Study On The Preparation And Dielectric Tunable Properties In Pb(Sc_1/2X_1/2)O₃（X=Nb/Ta）-Based Thin Films

High dielectric tunable ferroelectric thin film materials have potential applications in radars,5G/6G mobile communications and other civil and military communication systems.In this thesis,the Pb(Sc_1/2Nb_1/2)_0.9(Mg_1/3Nb_2/3)_0.1O₃（PSNMN）relaxor ferroelectric thin films were deposited on Pt（111）/Ti Ox/Si O₂/Si（100）（Pt）substrate by sol-gel method,and the effect of annealing conditions on the dielectric tunability performance was studied systematically.Meanwhile,Pb(Sc_1/2Ta_1/2)O₃（PST）relaxor ferroelectric thin films were prepared on Pt substrate and La Ni O₃/Pt composite substrate by this method,and the effect of La Ni O₃ buffer layer on dielectric tunability performance was investigated.In addition,energy storage performance was also studied.These results are as follows:（1）Through the control of annealing atmosphere and annealing time,the dielectric tunability of as-prepared PSNMN thin films,annealed in air for 5 h,10h,and 15 h,annealed with atmosphere-compensating-block（ACB）for 10 h,15 h and 20 h at 530 k V/cm and 10 k Hz was～47.0%,～46.5%,～48.5%,～46.8%,～76.4%,～80.0%and～77.3%,respectively.The enhanced dielectric tunability of annealed with ACB of PSNMN thin films could be ascribed to the weaker domain-pinning effect by oxygen vacancy.Meanwhile,the PSNMN thin films annealed with ACB also exhibited an extremely high thermally-stable dielectric tunability in an ultra-broad temperature range（>130 K）,which could be benefited from the Maxwell-Wagner（MW）effect generated by the interface between the PSNMN disordered matrix and the B-site nanoscale-ordered structure which is formed during the long-term annealing process.Moreover,the dielectric loss of PSNMN thin films annealed with ACB can be sharply reduced by more than an order of magnitude,from～0.50 of the as-prepared thin film to～0.037 of the thin film annealed with ACB for 15 h at 1 k Hz,which is mainly attributed to the lower concentration of oxygen vacancy and the possible MW effect.In addition,the recoverable energy density（increasing from～22.3 J/cm³ of the as-prepared thin film to～27.2 J/cm³ of the thin film annealed with ACB for 15 h）,energy storage efficiency（increasing from～47.0%of the as-prepared thin film to～75.1%of the thin film annealed with ACB for 15 h）and thermal stability of PSNMN thin films annealed with ACB were also significantly improved.For dielectric tunability and energy storage performance of ferroelectric thin films,in addition to the important effect of annealing conditions,substrate types on the performance of thin films cannot be underestimated.Therefore:（2）The dielectric loss of PST thin film deposited on Pt substrate is larger than that deposited on La Ni O₃/Pt composite substrate,which may be that there are many internal defects in the PST thin film deposited on Pt substrate,which lead to large leakage current of the thin film and increase of dielectric loss.The dielectric tunability of PST thin film deposited on Pt substrate is～27.2%at its maximum safe electric field（～240 k V/cm）,while that of PST thin film deposited on La Ni O₃/Pt substrate is～56.6%at its maximum safe electric field（～492k V/cm）,which may be due to the smaller leakage current of PST thin film deposited on La Ni O₃/Pt substrate.In addition,after adding La Ni O₃ buffer layer,the recoverable energy density and energy storage efficiency of the PST thin film were effectively improved,and the frequency stability of the thin film was also improved.