【作者】 刘妍；

【导师】 李达；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2020， 硕士

【摘要】 对材料施加应变可以使其发生结构变化,是材料科学中设计新颖材料的一种有力手段。材料费米能级附近的电子态与其晶体结构中相邻原子的电子轨道相互作用密切相关,在应变场的作用下,电子轨道重组,导致材料电子性质发生改变。调整外加应变的大小、方向,可以实现在不引入杂质的前提下,显著改变材料的电子结构及成键模式,达到调控材料性能的目的。前人研究表明应变工程是调控材料性质的一种有效且绿色的手段,有着巨大的应用前景。随着现代计算机技术的飞快发展及理论方法的不断改进,利用密度泛函理论的第一性原理计算能够模拟材料在施加应变过程中的变化,进而探究在外加应变场下材料物理化学性质的改变,为设计新材料提供有力的数据支撑。方钴矿是化学式为AB3(A为Ir、Co、Rh等,B为As、P、Sb等)的二元磷族化合物,拥有良好的热电性能且环境友好,是目前备受瞩目的热电材料。研究表明金属掺杂是调控方钴矿性能的一种方式,前人观察到Ba掺杂使得磷族方钴矿结构IrAs3和IrP3(Ba)(Ir4X12)经历了非金属到金属的转变。但是精确控制掺杂原子的位置和数量具有很高的挑战,而且极易引进杂质,实验过程存在诸多阻碍。鉴于前期对应变工程的调研,我们猜测施加应变或许可以作为实现这类材料金属化的另一种有效手段。因此,本文采用第一性原理的计算方法,选取方钴矿中具有代表性的IrAs3作为研究对象,探究应变诱导的结构转变,以及在转变过程中晶体结构、电子结构和成键方式的变化规律,获得以下研究成果:1、在应变作用下IrAs3的带隙逐渐减小,直至最终闭合。在<100>方向施加拉伸应变时,带隙变化最为敏感,约9%的单轴拉伸应变就可以实现IrAs3的半导体-金属转变。在反向压缩应变的作用下,带隙完全复原,说明该半导体-金属转变具有可逆性。2、应变诱导的八面体姜-泰勒效应和砷四元环断裂是导致IrAs3半导体-金属转变的根本原因。另外,IrAs3中具有较强电负性的铱原子在八面体场及应变场的作用下成为电子受体,接收来自砷四元环的价电子。3、静水压同样会诱导IrAs3带隙闭合。但应变工程在IrAs3的半导体-金属转变中比静水压更有优势。该研究成果不但可以帮助理解应变对于方钴矿材料结构与性能的调控作用,还建立一种有效且经济的应变诱导金属化方法,为运用应变工程设计性能优异的方钴矿材料提供一种新的视角。更多还原

【Abstract】 Applying strain to materials can cause structural changes,which is a powerful method for designing novel materials in materials science research.The electronic state near the Fermi energy level of the material is closely related to the electronic orbital interaction of adjacent atoms in the crystal structure.The electron orbits reorganize under the action of the strain field,which causes the electronic properties of the material to change.Previous studies have shown that strain engineering is an effective and green method to regulate the properties of materials and has a great application prospect.With the rapid development of computer technology and the improvement of theoretical methods,the first-principles calculation methods based on density functional theory can simulate the changes of materials in the process of applying strain,and then explore the changes of the physical and chemical properties of materials under the applied strain field,providing powerful data support for the design of new materialsAs a kind of binary phosphorous compound with the chemical formula AB3(A=Ir,Co,Rh,etc.,B=As,P,Sb,etc.),skutterudite is the promising thermoelectric materials with excellent thermoelectric properties and is environmentally friendly.Previous studies have shown that metal doping is a good way to regulate the properties of skutterudite.Very recently,the Ba doping makes iridium pnictides IrAs3 and IrP3(BaxIr4X12)undergo a nonmetal-to-metal transition.However,the precise control of the position and the number of doped atoms are very challenging,and it is very easy to introduce impurities,and there are many obstacles in the experimental process.In view of the previous investigation of strain engineering,we speculate thatapplying strain may be another methods to achieve the metallization of these materials.In this paper,we mainly adopted the first-principles calculation method,selected skutterudite material IrAs3 as a representative,explored the strain-induced structural transformation,as well as the changes in crystal structure,electronic structure,and bonding mode during the transformation process.The following research results are obtained:1.The band gap of IrAs3 decreases gradually under the strain until it is completely closed.When the tensile strain is applied along the<100>direction,the change of band gap is the most sensitive.About 9%of uniaxial tensile strain can achieve the semiconductor-metal transition of IrAs3.Under the action of reverse compressive strain,the band gap is completely restored,indicating that the semiconductor-metal transition is reversible.2.The strain-induced octahedral Jahn-Teller effect and the fracture of the As4-rings are the fundamental causes of semiconductor-metal transition.In addition,the iridium atom with strong electronegativity in IrAs3 becomes electron acceptor under the effect of the octahedral field and strain field,and receives valence electrons from the As4-rings.3.Hydrostatic pressure can also induce the closure of band gap in IrAs3.However,strain engineering has more advantages over hydrostatic pressure in the semiconductor-metal transition of IrAs3.These research results will not only help understand the regulating effect of the strain on the structure and properties of skutterudite materials,but also establish an effective and economical method of strain-induced metallization,providing a new perspective for using strain engineering to design skutterudite materials with excellent performance.更多还原