[S-IT22] 核-マントルの相互作用と共進化

[SIT22-15] Effects of iron on the lattice thermal conductivity of lower mantle minerals evaluated by Ab initio anharmonic lattice dynamics simulations

*出倉 春彦¹、土屋 卓久^1,2 (1.愛媛大学地球深部ダイナミクス研究センター、2.東京工業大学地球生命研究所)

キーワード：下部マントル鉱物、格子熱伝導率、鉄固溶効果、第一原理計算

Determination of lattice thermal conductivity (κ_lat) of lower mantle (LM) minerals is a key to understanding the dynamics and evolution of the earth’s deep interior. Some recent experimental studies have shown that κ_lat of MgO and MgSiO₃ are substantially reduced by Fe incorporation (Manthilake et al., 2012; Goncharov et al., 2015; Ohta et al., 2017; Hsieh et al., 2017); Okuda et al. (2017) reported very weak effects on MgSiO₃ at lowermost mantle pressure. So, experimental results are still largely scattered and effects on Fe in κ_lat remains unclear. We recently established an ab initio technique to compute κ_lat of Fe-free systems based on the density-functional theory (DFT) combined with fully solving the phonon Boltzmann transport equation, which was successfully applied to MgO (Dekura and Tsuchiya, 2017). In this study, the technique is extended further to Fe-bearing systems, (Mg,Fe)SiO₃ bridgmanite (Brg) and (Mg,Fe)O ferropericlase (FP), combined with the internally consistent DFT+U technique (Wang et al., 2015). Calculations demonstrate strong solid solution effects in both Brg and FP. The effects of Fe are found to be caused mainly by the substantial changes in harmonic properties.