Al_3M(M=Ti,Zr,Hf)亚稳相和平衡相的价电子结构分析

VALENCE ELECTRON STRUCTURE ANALYSIS OF EQUILIBRIUM AND METASTABLE PHASES OF Al_3M(M=Ti,Zr,Hf)

本文运用固体与分子经验电子理论(EET)计算了Al_3M(M=Ti,Zr,Hf)的3种晶体结构(L1_2,D0_(22),D0_(23))的价电子结构和最强键键能,并依此对各种结构的相稳定性及相变顺序做半定量分析.结果显示:各平衡相,即D0_(22)-A1_3Ti,D0_(23)-Al_3Zr和D0_(22)-Al_3Hf,其最强键键能分别为57.7,71.6和75.6 kJ/mol,与对应平衡相的熔点高低次序一致,确认了EET计算结果的可靠性.使用这一方法计算获得Al_3Ti,Al_3Zr和Al_3Hf的最强键键能,依此得出各亚稳相向平衡相的转变顺序与实验结果及第一性原理计算的结果相同.EET计算的最强键键能可作为评价亚稳相稳定性的一个判据.据此,由计算获得L1_2型Al_3M最强键键能推论各相的稳定性次序为Al_3Ti<Al_3 Zr<Al_3Hf,与实验所得的相稳定性次序一致,表明最强键键能作为亚稳相稳定性判据的正确性.

The valence electron structure of A1_3M（M=Ti,Zr,Hf） with three crystal structures （L1_2,D0_（22）,D0_（23）） and tne corresponding strongest bond energy（？＂.4） values have been calculated from the empirical electron theory（EET） of solids and molecules.Based on the calculated E_a,the stability of the phases with different structures and the sequence of phase transition have been analyzed semi-quantitatively.The results showed that,the E_a of the equilibrium phases,i.e.,DO22 A1_3Ti, D0_（23）-Al_3Zr and D0_（22）-A1_3Hf,were 57.7,71.6 and 75.6 kJ/mol,respectively,which showed the same trend in magnitude with the corresponding melting point.This consistence supports the reliability of EET-based calculation results.Similarly,the E_a of A1_3Ti,A1_3Zr and A1_3Hf with three structures have been calculated and the calculated phase transition sequences are the same as the experimental results and those from first-principles calculation.The L1_2-type metastable phases of three intermetallic compounds exhibit many excellent characteristics,whereas their phase stability is crucial for application.The E_a is supposed to be a measure for the stability of metastable phase.The calculated E_a of L1_2 structure implied the phase stability in the order of A1_3TiA1_3ZrAl3Hf.which was the same as that from the transition temperatures experimentally.The E_a calculated by EET.therefore, could be a good measure for the stability of metastable phase.