Research On The Microstructure And Electrical And Magnetic Properties Of Perovskite Oxide Films

Perovskite oxide films are widely used in people's daily life because of their uniquephysical properties.The study of the microstructure and physical properties of perovskite oxide films will provide theoretical guidance for adjusting the film performance and serving the human society.In this thesis,the microstructure of perovskite oxide films was investigated by the transmission electron microscopy?TEM?,and was further correlated with their physical properties.In chapter 1,the crystal structure and theoretical ideas about the perovskite oxide were generally given.First,the crystal structure and electronic structure were introduced.Then,we discussed some theoretical models of perovskite films.The preparation of specimens for transmission electron microscopy?TEM?examinations was briefly described.In the end,the research purposes and significance of our work were given.In chapter 2,the preparation and microstructure characterization of perovskite oxide films were described.Besides,the experimental equipment was also introduced.In chapter 3,the effect of buffer layer and film thickness on the microstructure and growth mode of La_0.67Ca_0.33MnO₃ films was investigated by TEM.The buffer layer can prevent the penetration of the pre-existing dislocations and the formation of new dislocations,thus reducing the dislocations.The LCMO films transform from a layer-by-layer growth mode to a layer by layer plus an island?columnar?growth mode with increasing the film thickness.A growth model was introduced to explain the effect of LMO buffer layer and film thickness on the growth mechanism of LCMO films.The results can shed light on the growth mechanisms for other perovskite epitaxial films with buffer layers.In chapter 4,the magnetic and transport properties of La_0.9Sr_0.1CoO₃ films were investigated.The change in the magnetic properties of films was attributed to the lattice strain,which can affect the spin state of Co ions.The resistivity was inversely proportional to the film thickness.The electrical transport mechanism of the film transformed from a three-dimensional variable range hopping?VRH?to a small-polaron hopping conduction?SPC?with increasing temperature.And the temperature of transport mechanism transformation decreased gradually with increasing film thickness.In chapter 5,the effect of lattice strain on the transport properties of LSMO film was investigated.It was found that the resistivity upturn only occurred in LSMO films with small lattice mismatch.For the monolayer,the resistivity upturn of LSMO film with small mismatch was caused by the weak localization effect.While the resistivity upturn of LSMO multilayers with small mismatch was caused the Kondo effect.