Y掺杂SrAl2Si2的电子结构与光学性质的第一性原理研究

2020-05-18 02:41刘娟陈中钧赖仓隆
科技创新与应用 2020年14期
关键词:结构

刘娟 陈中钧 赖仓隆

摘  要:文章采用基于密度泛函理论的第一性原理方法研究掺杂Y的Sr1-xYxAl2Si2(x=0,0.25,0.5和0.75)的晶体结构、电子性质和光学性质。研究发现掺杂Y的SrAl2Si2晶体结构发生了明显的压缩,Sr0.5Y0.5Al2Si2发生了相变,由三方晶系转变为单斜晶系。此外,能带结构的计算表明,SrAl2Si2是一种半金属,在导带和价带之间有很小的重叠。掺杂Y原子后,SrAl2Si2从半金属向金属转变,并且随着掺杂浓度从x=0.25,0.5到0.75,其金属性逐渐增强,这与态密度(DOS)的计算结果一致。这些结果表明,通过提高Y的掺杂浓度,SrAl2Si2基合金的热电性能很可能得到进一步的改善。最后,计算并分析了掺杂Y的Sr1-xYxAl2Si2(x=0,0.25,0.5和0.75)晶体的介电函数、能量损失谱和反射谱,得出Sr1-xYxAl2Si2是一种前景较好的介电材料,并且在20-30 eV能量范围内是良好的紫外透光材料。

关键词:第一性原理计算;Sr1-xYxAl2Si2;结构;电子性质;光学性质

中图分类号:O469          文献标志码:A         文章编号:2095-2945(2020)14-0001-07

Abstract: The First-Principles methods are used to study the structural, electronic and optical properties of the Y-doped Sr1-xYxAl2Si2(x=0, 0.25, 0.5 and 0.75). Indeed, the structure was compressed evidently for Y-doped SrAl2Si2, and a structural transition was observed from trigonal to monoclinic configuration for Sr0.5Y0.5Al2Si2. Besides, the structure calculations revealed that SrAl2Si2 undergo semimetal to metal-like transition and the metallic characteristics was enhanced with increasing Y content from x=0.25, 0.5 to 0.75, which is consistent with the density of states (DOS). Finally, the dielectric function, absorption spectrum, energy-loss spectrum and reflectivity were calculated and analyzed for Y-doped SrAl2Si2 crystals, which shows that it is a promising dielectric material and UV-transparent material around the range (20-30 eV).

Keywords: First-Principles calculation; Sr1-xYxAl2Si2; structure; electronic properties; optical properties

1 概述

以過渡金属或碱性稀土金属为主要组成部分的硅化物,由于具备多种优良的物理特性而受到了广泛关注。[1-2]近年来,有研究表明态密度在费米能级处存在赝能隙的半导体(或半金属)化合物,通常具有特殊的电子性质,具备成为性能优良的热电材料的潜力,[3]这使得该类材料成为研究热点。Kauzlarich等人[4]通过实验证明,SrAl2Si2态密度的费米能级处存在赝能隙,这使其有望成为优良的候选热电材料;然而纯SrAl2Si2的热电性能并不理想,这是因为在室温下它的电阻率(ρ≈8mΩ cm)和热导率(k≈4W/mK)都较大。如何降低电阻率和导热率以获得良好的热电性能是研究人员面临的两个主要挑战。早先,Lue等人[5]在实验和理论计算中将Y掺杂到SrAl2Si2中Sr的位置,发现Sr1-xYxAl2Si2(0≤x≤0.2)的电阻率显著减小,并指出这与掺杂修正了SrAl2Si2的电子能带结构有关。但是,到目前为止还没有关于更高浓度的Y掺杂SrAl2Si2的电子性质和光学性质的理论研究。所以,本文计算并分析了Sr1-xYxAl2Si2(x=0,0.25,0.5和0.75)材料的结构、电子和光学性质。

4 结论

本文采用DFT-GGA的计算方法研究了Sr1-xYxAl2Si2 (x=0,0.25,0.5和0.75) 的晶体结构、电子性质和光学性质。Y原子的掺入使得SrAl2Si2晶体结构被压缩,并且当掺杂浓度x=0.5时,晶体结构从三角结构转变为单斜结构。能带结构和态密度的计算结果表明,本征SrAl2Si2属于半金属材料,掺杂Y原子后转变为金属,并且随着掺杂浓度的增大体系费米能级处的态密度逐渐增大、费米能级上移,这使得其金属性不断增强。这一研究结果为提高SrAl2Si2材料的热电优值提供了一个新思路,使该材料体系成为更具吸引力的候选热电材料。最后,通过对比分析几种不同掺杂浓度的介电函数、吸收光谱、反射谱、能量损失谱,得出掺杂Y后的SrAl2Si2材料不仅是前景很好的介电材料,在20~30eV能量范围内还是一种好的紫外透光材料。

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