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采用第一性原理平面波赝势方法研究了合金元素X(X=Ca、Sr、Ba)掺杂Mg2Si的占位情况:(1)取代Mg原子位置;(2)取代Si原子位置;(3)间隙固溶到Mg2Si晶胞中。分析合金系Mg7Si4X,Mg8Si3X,Mg8Si4X的形成热和结合能可知,Mg7Si4X的形成热和结合能均为负值,且最小。表明Mg7Si4X更容易形成稳定化合物,具有较强的合金化能力,且Ca,Sr,Ba掺杂Mg2Si时有优先占据Mg原子的倾向。研究Mg7Si4X的弹性模量和电子结构发现:Mg7Si4Ca、Mg7Si4Sr为脆性相;Mg7Si4Ba为延性相,塑性最好;掺杂Ca,Sr,Ba使Mg2Si逐渐由脆性向韧性转变。Ca,Sr,Ba的掺入均使Mg2Si的电子态密度发生偏移,费米能级处的电荷密度增加,导电性增强,共价键作用减弱,合金系结构稳定性减弱。
The first-principle plane-wave pseudopotential method was used to study the occupancy of Mg2Si doped with alloying elements X (X = Ca, Sr, Ba): (1) substitution of Mg atom; (2) substitution of Si atoms; (3) Gap solid solution into Mg2Si unit. Analysis of the formation of Mg7Si4X, Mg8Si3X and Mg8Si4X alloy shows that the heat of formation and the binding energy of Mg7Si4X are both negative and minimum. It shows that Mg7Si4X is easier to form a stable compound with stronger alloying ability, and Ca, Sr and Ba preferentially occupy Mg atoms when doped with Mg2Si. Study on the elastic modulus and electronic structure of Mg7Si4X found that: Mg7Si4Ca, Mg7Si4Sr brittle phase; Mg7Si4Ba ductile phase, plasticity best; doping Ca, Sr, Ba Mg2Si gradually transition from brittleness to toughness. The incorporation of Ca, Sr and Ba both shifted the electronic density of state of Mg2Si, the charge density at Fermi level increased, the conductivity increased, the covalent bonding effect weakened, and the stability of the alloy system decreased.