MgO高温高压特性及相变的第一性原理研究

应用第一性原理密度泛函理论计算了MgO在零温(0K)下和0~200GPa静水压范围内的晶体结构和弹性模量,以及B1、B4和B8相结构的MgO的声速随压力的变化。利用准简谐近似下的Debye模型,通过拟合三阶Birch-Murnaghan物态方程模拟了高温效应并对三个相在高温高压下的相稳定性做了研究。本工作的计算结果与前人的理论和实验结果符合较好,说明第一性原理结合准简谐Debye模型能够比较准确的模拟矿物如MgO在高温高压下的热力学性质。     

MgO高温高压特性及相变的第一性原理研究

应用第一性原理密度泛函理论计算了MgO在零温(0K)下和0~200GPa静水压范围内的晶体结构和弹性模量,以及B1、B4和B8相结构的MgO的声速随压力的变化。利用准简谐近似下的Debye模型,通过拟合三阶Birch-Murnaghan物态方程模拟了高温效应并对三个相在高温高压下的相稳定性做了研究。本工作的计算结果与前人的理论和实验结果符合较好,说明第一性原理结合准简谐Debye模型能够比较准确的模拟矿物如MgO在高温高压下的热力学性质。     

The structure of a propagating MgAl2O4/MgO interface: linked atomic- and μm-scale mechanisms of interface motion

To understand how a new phase forms between two reactant layers, MgAl₂O₄ (spinel) has been grown between MgO (periclase) and Al₂O₃ (corundum) single crystals under defined temperature and load. Electron backscatter diffraction data show a topotaxial relationship between the MgO reactant and the MgAl₂O₄ reaction product. These MgAl₂O₄ grains are misoriented from perfect alignment with the MgO substrate by ~2–4°, with misorientation axes concentrated in the interface plane. Further study using atomic resolution scanning transmission electron microscopy shows that in 2D the MgAl₂O₄/MgO interface has a periodic configuration consisting of curved segments (convex towards MgO) joined by regularly spaced misfit dislocations occurring every ~4.5 nm (~23 atomic planes). This configuration is observed along the two equivalent [1 0 0] directions parallel to the MgAl₂O₄/MgO interface, indicating that the 3D geometry of the interface is a grid of convex protrusions of MgAl₂O₄ into MgO. At each minimum between the protrusions is a misfit dislocation. This geometry results from the coupling between long-range diffusion, which supplies Al³⁺ to and removes Mg²⁺ from the reaction interface, and interface reaction, in which climb of the misfit dislocations is the rate-limiting process. The extra oxygen atoms required for dislocation climb were likely derived from the reactant MgO, leaving behind oxygen vacancies that eventually form pores at the interface. The pores are dragged along by the propagating reaction interface, providing additional resistance to interface motion. The pinning effect of the pores leads to doming of the interface on the scale of individual grains.