2019 年 48 巻 1 号 p. 36-45
High-pressure and high-temperature experiments are vital tools for knowing the structure and evolutions of the Earth's deep interior. In this paper, I will introduce recent progress on the studies of the crystal structure, physical properties, and electronic state of iron and the phase relationships of minerals at lower mantle conditions. It was found that the partitioning and valence state of iron between minerals dramatically changes upon reaching the post-perovskite phase transition at the lowermost mantle. This may explain very sharp D″ discontinuity observed above core-mantle boundary. This research was achieved by a combination of the diamond anvil cell and transmission electron microscope techniques. Multiple analytical methods were combined to discover a new iron-oxide phase that might exist in the lower mantle. Relics of this phase may be found as inclusions in diamonds formed in the deep mantle. In situ high-pressure/high-temperature electrical conductivity measuring system was developed to experimentally investigate further Earth's internal structure. In addition to electrical conductivity, I have investigated the valence state, substitution site, and spin state of iron in lower mantle minerals by means of single crystal X-ray diffraction and Mössbauer spectroscopy. Results showed that the pyrolitic chemical model is consistent with the electrical conductivity of the ‘average’ lower mantle. New resistive heating techniques are now developed for use in diamond anvil cells that will, hopefully, guarantee homogeneous and stable heating.
