B2-RuAl点缺陷结构的第一原理计算

采用第一原理赝势平面波方法,计算了B2-RuAl金属间化合物的基本物性及其点缺陷结构的几何、能态与电子结构,通过对不同点缺陷结构形成热与形成能的计算与比较,分析和预测了RuAl金属间化合物中点缺陷结构的种类与存在形式.结果表明：RuAl金属间化合物的点缺陷主要是Ru空位和Al反位,在富Ru合金中主要为Ru反位,在富Al合金中则主要是Al反位.这些点缺陷主要以Ru-Ru双空位和Al-Al双反位的组态结构形式出现,并且双空位以Ru-Ru为第一近邻时其点缺陷结构最稳定,而双反位则是以Al-Al为第三近邻时稳定性最高.进一步通过对NiAl和RuAl不同点缺陷结构Cauchy压力的比较,发现点缺陷对RuAl塑性的降低程度比NiAl低,因而含有点缺陷的实际合金的室温塑性RuAl比NiAl好.

First-Principle Calculation of Point Defective Structures of B2-RuAl Intermetallic Compound

Using a first-principle pseudopotential plane-wave method, the energetic, geometrical and electronic structures of point defects are calculated for B2-RuAl intermetallic compound. Based on the calculation and comparison of the formation heat and formation energy for several kinds of point defective structures, the type and the geometrical configuration of point defects in B2-RuAl intermetallic compound are analyzed and forecasted. Results show that the major point defects in B2-RuAl intermetallic compound are vacancy or anti-site in the Ru sublattice, i.e., Ru vacancy and Al anti-site, but mainly Ru anti-site defect in rich-Ru alloy, and mostly Al anti-site defect in rich-Al alloy. These point defects emerge in the form of Ru-Ru double vacancy or Al-Al double anti-site configurations, namely, there are two vacancies or two Al atoms in the Ru sublattice. And they would be in the most stable structure when the double vacancies at Ru sites were in the first nearest neighborhood, or when the double Al atoms at Ru sites were in the third nearest neighborhood. In addition, the influences of above point defects on Cauchy pressre parameter(C12-C44)of B2-RuAl and NiAl were also compared. It is found that the decreasing of C12-C44 caused by point defects in RuAl is smaller than that in NiAl, so that the ductility of RuAl metallic compound with point defects at room temperature is better than NiAl.