Study On Preparation And Crystal Transition Thermodynamics Of Nano-VO₂?M? And V₂O₃ With Different Sizes And Morphplogies

The crystal transition thermodynamics of nanoparticles are different from that of bulk materials,since there are the differences in particle size and morphology of nanoparticles.The physical and chemical properties of VO₂?M?and V₂O₃ are greatly changed before and after the crystal transition,which are of great practical values.However,the effects of particle size and morphology on crystal trans ition temperature,crystal trans ition enthalpy and crystal transition entropy of nano-VO₂?M?and V₂O₃ are not clear.In this paper,we deduced the universal equations of crystal transition thermodynamics of nanoparticles by introducing the surface chemical potential into the classical thermodynamic theory.Furthermore,a core-shell model was proposed for the crystal transition thermodynamics of spherical nano-VO₂?M?,based on that we deduced the theoretical relations between particle size and crystal transition temperature,crystal transition enthalpy and crystal transition entropy of nano-VO₂?M?.Experimentally,the new ring-like VO₂?M?were successfully synthes ized for the first time by template-free hydrothermal method.The effects of N₂H₄·H₂O and hydrothermal filling rate on the morphology of ring-like VO₂?M?were also investigated.Moreover,the formation mechanism of ring-like structure proposed in this paper can provide a new way for research and synthesis of other ring-like nanomaterials.At the same time,the new single crystal flake-like V₂O₃ with hexagonal and half-hexagonal shape was successfully synthesized for the first time by one-step hydrothermal method,and the effects of N₂H₄·H₂O and aging temperature of sol-gel on its crystal type were investigated.For the first time,we use malic acid and NH₄VO₃ to synthesize the quasicube V₂O₃.In addition,through the control of different hydrothermal time,successful preparation of the average particle size range of20¹10 nm spherical VO₂?M?,and it was found that the oxidation temperature of spherical precursor of nano-VO₂?M?is the important factor of crystal shape.In the end,we also explored the effect of the crystallization transformation behavior of the carambola-like VO₂?M?and the influence of the doped Mo element on the transformation temperature and morphology of the nano-VO₂?M?crystal.The Results indicate that the particle size has an effect on the crystal transition thermodynamics of nano-VO₂?M?.That is to say:with the particle size of nano-VO₂?M?decreasing,the temperature,enthalpy and entropy of the crystal trans ition decrease,and these thermodynamic properties are all linearly related with the reciprocal of particle radius,which are consistent with the theoretical formulas.The experimental results can be used to predict and regulate the crystal transition behavior of nano-VO₂?M?with different particle sizes.In addition,different morphologies have an effect on the crystal transition behavior of VO₂?M?and V₂O₃.The ring-like VO₂?M?has much lower crystal transition temperature compared to that of the smaller spherical nanoparticles.The crystal trans ition temperature of the carambola-like VO₂?M?is also reduced compared with the bulk VO₂?M?.The crystal transition temperature of flake-like and pseudocube V₂O₃ are also lower than that of the corresponding bulk V₂O₃.