Preparation And Doping Research Of Perovskite Transition Metal Oxides

Since the 1950 s and 1960 s,transition metal oxides have attracted more and more people's attention due to the unique physical properties.Transition metal oxides with layered perovskite structure gain more popularity because of the varieties of strange physical properties.In addition,it has become a hot research area in both domestic and foreign research groups that to change their physical properties by doping,which will meet the demands of industrial production better.This thesis provides the theoretical reference for the further study on physical properties change by preparing as well as doping high-temperature superconducting compounds YBa2Cu3O7-?(YBCO)and spin-orbit-coupling compounds Sr2IrO4 and studying the changes of the structural characteristics.The author adopts metal organic deposition to prepare YBCO thin film and replaces different substrate and doping Gd3+ and Sm3+ according to one-tenth Y3+ concentration in the pure samples to study the influence of substrate on thin film and doping on the changes of structural characteristics.The results reveal that YBCO crystal grain can't gain crystal growth above the substrate material with the lattice of low matching degree.After doping,YBCO crystal structure produces the slight crystal lattice distortion.Besides,the weakened compressive stress after doping leads to the growth reduction of grain c axis orientation.The author uses solid reaction process to prepare Sr2IrO4 compounds and introduces vacancy defects with the method of absence of Sr doping and uses positron annihilation technique by testing the lifetime of the samples to study the evolution of the relationship between crystal internal defects and doping concentration.The results show that with the increase of absence of Sr doping concentration,the lifetime of positron tends to be shorter.This is because when the doping concentration continues to increase,the slight lattice distortion in the samples leads to the smaller size of vacancy defects so that the lifetime of the defects becomes shorter.When doping concentration reaches a certain degree,the lifetime of positron tends to be longer.This is because new compound defects have been formed due to interaction between part of vacancy defects and residual air bubbles in the samples,which causes larger size and longer lifetime of the defects.At the same time,it also results in the decreasing concentration of defects.The lattice distortion behavior is also evident in XRD diffraction spectrum in the samples,which expresses specifically that each main peaks occur slight deviation along with the increase of doping concentration.