Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm, SE-10044, Sweden.
Department of Materials and Nano Physics, School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, SE-16440, Kista, Sweden.
Sci Rep. 2017 Jun 19;7(1):3778. doi: 10.1038/s41598-017-03877-5.
Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at ~700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion. Our analysis of the energy of the phases shows that magnetic effects alone cannot drive the fcc-hcp transition in Co and that the largest contribution to the stabilization of the fcc phase comes from the vibration of the ionic lattice. By including all the contributions to the free energy considered here we obtain a theoretical transition temperature of 825 K.
确定驱动相变的力一直是具有挑战性的。在 ~700K 发生在钴中的 hcp-fcc 相变尚未被完全理解，尽管早期的理论研究表明，在高温下，磁性在 fcc 相的稳定中起着主要作用。在这里，我们对这两个相的自由能进行了第一性原理研究，我们将它们分解为晶格振动、电子和磁系统以及体积膨胀引起的贡献。我们对相的能量的分析表明，仅仅是磁性效应不能驱动 Co 中的 fcc-hcp 转变，对 fcc 相稳定的最大贡献来自于离子晶格的振动。通过包括这里考虑的自由能的所有贡献，我们得到了一个理论转变温度为 825K。
