature of this composition PLZT ceramics was 230℃, and the P-E hysteresis loops of the PLZT ceramics as a fuction of temperature became slim by degrees with higher temperatures. The maximum value of .T of 0.243°C in ambient temperature of 215°C with 30 kV/cm was appeared. It is considered that PLZT ceramics possess the possibility of refrigeration device application.

In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, 8/65/35 PLZT ceramics were fabricated by the conventional solid-state method with the addition of Bi2O3, CuO, Li2CO3 and the variation of sintering temperature from 930℃ to 990℃. The XRD pattern of all specimens indicated general perovskite structure and the rhombohedral phase were observed. Curie temperature (Tc) of all specimens was observed in the vicinity of about 190℃. Density, coercive field and remnant polarization of the specimen sintered at 950℃ was 7.55 g/cm3, 8.895 kV/cm, 11.22 μC/㎠, respectively. EC effect of PLZT ceramics was measured by indirect method and the temperature change ΔT due to the electrocaloric effect was calculated by Maxwell’s relations. ΔT of ceramic sintered at 950℃ was 0.21℃ under application of 40 kV/cm at 190℃.

In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, (Pb0.88La0. 08)(Zr0.65Ti0.35)O3 ceramics were fabricated by the conventional solid-state method. Electrocaloric effects of (Pb0.88La0.08)(Zr 0.65Ti0.35)O3 ferroelectric ceramics were investigated and discussed using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to 220 . The temperature change ΔT due to the electrocaloric effec t was calculated by Maxwell’s relations, and reached the maximum of 0.19 at 190 under applied electric field of 30 kV/cm.

In this work, in order to develop the ceramics with an excellent electrocaloric effect, [Bi0.5(Na0.84K0.16)0.5]TiO3 ceramics were fabricated by conventional solid state reaction method. The ceramics was observed as rhombohedral phase by X-ray diffraction patterns. To investigate the electrocaloric effect of the ceramics, P-E hysteresis loops were measured at various temperature. The temperature change ΔT of these ceramics was calculated using the Maxwell``s relations. The maximum value of temperature change ΔT was obtained as 0.3 1℃ at 165℃ under applied electric fields 45 kV/cm.