Study On The Preparation Etching Characterization And Electronic Properties Of ?MoY?₂AlC MAX Phase

The Mo-based MAX phase and MXene have many excellent properties.Until now,the bulk sintering and chemical etching of the (Mo_2/3Y_1/3)₂AlC MAX phase have not been studied.In this paper,Spark Plasma Sintering and the elemental powder are used to synthesis?MoY?₂AlC MAX phase,at different temperature and with different Mo:Y ratio.The MAX phase and corresponding product were analyzed by a series of material characterization techniques to determine the phase composition,microstructure,crystal etc.The MAX phase was etched using different chemical etchants such as HF,TMAOH and LiF+HCl.The first-principles density functional theory method was used to study the electronic properties and mechanical properties of MAX phase and MXene.The results show that when the Mo:Y ratio is 2:1 the whole system is the most stable at the same time (Mo_2/3Y_1/3)₂AlC MAX phase is obtained,and the sintering temperature is suitable at 1550°C.Accordion-like MXene was not observed by using 40 wt%HF,but a strip-shaped two-dimensional sheet appeared which's Mo:Y was approximately equal to1:1.When 50 wt%HF is used there was no significant two-dimensional sheet was observed.TMAOH did not react with the MAX phase,in the range of 25-45°C.By changing the molar ratio,LiF and MAX phases,the reaction time accordion-like MXene Mo_1.33CT_x,with functional groups on the surface,was observed which etched both Y and Al.The wrinkle curl was observed by transmission electron microscopy,indicating that the material is flexible.The results of first-principles calculations show that the MAX phase exhibits metal property through calculation the energy band and the density of states.MAX phase's Young's modulus is 226.886 GPa,bulk modulus is 153.409 GPa,shear modulus is 90.500GPa,the Poisson's ratio is 0.254,and the B/G is 1.695 which is less than 1.75 show a brittle material.Through the calculation of MXene and the comparison with Mo₂C,it is found that the position of the surface functional group of Mo_1.33C is consistent with Mo₂C,which is located directly above the non-adjacent Mo atoms.The calculation of energy band and density of states shown that when the surface functional group is F,Mo₂C exhibits a semiconductor property with the band gap of 0.39 eV,but Mo_1.33C exhibits the metal property.When the surface functional group is O and OH,both of them exhibit the metal property.But when the surface functional group is a mixture of O and F,the ratio is2:1,Mo_1.33C exhibits the semiconductor property with the band gap of 0.4 eV,while Mo₂C exhibits the metal property.It was found that all of Mo_1.33CT₂'s elastic constant C₁₁1 is less than Mo₂CT₂,when the surface was O,F,OH and a mixed functional group.