Silicon and magnesium diffusion in a single crystal of MgSiO₃perovskite

Abstract

[1] Si and Mg self-diffusion coefficients were measured simultaneously in single crystals of MgSiO 3 perovskite under lower mantle conditions. There is little difference in Si volume diffusivity measured directly using single crystals (this study) and those retrieved from experiments with polycrystals (earlier studies). This agreement between studies establishes the reliability of Si diffusion coefficients measured in perovskite. Within the uncertainties of our measurements, no anisotropy in the diffusion of either Si or Mg could be resolved. À11 m 2 /s for Mg, DH = 308 kJ/mol for Si, and 305 kJ/mol for Mg. Mg diffusivity in MgSiO 3 perovskite is distinctly lower than those measured in olivine, wadsleyite, and ringwoodite. We find that Mg has very similar diffusivity to Si in perovskite. As a consequence, the rheological properties of the lower mantle may be controlled by the coupled motion of Si and Mg. A point defect-based model is discussed that may account for the diffusion behavior of Si and Mg in MgSiO 3 perovskite. Our data indicate that, within realistic ranges of temperature, grain size, and state of stress, both diffusion creep as well as dislocation creep may be observed in the lower mantle.

Application of the cBΩ model to the calculation of diffusion parameters of Si in silicates

“…Nevertheless, the thermodynamic wadsleyite (10–20 GPa and 1000–1900 K) and ringwoodite (16–24 GPa and 1000–1900 K) calculations are slightly lower than those experimentally obtained [ Shimojuku et al ., ]. The experimental determinations for Si self‐diffusion in MgSiO 3 perovskite are completely close to each other [ Yamazaki et al ., ; Dobson et al ., ; Xu et al ., ] at 25 GPa. These results match our thermodynamic calculations at the 1600–2100 K temperature range (Figure b) if one considers the experimental error in the elastic data at high pressure.…”

96Zr Tracer Diffusion in AZrO3 (A = Ca, Sr, Ba)

“…Figure 7 implies that Zr 4+ in the AZrO 3 materials is as slow as in ZrO 2 -based oxides, with fluorite structure revealing the low mobility of B-site in the cubic and orthorhombic AZrO 3 perovskites. [10]; (6) Si in MgSiO 3 [39]; (7) 49 Ti in sc (La,Sr)TiO 3 [25]; (8) Zr in sc BaTiO 3 [12]; (9) The low mobility of Zr 4+ in the current materials, evident by the comparison in Figure 7, is beneficial with respect to the chemical stability in potential gradients, but will shift the sintering temperature of the materials to high temperatures. High sintering temperatures are needed to obtain high density AZrO 3 materials, reflecting that the slow diffusion of Zr 4+ is rate limiting for the sintering [8].…”

“…Abbreviations: ppolycrystalline; sc-single crystal; c-cubic; b-bulk; gb-grain boundaries. (1) Ho in p BaTiO3 gb [11]; (2) Ho in p BaTiO3 b [11]; (3) Ni in p Ba(Ho,Ti)O3 [10]; (4) Ni in sc BaTiO3 [10]; (5) Ni in p BaTiO3 [10]; (6) Si in MgSiO3 [39]; (7) 49 Ti in sc (La,Sr)TiO3 [25]; (8) Zr in sc BaTiO3 [12]; (9) 141 Pr in LaFeO3 gb [40; (10) 141 Pr in LaCoO3 gb [40]; (11) Co in LaCoO3 gb [41]; (12) Cr in LaMnO3 [42];(13) Mn in LaCoO3 [43]; (14) Co in LaCoO3 b [41]; (15) 141 Pr in LaMnO3 [40]; (16) Co in GdCoO3 [44]; (17) Co in EuCoO3 [44]; (18) Co in SmCoO3 [44]; (19) Co in NdCoO3 [44]; (20) Co in PrCoO3 [44]; (21) 50 Cr in (La,Ca)CrO3 gb [45]; (22) Co in LaCoO3 [44]; (23) Mn in LaMnO3 b [42]; (24) Mn in LaMnO3 gb [42]; (25) Fe in LaFeO3 gb [46]; (26) Fe in LaFeO3 b [46]; (27) 141 Pr in LaCoO3 b [40]; (28) 141 Pr in LaFeO...…”

134Ba diffusion in polycrystalline BaMO3 (M = Ti, Zr, Ce)

“…13 The Ba lattice diffusion in BaMO 3 compared to the A-site cation diffusion in general in perovskites reported in the literature revealed no apparent trend. [26][27][28][29][30][31][32][33][34][35][36][37][38] In addition, the diffusion mechanisms for the data reported in the literature are usually not described. The point defect chemistry after materials processing determines the dominating diffusion mechanism as shown for BaZrO 3 .…”