| In the positive?negative? electrocaloric effect?ECE?, the application of an electric field results in an increase?decrease? of temperature in ferroelectric thin film under the adiabatic condition. The ECE refrigeration has a good application prospect due to its environmental friendliness and high efficiency. The negative EC E can enhance the cooling efficiency in combination with positive EC E. However, the negative ECE that has been reported is relatively small and the research of it has just started. Therefore, there is a great significance to improve the EC refrigeration efficiency by studying the negative EC E. PbZrO3?PZ? is a kind of typical anti- ferroelectric?AFE? material with large negative ECE strength, but its negative adiabatic temperature change is relative small due to the low breakdown strength in the applied electric field. In order to improve the negative EC effect of PZ AFE thin film, PZ-BMT-BT multilayered thin film was prepared by combining PZ thin film with 0.12Bi?Mg0.5Ti0.5?O3-0.88BaTiO3?BMT-BT? ferroelectric thin film with composite technology. The main works and results are summarized as follows:1. Preparation and the negative ECE of PZ AFE thin filmsThe negative EC E of PZ AFE thin films with different preparation process were explored firstly. The research results show that the negative EC E effect of layer-by- layer annealed PZ AFE thin film is better than that with one-step annealed method. The relative longer annealing time, the better ECE of PZ AFE thin film is.2. The effects of composite mode on negative ECE in PZ-BMT-BT composite ferroelectric thin filmsThe negative EC Es of PZ-BMT-BT multilayered ferroelectric thin films with staggered structure and sandwich structure were studied respectively. The research results show that the negative EC E of PZ-BMT-BT multilayered thin film has been greatly improved compared with PZ AFE thin film. The PZ-BMT-BT multilayered ferroelectric thin film with staggered structure has a better negative ECE than other thin films.3. The effects of annealing method on negative ECE staggered structure PZ-BMT-BT composite ferroelectric thin filmsTo further improve the negative ECEs through improving the annealing methods of staggered structure PZ-BMT-BT composite ferroelectric thin films. The experimental results show that the negative ECE of staggered structure PZ-BMT-BT multilayered ferroelectric thin film prepared by one-step annealed method is better than that with layer-by- layer annealed method. With increasing annealing time, the negative ECE of PZ-BMT-BT composite ferroelectric thin films is increased and then decreased. The relative large negative EC E appears in the annealing time of 10 min with DT =-32 K under the electric field DE=1151 kV×cm-1, so the EC strength can reach to 0.0278 K×cm×kV-1, which is 1-2 orders magnitude higher than that in other PZ-BMT-BT multilayered ferroelectric thin films. |
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