Phase Modulation Of Transition Metal Oxides And The Related Synchrotron Radiation Study

With the development of information technology to low power consumption and integration,the demand for functional oxide materials(especially transition metal oxides)is increasing day by day.While transition metal oxides,as a typical strongly correlated electronic system,have attracted more and more attention due to their rich electrical,optical,magnetic properties and complex coupling transition mechanisms during metal-insulator transition.Especially the strong correlation of d orbital electrons,the transition metal oxide has a very sensitive feedback on the external field,and it often needs to exert a very small interference to trigger its huge metal-insulator phase transition.Therefore,it has important physical significance and considerable application prospect.At present,the research focused function oxide materials are mainly concentrated in vanadium dioxide(VO2)and perovskite rare earth metal nickel oxides(RNiO3).Therefore,several works in this paper are mainly focused on the metal-insulator phase transition of the 3d orbital transition metal oxides in this system.The two classical systems of the 3d orbital transition metal oxides-VO2 and RNiO3(R=rare earth elements):A new method based on water vapor assisted oxidation growth VO2 large size crystalline films is realized.High quality wafer VO2 films were prepared by wet oxidation with water vapor as mild oxidant.The VO2 crystalline films were characterized by synchronous radiation spectroscopy and absorption spectroscopy.The results show that the method can not only obtain uniform and dense pure monoclinic VO2 films,but also very uniform.The resistance of large area films before and after phase transition can reach four order of magnitude jump.Based on the Gibbs free energy in the chemical reaction,the chemical reaction path of vanadium oxidation is calculated,which proves that water vapor can be used as a mild oxidant to achieve the efficient preparation of VO2 films.Effective regulation of VO2 film thickness and strain is achieved through a new strategy of "top-down" wet thinning.The high quality VO2 single crystal epitaxial films with remarkable strain were grown on single crystal TiO2(001)substrates by molecular beam epitaxy.A wet etching technique was used to etch this VO2/TiO2 film with significant interfacial strains.As the etching progresses,their interfacial stresses will relax gradually to obtain ultrathin VO2 films with strain release.The strains release process during the etching process is studied by using synchrotron radiation X ray diffraction reciprocal space imaging technology,and a new way to regulate the interfacial strains of strong strain system VO2/TiO2 epitaxial film is explored.By using the electron-proton synergistic doping effect in metal-acid solution,the controllable hydrogen doping in NdNiO3 films with different crystal plane orientation is realized at room temperature.It is found that different crystal planes have a direct effect on hydrogen concentration.Based on the first principle,the energy band and density of states of the NdNiO3 after hydrogen doping are calculated and the diffusion barrier of hydrogen atoms on different crystal planes is calculated.The experimental observations are reasonably explained.This electron-proton synergistic doping method at room temperature provides a simple hydrogenation method for perovskite RNiO3 oxide systems.Good for promoting perovskite RNiO3 device applications.