[S-IT22] 核-マントルの相互作用と共進化

[SIT22-P18] First-principles study on the site occupancy of Fe³⁺ in ferropericlase (Mg,Fe)O

*藤谷 宝海¹、土屋 卓久¹ (1.愛媛大学地球深部ダイナミクス研究センター)

キーワード：Fe3+、フェロペリクレース、第一原理計算

A high vacancy concentration due to the extrinsic mechanism is considered to be reproduced rheological property of Earth’s lower mantle via diffusion creep (e.g., Ita and Cohen 1998). Charge unneutral Fe³⁺ is one of the major impurities to create vacancies as the following reaction 3Mg^× → 2Fe^. + V^''. It has been experimentally reported that the site occupancy of Fe³⁺ changes from the octahedral site to the tetrahedral in MgO with increasing pressure around 15 GPa (Otsuka et al., 2010), leading to a further increase of the vacancy concentration in the octahedral site. However, little is known about the effects of Fe³⁺/vacancy configuration and the spin transition on its site preference, the differences in chemical bonds around octahedral and tetrahedral Fe³⁺. In this study, we investigate Fe³⁺ bearing MgO by using first-principles calculation methods based on the density functional theory up to 150 GPa. The tetrahedral occupation of Fe³⁺ is so fur not found in all the defect configurations and pressure condition examined, being not consistent with experimental findings.