MnX (X=Ni, Pd and Pt)合金结构,声子谱,热力学性质的第一性原理研究
首发时间:2013-01-11
摘要:我们采用第一性原理方法对MnX(X = Ni,Pd和Pt)合金的结构,弹性,声子和热力学性质作了研究。研究了转变温度和能差对电子浓度的依赖关系。获得的相似的趋势表明因结构能差而引起的相稳定性趋势已得到了证实。对L10 晶格,计算的Mn与Mn之间的交换参数JMn-Mns随cv变化的函数显示主要的面间最近邻交换耦合J1L和面内次近邻交换耦合J2负责能差。计算结果表明顺磁B2结构的剪切模量(C'=C11-C12)为负值是导致立方结构向四方结构转变的原因。声子谱计算结果揭示了顺磁L10向反铁磁L10相变是由磁性引起的,而不是原子移动。此外还研究了其热力学性质,如德拜温度,各向异性及泊松比等,结果表明CuAu型反铁磁结构在低温时弹性稳定和动力学稳定,因此是低温结构。
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The structural, elastic, phonon, thermal and electronic properties of MnX (X=Ni, Pd and Pt) alloys: First-principles calculations
Abstract:We present first-principles studies of structural, elastic, phonon, thermal and electronic properties of MnX. Dependences of transformation temperatures and energy differences on concentration cv of valence electrons are investigated. Obtained similar trends indicate that predicted phase stability trends due to structural energy differences are confirmed. Calculated Mn-Mn exchange couplings JMn-Mns of L10 lattices as a function of cv reveal that dominating inter-layer nearest neighbors coupling J1L and in-plane next nearest neighbor coupling J2 are responsible for the energy differences. Obtained negative shear modulus (C′ = (C11-C12)/2) of paramagnetic B2 (PM-B2) triggers the cubic to tetragonal distortion. Calculated phonon dispersions indicate that paramagnetic L10 (PM-L10) to antiferromagnetic L10 (AFM-L10) transition is caused by magnetism rather than atomic moving. Debye temperature, anisotropy and Poisson's ratio are first assessed. Calculated results show that the CuAu-I type collinear antiferromagnetic structures are mechanically and dynamically stable in low temperatures, thus are the phases at low temperatures.
Keywords: First-principles calculations Transition metal alloys and compounds Elastic constants Electronic structure.
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MnX (X=Ni, Pd and Pt)合金结构,声子谱,热力学性质的第一性原理研究
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