First-principles Studies On The Structures And Electronic Properties Of Be_xZn_1-xO Ternary Alloys Under High Pressure

Zinc oxide(ZnO),a kind of functional device material,has attracted much attention,due to its excellent characteristics and great significance in the fields of optics,electricity,photoelectricity,piezoelectricity,magnetism,and photocatalysis.ZnO is a II-VI oxide semiconductor with a wide bandgap,large exciton binding energy,low dielectric constant,large photoelectric coupling rate,and strong structural stability.Therefore,ZnO represents an attractive prospect with great potential for use in many fields.Be O and ZnO share the same hexagonal symmetry,and Be O is considered to be one of the best alternative materials for achieving wide bandgap modulation.In recent years,several studies have been conducted in relation to these compounds,but systematic studies on different composition ratio are still lacking.In our work,we analyze the ternary alloys Be_xZn_1-xO under high pressure by using first-principles calculations,with the aim of providing a comprehensive theoretical underpinning for future studies.In this paper,the Universal Structure Predictor:Evolutionary Xtallography crystal structure prediction software package used to conduct a systematic structural search for ternary alloys Be_xZn_1-xO in a pressure range from 0-60 GPa.After that,we used the first-principles calculation that is based on the density functional theory to study the stability and electronic characteristics of Be_xZn_1-xO with different components.The calculated results show that ternary alloys Be_xZn_1-xO are metastable at pressures ranging from 0 to 60 GPa.These structures include BeZn₄O₅(P2₁,Pmn2₁),BeZn₃O₄(Pmn2₁-a,Pmn2₁-b),BeZn₂O₃(Cmc2₁,Pmma),BeZnO₂(Pna2₁,Pca2₁),Be₂ZnO₃(Cmc2₁),Be₃ZnO₄(Pmn2₁,C2),Be₅ZnO₆(P31m),and Be₂Zn₃O₅(Cmc2₁).Further studies show that the Be₂ZnO₃,Be₅ZnO₆,and Be₂Zn₃O₅are stable in the Cmc2₁,P31m,and Cmc2₁structures,respectively,at pressures ranging from 0 to 60 GPa,and no phase transition occurs.While for BeZn₄O₅,BeZn₃O₄,BeZn₂O₃,BeZnO₂,and Be₃ZnO₄,each of them has two structures.From 0 to 16 GPa,BeZn₄O₅is stable in the P2₁structure,then transforms into a Pmn2₁structure.For BeZn₃O₄,the two Pmn2₁structures(referred to as Pmn2₁-a and Pmn2₁-b)are found to be most stable over pressure ranges of 0-26,and 26-60 GPa,respectively.BeZn₂O₃is stable in Cmc2₁symmetry at zero pressure,transforming into a Pmma structure at 34 GPa.For BeZnO₂,Pna2₁and Pca2₁structures are found to be most stable in the pressure ranges of 0-29,and 29-60 GPa,respectively.The Pmn2₁to C2 Be₃ZnO₄transformation occurs at 46 GPa.Then we studied the electronic properties of these crystal structures.The calculated results show that the bandgap of the ternary alloys Be_xZn_1-xO increases with an increase in Be content at the same pressure.Moreover,the bandgap of the ternary alloys Be_xZn_1-xO increases with increasing pressure with fixed Be content.