Studies On The Regulation And Mechanism Of Electrocaloric Effect Of Relaxor Ferroelectric/Antiferroelectric Thin Films By Interface And Preparation Process

Ferroelectric/antiferroelectric thin films with high performance electrocaloric effect have a potential wide application prospect in chip scale solid-state refrigeration devices.In this paper,the Pb_0.78Ba_0.2La_0.02Zr O₃ relaxor ferroelectric/antiferroelectric thin films were deposited on Pt（111）/TiO_x/SiO₂/Si（100）,La Ni O₃/Pt（111）/TiO_x/SiO₂/Si（100）,La Ni O₃/n-type Ga N and La Ni O₃/p-Type Ga N substrates by using a sol-gel method,and the influence of interface on phase structure and electrocaloric effect of the thin films were analyzed systematically.0.7Pb(Mg_1/3Nb_2/3)O₃-0.3Pb Zr_0.52Ti_0.48O₃ based relaxor ferroelectric thin films near morphotropic phase boundary（MPB）were fabricated on Pt（111）/TiO_x/SiO₂/Si（100）substrate by using a sol-gel method,and the influence of different annealing processes of metal crucible,ceramic crucible,composite of metal crucible and ceramic crucible,composite of ceramic crucible and metal crucible on microstructure and electrocaloric effect also were studied in detail.These results are as follows:（1）The positive electrocaloric effects can be observed at room temperature in the thin films deposited on Pt（111）/TiO_x/SiO₂/Si（100）（abbreviated as Pt）,La Ni O₃/Pt（111）/TiO_x/SiO₂/Si（100）（abbreviated as La Ni O₃/Pt）,La Ni O₃/n-type Ga N（abbreviated as La Ni O₃/n-Ga N）and La Ni O₃/p-Type Ga N（abbreviated as La Ni O₃/p-Ga N）substrates,and temperature variations（ΔT）are 13.08 K,16.46 K,18.70 K and 14.64 K respectively.Furthermore,a negative electrocaloric effect in a broad temperature range（～340 K-440 K）can be obtained in the thin films deposited on La Ni O₃/n-Ga N and La Ni O₃/p-Ga N substrates,andΔT is-3 K.The negative electrocaloric effect is attributed to the process of orthorhombic phase induced by the La Ni O₃/Ga N interface transformed to rhombohedral phase in applied electric field.（2）Compared to x=0.9 component in BaZn_1/3Nb_2/3O₃ doped Pb((Mg_1/3Nb_2/3)_x(Zr_0.52Ti_0.48)_（1-x）)O₃ bulk ceramic system,the ceramic with x=0.7component near MPB have a better electrocaloric effect,and theΔT is 1 K.The thin film with x=0.7 component fabricated by annealing processes of metal crucible,ceramic crucible,composite of metal crucible and ceramic crucible,composite of ceramic crucible and metal crucible display a relatively pure perovskite structure.The largest electrocaloric effect at room temperature was obtained in the thin film fabricated by the metal crucible,and theΔT is 10.2 K.By contrast,a negative electrocaloric effect（ΔT～-0.9 K）in a broad temperature range（300 K-400 K）of the thin film prepared by the ceramic crucible has been achieved.A better negative electrocaloric effect was obtained in the thin films fabricated by the annealing processes of composite of metal crucible and ceramic crucible,composite of ceramic crucible and metal crucible,andΔT are-16.5 K and-2.4 K approximately.The improvement of negative electrocaloric effect comes from the coexistence phase（tetragonal and rhombohedral）structure with higher tetragonal proportion induced by the composite annealing process.