A computer simulation study of the effect of pressure on Mg diffusion in forsterite

被引:21
作者
Bejina, Frederic [1 ]
Blanchard, Marc [2 ]
Wright, Kate [3 ]
Price, G. David [4 ]
机构
[1] Univ Toulouse, CNRS, IRD, OMP,Lab Mecanismes & Transferts Geol, F-31400 Toulouse, France
[2] Univ Paris 07, Univ Paris 06, CNRS, IMPMC,UMR 7590,IPGP, F-75015 Paris, France
[3] Curtin Univ Technol, Nanochem Res Inst, Perth, WA 6845, Australia
[4] UCL, Dept Earth Sci, London WC1E 6BT, England
关键词
Forsterite; Computational modeling; Point defect; Diffusion; Activation volume; FE-MG; CATION DIFFUSION; AB-INITIO; DIELECTRIC-CONSTANTS; LATTICE-DYNAMICS; HIGH-TEMPERATURE; POINT-DEFECTS; OLIVINE; MG2SIO4; INTERDIFFUSION;
D O I
10.1016/j.pepi.2008.04.008
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Computer simulation techniques were used to investigate the effect of pressure on magnesium diffusion in forsterite between 0 and 10 GPa. We studied the diffusion path along the c crystallographic axis (we always refer to the Pbnm system) via a vacancy mechanism. Using a Mott-Littleton approach within the code GULP, we were able to precisely map the diffusion path of a Mg vacancy and we found the activation energy, E = 3.97 eV at 0 GPa (with E-f = 3.35 eV for the formation energy and E-m = 0.62 eV for the migration) and E = 4.46eV at 10GPa (E-f = 3.81 eV and E-m = 0.65eV). Preliminary results using the supercell technique gave the same saddle point coordinates and energies. This saddle point of the Mg vacancy diffusion found with GULP was then introduced in an ab initio code, confirming the values of the migration energy both at 0 and 10GPa. We were therefore able to estimate the activation volume (Delta V) to be around 5 cm(3)/mol and d(Delta V)/dP similar or equal to 0. The effect of pressure applies mostly on defect formation and little on migration. (C) 2008 Elsevier B.V. All rights reserved.
引用
收藏
页码:13 / 19
页数:7
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