(1. 東南大學(xué) 材料科學(xué)與工程學(xué)院，南京 211189；
2. 東南大學(xué) 江蘇省先進(jìn)金屬材料高技術(shù)研究重點(diǎn)實(shí)驗(yàn)室，南京 211189)
摘 要: 運(yùn)用基因遺傳算法的晶格結(jié)構(gòu)預(yù)測(cè)技術(shù)預(yù)測(cè)Pd基Heusler合金Pd2MnSn、Pd2CrGa和Pd2FeGa的結(jié)構(gòu)；采用基于密度泛函理論(DFT)的投影綴加波(PAW)方法研究Pd2CrGa和Pd2FeGa的四方變形、磁性、態(tài)密度、彈性常數(shù)和聲子譜線，最后通過(guò)Helmholtz自由能的計(jì)算預(yù)測(cè)了Pd2CrGa和Pd2FeGa的相變溫度。結(jié)構(gòu)預(yù)測(cè)顯示：極限條件0 K時(shí)，Pd2MnSn以L21立方結(jié)構(gòu)穩(wěn)定存在，而Pd2CrGa和Pd2FeGa均以四方結(jié)構(gòu)穩(wěn)定存在。四方變形中，Pd2CrGa、Pd2FeGa在c/a＜1.0和c/a＞1.0處均有一個(gè)能量的局域最小值，分別對(duì)應(yīng)一個(gè)穩(wěn)定的結(jié)構(gòu)。Pd2CrGa、Pd2FeGa在兩種狀態(tài)下均表現(xiàn)為鐵磁性，Cr原子和Fe原子是總磁矩的主要貢獻(xiàn)者。彈性常數(shù)計(jì)算結(jié)果顯示：Pd2CrGa和Pd2FeGa僅在四方結(jié)構(gòu)時(shí)才滿(mǎn)足穩(wěn)定性判據(jù)。c/a≈1.24處的四方結(jié)構(gòu)Pd2CrGa轉(zhuǎn)變?yōu)榱⒎浇Y(jié)構(gòu)的相變溫度在350 K左右，c/a≈1.30處的四方結(jié)構(gòu)Pd2FeGa轉(zhuǎn)變?yōu)榱⒎浇Y(jié)構(gòu)的相變溫度在130 K左右。
關(guān)鍵字: Heusler合金；結(jié)構(gòu)預(yù)測(cè)；四方變形；聲子
（1. School of Materials Science and Engineering, Southeast University, Nanjing 211189, China;
2. Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189, China）
Abstract:Based on genetic algorithm, the structures of Pd-based Heusler alloy Pd2MnSn, Pd2CrGa and Pd2FeGa were forecasted. The tetragonal distortion, magnetic, DOS elastic constants and phonon dispersion spectra of Pd2CrGa and Pd2FeGa were calculated by first-principles calculation based on DFT with projector augmented wave pseudopotential (PAW). At last, based on the result of Helmholtz free-energy, the phase transition temperatures of Pd2CrGa and Pd2FeGa were predicted. The crystal structure prediction shows that Pd2MnSn is L21 cubic structure, but Pd2CrGa and Pd2FeGa are tetragonal structures at 0 K. The tetragonal distortion analysis show that there are local minimums total energy at c/a＜1.0 and c/a＞1.0, which correspond to stable martensitic phases. Pd2MGa (M=Cr，F(xiàn)e) are ferromagnetic in these two postures, and M (M=Cr，F(xiàn)e) is the main magnetic contribution to its alloys, respectively. The elastic constants of Pd2CrGa, Pd2FeGa show that, cubic structure doesn’t satisfy stability conditions, but tetragonal structure satisfy the stability conditions at c/a≈1.24 and c/a≈1.30, respectively. Based on the results of Helmholtz free-energy, the phase transition temperatures of Pd2CrGa and Pd2FeGa tetragonal structure transferring to cubic structure are about 350 K and 130 K, respectively.
Key words: Heusler alloy; structure prediction; tetragonal distortion; phonon
