The Studies Of The Preparations Of Molybdenum Lithium Oxides Containing Mo₃ Clusters And Their High Pressure Properties

Molybdenum lithium oxides are a kind of efficient anode materials for rechargeable lithium-ion batteries.And they can overcome the shortcomings of normal metal oxides as LIBs anode materials,that is,poor conductivity,agglomeration,capacity attenuation,etc.Therefore,it has attracted much attention because of their different composition and structure leading to unique properties.Pressure is an effective means to control the physical and chemical properties of materials.The combination of high-pressure technique and other experimental methods makes it possible to explore the new physical properties of molybdenum lithium oxides under high pressure.In this thesis,the parent Li₂MoO₄,and its derivative compounds Li₂AMo₃O₈（A=In,Sc）,and LiScMo₃O₈ were prepared by traditional solid state synthesis and high-temperature and high-pressure synthesis respectively.The above samples were subjected to conventional X-ray diffraction,Raman spectroscopy,and fluorescence spectroscopy.And using high-pressure in-situ Raman measurements to study the lattice vibration of the prepared samples under high pressure,and the obtained results are as follows:1)The crystal structure and luminescence properties of Li₂MoO₄ have been studied by using powder X-ray diffraction,high pressure Raman and fluorescence spectroscopy,conventional ultraviolet absorption spectroscopy and theoretical calculations.The sample Li₂MoO₄ at ambient pressure and room temperature belongs to the trigonal system（R-3）,and a strong red fluorescence spectrum was observed under the excitation light of 355 nm（E～3.5 e V）.The ultraviolet absorption spectrum found that the band gap was E_g=4.33 e V.The density of states of Li₂MoO₄ was calculated using first principles,and it was found that the 4d orbital of Mo and 2p orbital of O provided electrons in the vicinity of the Fermi surface.Therefore,this fluorescence effect was derived from oxygen deficiencies.It is related to the radiation transition of the MoO₄ group near the oxygen vacancy.In the high-pressure Raman spectrum at room temperature,as the pressure increased,the Raman peak gradually broadened and showed red shifts.When the pressure reached 7 GPa,new Raman peak appears at 206 cm^-1 707 cm^-1,744 cm^-1.It might indicate pressure-induced structural phase transition.2)Li₂AMo₃O₈（A=In,Sc）were studied by conventional powder X-ray diffraction,ambient pressure and high-pressure Raman spectroscopy.The sample Li₂AMo₃O₈ （A=In,Sc）under ambient pressure and room temperature have a hexagonal structure（P6₃mc）.In the high-pressure Raman spectra at room temperature,as the pressure increased,the Raman peak gradually broadened and showed red shifts.In the High-pressure Raman spectroscopy of Li₂In Mo₃O₈,it was found that the Raman peaks at 124 cm^-1,197 cm^-1,205 cm^-1,252cm^-1 disappeared completely above 25.1GPa,and the relative peak intensity of the Raman modes peaks at 220 cm^-1,427 cm^-1 changed significantly.In the High-pressure Raman spectroscopy of Li₂Sc Mo₃O₈,it was found that the Raman peaks at 173 cm^-1,201 cm^-1,216 cm^-1,310 cm^-1,348 cm^-1,448 cm^-1disappeared completely above 26.7 GPa,and the intensity of the peak at 418 cm^-1gradually increased.The change could be related to the MoO₆ octahedral reorganization of in Mo₃O₁₃ clusters.It might also imply that a pressure-induced structural phase transition.3)Powder X-ray diffraction,ambient pressure and high-pressure Raman spectroscopy to study LiScMo₃O₈.The sample LiScMo₃O₈ at ambient pressure and room temperature has a different trigonal structure（P3m1）.High-pressure Raman spectroscopy were utilized at room temperature showed that the Raman peaks gradually broadened and exhibited red shifts with the increase of pressure,but no abnormal changes of the Raman peak shift and peak intensity could be observed up to 30 GPa.It showed that the crystal structure of the sample was stable in the studied pressure range.