INVITED FEATURE PAPERS Influence of pressure on dislocation, disclination, and generalized- disclination structures of a {310}/[001] tilt grain boundary in MgO Xiao-Yu Sun a) Unité Matériaux et Transformations, UMR 8207 CNRS/Université Lille1, Villeneuve d’Ascq, France Vincent Taupin Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (LEM3), Université de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France Patrick Cordier Unité Matériaux et Transformations, UMR 8207 CNRS/Université Lille1, Villeneuve d’Ascq, France Claude Fressengeas Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (LEM3), Université de Lorraine/CNRS, Ile du Saulcy, 57045 Metz Cedex, France Bijaya B. Karki School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA; and Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA (Received 5 June 2016; accepted 7 September 2016) Due to gravitational self-compression, the pressure in planetary interiors can reach millions of times the atmospheric pressure. Such high pressure has a significant influence on their rheology. In the present paper, we focus on how pressure in the range of the Earth’s lower mantle may influence the structure of a MgO {310}/[001] tilt boundary. The defected structure of the grain boundary (GB) will be described through its dislocation, disclination, and generalized-disclination (g-disclination) density fields. At first, the strain and rotation fields in the boundary area at different pressures are derived from the discrete atomic positions simulated by first-principles calculations. For each pressure, the discontinuities of displacement, rotation, and strain in the boundary area are continuously rendered by dislocation, disclination, and g-disclination density fields, respectively. These density fields measured at different pressures are compared to provide understanding on how pressure does influence the GB structures in Earth materials. I. INTRODUCTION In the Earth’s mantle, with increasing depth, pressure increases rapidly, reaching values as high as 136 GPa at the base of the mantle. 1 These ultrahigh pressures have profound implications on the rheology of the Earth’s constituents that can be quite different from that observed at ordinary pressure. Therefore, it is of primary impor- tance to investigate the mechanical behavior of the high- pressure phases of the deep Earth to understand the structure and dynamics of the Earth’s interior. Below 670 km, the phase assemblages present in the Earth’s transition zone decompose into a mixture of silicates with the perovskite structure and magnesium oxides (containing some iron). The high-pressure behav- ior of periclase (MgO) is thus of major importance in the rheology of the Earth’s interior. MgO is an ionic solid, which is chemically and physically stable at high temper- atures and pressures. It can keep its NaCl-type structure up to 227 GPa confining pressure. 2 This unique structural stability makes MgO an ideal benchmark for investigat- ing the behavior of solids at extreme pressure conditions. The structure and elasticity of MgO at high pressure have been widely studied by using first-principles calculations. Indeed, pressure-induced variation of the elastic moduli arises from changes in the structure and nature of atomic bondings under pressure and from phase transforma- tions. 1 For instance, the individual elastic moduli of MgO throughout Earth’s mantle pressure regime have been obtained with density functional theory. It was found that the pressure-induced elastic anisotropy is preserved down to the Earth’s lowest mantle. 3 The pressure-induced phase transformation of MgO was compared with that of other ionic and solids. 4 The elastic moduli, the intrinsic anharmonic parameters, and the B1–B2 transition pressure of MgO were determined from ab initio calculations. Simulation results show that MgO keeps its NaCl-type Contributing Editor: Susan B. Sinnott a) Address all correspondence to this author. e-mail: xiaoyu.sun@univ-lille1.fr This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2016.346 3108 J. Mater. Res., Vol. 31, No. 20, Oct 28, 2016 Ó Materials Research Society 2016. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Downloaded from https://www.cambridge.org/core . IP address: 54.70.40.11, on 23 Dec 2018 at 07:05:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms . https://doi.org/10.1557/jmr.2016.346