Wu Mengxin, Zhou Feng, Khenata Rabah, Kuang Minquan, Wang Xiaotian
School of Physical Science and Technology, Southwest University, Chongqing, China.
Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Université de Mascara, Mascara, Algeria.
Front Chem. 2020 Dec 11;8:546947. doi: 10.3389/fchem.2020.546947. eCollection 2020.
In this work, we investigated the phase transition and electronic structures of some newly designed all--metal Heusler compounds, XMnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L2 structures of these materials was studied, and we found that XMnTi favors to feature the L2-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L2 structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L2 structure is no longer the most stable structure, and a more stable tetragonal L1 structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L2 to tetragonal L1 structure). This mechanism of L2-L1 structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L1 and L2, defined as Δ (Δ = - ), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal XMnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L1 state. We hope that our research can provide a theoretical guidance for future experimental investigations.
在这项工作中，我们通过第一性原理研究了一些新设计的全金属赫斯勒化合物XMnTi（X = Pd、Pt、Ag、Au、Cu和Ni）的相变和电子结构。研究了这些材料中XA和L2结构之间的竞争，我们发现XMnTi倾向于具有L2型结构，这与著名的位点偏好规则（SPR）一致。在L2结构下，我们研究了这些材料最稳定的磁态，发现铁磁态由于能量较低而最稳定。通过四方变形，我们发现L2结构不再是最稳定的结构，出现了更稳定的四方L1结构。也就是说，在四方应变下，材料发生四方相变（即从立方L2结构转变为四方L1结构）。基于计算得到的态密度，详细讨论了L2-L1结构转变的机制。此外，我们发现L1和L2最稳定相之间的能量差，定义为Δ（Δ = - ），可以通过均匀应变来调节。最后，展示了所有四方XMnTi（X = Pd、Pt、Ag、Au、Cu和Ni）相的声子谱，这为四方L1态的稳定性提供了有力证据。我们希望我们的研究能够为未来的实验研究提供理论指导。
