Preparation And Properties Of Several ABO₃-type Ferroelectric Thin Films

In this thesis,perovskite Lead Zirconate Titanate ferroelectric thin films and Bismuth Ferrite multiferroic thin films were prepared by Sol-gel method.The phase structure,microstructure,dielectric and ferroelectric properties and optical properties of these films were studied.In addition,the ferromagnetic electrode,Lanthanum Strontium Manganate thin films were prepared by Pulsed Laser Deposition.The crystal structure,surface morphology,ferromagnetic properties and electrical transport properties were studied.Perovskite structure PbZr_0.52Ti_0.48O₃ ferroelectric thin films were successfully prepared on LaNiO₃/Si substrates by Sol-gel method.The films were annealled by muffle furnace and hot plate at 550°C for 30min,respectively.The thin films under different annealing conditions were analyzed by X-ray diffraction,dielectric spectrum,P-E hysteresis loop,leakage current density and C-V curves.The results show that higher crystallinity and better electrical properties of thin films annealed on hot plate than those annealed on Mafer furnace.The thin films annealed on hot plate have higher dielectric constant and moderate dielectric loss and better hysteresis loop with residual polarization of 36.4μC/cm² and coercive field of 168kV/cm.PbZr_0.52Ti_0.48O₃ ferroelectric thin films were spined on FTO substrate by sol-gel method,and then annealed on hot plate at 550°C.With the increase of annealing time from 2 min to 40 min,the pyrochlore phase gradually changes to perovskite phase.The thin films have good transmittance in the visible light range.With the increase of annealing residence time,the optical band gap of the thin films becomes wider.When the annealing time increases from 2 min to 40 min,the dielectric constant and the residual polarization value increase,however when the annealing time of 60 min,the dielectric constant and the residual polarization value decrease slightly.The residual polarization value of the films annealed for 40min is 40.3μC/cm²,and the coercive electric field is 228 kV/cm.Pb_0.82La_0.12Zr_0.85Ti_0.15O₃ thin films and Pb_0.82(La_0.6Bi_0.4)_0.12Zr_0.85Ti_0.15O₃ films were prepared on FTO substrates by sol-gel method.The films were annealed at different temperatures in a rapid annealing furnace for 30 min.With the increase of annealing temperature from 580°C to 670°C,there are fewer pyrochlore phases and more perovskite phases in Pb_0.82La_0.12Zr_0.85Ti_0.15O₃ films.While the annealing temperature of Pb_0.82(La_0.6Bi_0.4)_0.12Zr_0.85Ti_0.15O₃ films increases to 600°C,the pyrochlore phase in the film almost disappeared.When the temperature reaches 650°C,the XRD of perovskite phase and pyrochlore phase becomes stronger at the same time,that is,the crystallinity of perovskite phase and pyrochlore phase is higher.Compared with the dielectric and ferroelectric properties of the films doped with 4.8%Bi ion and undoped Bi ion,it indicates Bi doping is a good method to reduce the annealing temperature of Pb_0.82La_0.12Zr_0.85Ti_0.15O₃ thin films.BiFeO₃ thin films were prepared on FTO substrates by sol-gel method.The effects of Mn doping on the structure,ferroelectric,ferromagnetic and optical properties of BiFeO₃ films were investigated.The results show that Mn doping can inhibit the formation of impurity phase,decrease the grain size,inhibit the increase of Fe²⁺and change the mechanism of leakage conduction.The high residual polarization value of27μC/cm² was obtained in BiFe_0.95Mn_0.05O₃ thin films.In addition,Mn doping improves the magnetic properties and decreases the optical band gap.The development of narrow optical band gap doped BiFeO₃thin films in the field of photocatalysis and photovoltaic has broken new ground.LSMO thin films were deposited on（100）SrTiO₃ substrate by PLD at different deposition times as bottom electrodes.The results show that with the increase of deposition time,the roughness of the samples increases first and then decreases,but the magnetization increases steadily.Through the analysis of hysteresis loop and electric transport properties,the sample deposited with 5 min has the best properties,but the roughness is too large to be used as electrode.The surface roughness of the sample deposited with 2min is small,but the performance is not very good,so it can be used as electrode material.