IrTi合金晶格动力学的第一性原理研究

利用密度泛函理论的平面波赝势方法研究了IrTi合金的晶格动力学行为. 声子谱计算表明四方(L1₀)结构动力学不稳定,通过冷冻不稳定声子模式, 发现IrTi会发生从四方(L1₀)到正交的结构相变.进一步分析软模对应的原子振动, 得到了具有正交对称性,空间群为Cmmm,相对于四方(L1₀)相能量更低、更稳定的结构. 这种正交新相(Cmmm)弹性稳定和动力学稳定,而且其结构参数与实验上观察到的低温结构有限的晶格参数相符合,表明IrTi合金的低温相是正交结构(Cmmm). 从理论上肯定了IrTi合金立方到四方再到正交的相变机制, 解决了实验上关于相变机制和低温相结构形式的争议.

First-principles study of lattice dynamic of IrTi alloy

The structural behaviors of IrTi are studied using first-principles density-functional theory with pseudopotentials and a plane-wave basis.Phonon calculations indicate that the tetragonal(Llo) structure is dynamically unstable.We obtain the orthorhombic structure (Cmmm) which is shown to be a global energy minimum by the frozen phonon method.The resulting structure is mechanically and dynamically stable and its lattice constant is similar to the experimentally observed lattice constant of low-temperature structure,which demonstrates that the low-temperature phase of IrTi is the orthorhombic structure(Cmmm).Thus,we put an end to the experimental debate regarding the low-temperature phase:whether it is orthorhombic or monoclinic,and demonstrate theoretically that the IrTi alloys will undergo a cubic→tetragonal→orthorhombic transformation.