Theroretical Design And Physical Properties Of Typical Rare Earth Metal Nitrogen-rich Compounds Under High Pressure

With the progress of The Times at full speed,people are in the face of the increasingly prominent problem of environmental pollution.In the production of traditional energy-containing materials,most of the high-energy compounds will cause serious environmental pollution when they are synthesized.Therefore,it is urgent to find environmentally friendly high energy density materials(HEDMs).Metal nitrogen-rich compounds are not only characterized by high energy,but also have good stability and will not increase the burden of the environment during production.They are new materials with high energy density.Based on particle swarm optimization algorithm is adopted in this thesis a new crystal structure prediction program,CALYPSO method,and combined with the first principles calculation,to predict the system YN_x(x=1/4?2/7?1/3?2/5?1/2?1?3/2?2?5/2 and(3-12)of different chemical units in some low enthalpy under high pressure of the structures,through the comparison in 0,25,50,75 and 100 GPa pressure relative to disintegrate into solid Y and N₂formation enthalpy to find out the structure of a relatively stable proportion:Y₅N₂,Y₃N₂,YN,YN₂,YN₃,YN₄,YN₅,YN₈and YN₁₀.The structure,electronic structure characteristics and mechanical properties of these stable ratios are discussed in detail,which will be of great significance to the follow-up experiments.Here are some innovative results.In this paper,we adopt effective crystal structure search method(CALYPSO)from 0 to 100 GPa pressure range to a wide range of yttrium nitride structure search,and connecting with the first principle computing research the different ratio of yttrium nitrogen compounds(Y₅N₂,Y₃N₂,YN,YN₂,YN₃,YN₄,YN₅,YN₈and YN₁₀)structure,mechanical properties and electrical properties,study found that many high nitrogen content of yttrium nitrogen compounds can form under the pressure of relatively mild.Our results show that nitrogen can react with yttrium at relatively low pressure(about 10 GPa)to form energy-dense compounds with a variety of components.Their structures are diverse,including one-dimensional polymer crystals(e.g.,YN₄/YN₅)and three-dimensional infinitely extending stereograms(e.g.,YN₈).In the calculation,it is found that the nitrogen-rich YN₅and YN₈compounds can be recovered as metastable high-energy materials under environmental conditions,and can release a large amount of energy when decomposed into molecular nitrogen and YN(2.51k Jg^-1and 3.18k Jg^-1).The most surprising thing is that YN₈,a three-dimensional structure,shows a surprisingly high energy density and is the most energy-dense nitrite among all known polynitrogen compounds,making YN₈a promising candidate for HEDMs.Our discovery enriches the species of nitrogen-rich metallic compounds and opens the way for the design and synthesis of novel materials with high energy density.