Preparation And Thermal Expansion Properties Of The AlMoVO₇ And (CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄

With the continuous development of industrial technology,the requirements for material performance are getting higher and higher.For example,aerospace equipment,precision measuring instruments and optical devices require extremely high accuracy and precision.However,materials generally have thermal expansion and contraction properties.When the ambient temperature changes,the length or volume of its parts will change,which seriously affects its accuracy and precision.The use of zero or near-zero expansion materials is a very effective means to solve the above problems,but natural zero-expansion materials are very rare.Therefore,the discovery and preparation of near-zero expansion materials with excellent performance have important application value.The first part of this article is to discover and prepare a new near-zero expansion material Al Mo VO₇.Using negative expansion materials to combine with common materials is an effective way to prepare zero or near-zero expansion materials,and the discovery and preparation of negative expansion materials with excellent performance are the basis for the application of this technology.In recent years,high-entropy materials have received much more attention because of a"cocktail"effect,that means multi-component synergistic effect,presenting special properties and have broad application prospects in the fields of energy,aerospace and environment.Trying to prepare this material is a useful attempt.The second part of this article is to design and prepare negative expansion material(CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄with high-entropy.The main content and results of the paper are as follows:1.Preparation,thermal expansion and mechanism research of Al Mo VO₇,a near-zero expansion material.A new near-zero expansion material of Al Mo VO₇ was prepared by the solid-phase method,showing near-zero expansion in a wide temperature range of 173-673 K,with an expansion coefficient of 0.58×10^-6 K^-1,it's not absorbent and it has good thermal stability and great application potential.Al Mo VO₇ has an orthogonal structure,[Al O6]octahedron is connected to[Mo O₄]tetrahedron through a common apical oxygen atom and linked with[VO₅]square pyramid co-edge to form the framework structure of Al Mo VO₇.The expansion mechanism:With increases temperature,the librational and translational vibrations between[Mo O₄]and[Al O₆]lead to the bending of the Al-O-Mo chain.The decrease of the nonbonding Al···Al distance leads to the decrease of the a.The increase of the nonbonding Al···Mo and V···V distance leads to the increase of the b and c,and Al Mo VO₇unit cell expansion has anisotropic and near-zero thermal expansion.The thermal expansion performance of Al Mo VO₇ block depends on its unit cell structure and microstructure.Therefore,it exhibits near-zero expansion in the temperature range of 173-673 K.2.Preparation of high-entropy oxide(CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄ and exploration of its negative thermal expansion performance.(CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄ was prepared by solid phase method and XRD test showed that it was a single hexagonal phase.In the temperature range of 173-673 K,there is no phase change,no water absorption,and good thermal stability.SEM and EDS test showed that the sample is composed of randomly distributed irregular particles and many pores,so it has low compactness.All elements are uniformly distributed in the sample,and there is no element aggregation.(CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄ exhibits negative thermal expansion characteristics,and the expansion coefficient?=-2.40×10^-6 K^-1.The translation and libration between[PO₄]tetrahedron and[Zr O₆]octahedron,coupled with the influence of the microstructure,finally made the(CaMgSrNa₂K₂)_0.2Zr₄P₆O₂₄ sample exhibit negative thermal expansion characteristics at 173-673 K.