Study On The Synthesis And High Pressure Phase Transitions Of Micro-nano Structure Vanadium Oxides

Vanadium oxide possesses a unique structure and exhibits excellent physical and chemical properties.It is widely used in the fields of lithium ion batteries?LIB?,supercapacitors,catalysts,optoelectronics,electrical equipment,energy-saving smart windows,ultrafast optical switches,and electroacoustic equipment.Studying the relationship between its structure and physical properties has an important scientific significance for further enriching the understanding of vanadium oxide and expanding its application.High pressure is an effective tool to regulate the structure and properties of materials and explore their relationship.Pressure cannot only effectively shorten the distance between atoms,induce structural phase transitions,and form high-pressure new phases,but also help us explore new structures,new properties,and new phenomena of matter under high pressure.At present,the law of V₂O₃structural phase transition under high pressure is not clear,and the influence of morphology and size on the phase transition of high-voltage structure and electrical transmission characteristics is lacking.Therefore,the high-pressure study of micro-nano structure vanadium oxide will further enrich our understanding of the system.In this paper,a variety of vanadium oxide?V₂O₃,V₂O₅,VO₂?micro-nano spheres with regular morphology were synthesized by hydrothermal method,and further studied by high-pressure in-situ synchrotron radiation X-ray diffraction?XRD?,electrical measurement and other experimental methods V₂O₃ micro-nano sphere structure phase transition and electrical transport characteristics under high pressure.The research results of this paper are as follows:1.The precursor vanadium glycolate?VEG?was synthesized by hydrothermal method,and then calcined at different temperatures,different heating rates,and different atmospheres to prepare a porous structure of vanadium oxide?V₂O₅,VO₂,V₂O₃?microspheres.2.Through the control variable method,we explored the factors that affect the diameter of the microspheres.It was found that during the hydrothermal synthesis process,the spherical diameter of the precursor vanadium glycolate?VEG?will follow the hydroxylamine hydrochloride within a certain range.The stirring time of the mixed solution with ammonium metavanadate increases and the size of the spherical diameter can be adjusted within the range of 3-15?m.3.Using high-pressure synchrotron radiation XRD technology,the phase transition of corundum phase V₂O₃ micro-nano spheres was studied.It was found that the corundum phase transformed into a high-pressure monoclinic phase at 34.7 GPa under high pressure.The bulk elastic modulus of corundum-phase V₂O₃micro-nanospheres is obviously improved compared with corresponding bulk materials and polycrystalline materials,but it is close to that of corresponding nanoparticles.This may be due to the size effect and higher crystallinity,resulting in V₂O₃ micro-nano spheres with larger bulk modulus.4.The high-pressure resistance measurement method was used to study the electrical transport characteristics of V₂O₃ micro-nano spheres,revealing the relationship between their electrical characteristics and crystal structure.Studies have shown that the metallicity of V₂O₃ microspheres is enhanced under the effect of pressure,but when the corundum phase is transformed into a high-pressure monoclinic phase,the resistance shows an increasing trend,which may be due to the lattice distortion caused by the change of the crystal structure when the structure phase changes,Thereby suppressing charge fluctuations.During the pressure relief process,it was found that the V₂O₃ micro-nano spheres recovered from the high-pressure monoclinic phase to the original corundum phase.The phase change of V₂O₃ micro-nano spheres under high pressure is a reversible process.At the same time,the resistance of the V₂O₃ micro-nano spheres increases with decreasing pressure,which is consistent with the changing law of the boosting process.This shows that its power transmission operation is also very reversible.