(1. 南京航空航天大學(xué) 材料科學(xué)與技術(shù)學(xué)院，南京 210016；
2. 山東蒙沃變速器有限公司，臨沂 273300；
3. 上海交通大學(xué) 材料科學(xué)與工程學(xué)院，上海 200240)
摘 要: 采用基于密度泛函理論的第一性原理贗勢方法優(yōu)化Mg-Er合金體系中MgEr、Mg2Er和Mg24Er5這3種金屬間化合物的結(jié)構(gòu)模型，通過形成熱、結(jié)合能和電子結(jié)構(gòu)的計算分析了化合物的穩(wěn)定性與其晶體結(jié)構(gòu)的內(nèi)在聯(lián)系。結(jié)果表明：3種Mg-Er金屬間化合物的形成熱和結(jié)合能均為負值，化合物的形成能力和穩(wěn)定性均隨著化合物中Er含量的降低而降低。在費米能級低能級區(qū)域，Mg的3s、2p軌道與Er的4f、5d軌道發(fā)生重疊，產(chǎn)生了軌道雜化；在費米能級高能級區(qū)域，Mg的2p軌道與Er的5d軌道也存在少量的雜化。隨著化合物中Er含量的降低，化合物中平均每個原子在費米能級低能級處的成鍵電子數(shù)減少，化合物的穩(wěn)定性降低。在Mg、Er原子周圍均有大量的電荷存在，呈典型的金屬鍵特征，Mg、Er之間的電子云只有部分重疊，交界處電荷的畸變不大。Mg-Er金屬間化合物的價鍵結(jié)合具有金屬鍵和共價鍵兩重性，其中金屬鍵占主導(dǎo)地位。Mg、Er原子的電荷轉(zhuǎn)移量隨化合物中Er含量降低而減少，化合物的共價鍵性降低，穩(wěn)定性下降。
關(guān)鍵字: Mg-Er金屬間化合物；第一性原理；穩(wěn)定性；電子結(jié)構(gòu)
（1. School of Material Science and Technology, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China;
2. Shandong Menwo Transmission Co., Ltd., Linyi 273300, China;
3. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China）
Abstract:Using the first-principle pseudopotential plane wave (PPW) method based on the density functional theory, structural optimization was conducted on MgEr, Mg2Er and Mg24Er5 intermetallic compounds of the binary Mg-Er alloys, and the internal relations of the stability and crystal structure of the Mg-Er intermetallic compounds were analyzed by calculating the formation heat, binding energy and electronic structure. The results show that in Mg-Er alloys, the formation heat and binding energy of three intermetallic compounds are all negative, and the alloying ability and structural stability of Mg-Er compounds are in decline with decreasing the content of Er. In low-energy region of Fermi level, the energy band is mainly dominated by hybridization of 4f and 5d orbits of Er with the 2p and 3s orbits of Mg, while in high-energy region of the Fermi level, those bonds are mainly contributed by electrons of 5d orbits of Er and 2p orbits of Mg. As the Er content decreases, the average quantities of bonding electron of each atom in low-energy region of Fermi level drops, which results in the weakened interaction among valence electrons and the reduced stability. There are a large number of charges around Mg and Er, suggesting the characteristics of typical metal bond. Meanwhile, Mg and Er share some charges to form covalent bond, while the distortion of the charge at the junction is little. Therefore, the valence bond of Mg-Er intermetallic compound has a characteristic of the duality wherein the metal bond predominates. With decreasing the Er content, the amount of charge transfer between Mg and Er atoms reduces gradually, which leads to the decrement of the proportion of covalent bond and the structural stability.
Key words: Mg-Er intermetallic compounds; first-principle; structural stability; electronic structure
