14:30 〜 14:45
[SIT16-04] Stability and elastic property of C37-type Ni2Si under high-pressure
キーワード：惑星コア、弾性特性、相安定性、高圧
Metallic cores of Earth and other terrestrial planets such as Mercury, Venus, and Mars likely contain light elements in addition to iron and nickel [1]. The metallic cores have been initially molten just after planetary formation and then partially or fully solidified to form inner cores through their cooling history. Depending on the cores' composition, the solid inner cores are also believed to include light elements. Therefore, it is crucial to understand the crystal structures and elastic properties of FeNi-light element alloys under high-pressure and -temperature conditions for comprehending the internal structure and dynamics of the planetary cores. Recently, it was reported that Fe2S and Fe2P both adopt the C37-type structure (Pnma, Orthorhombic) under high-pressure and high-temperature conditions, suggesting the possible presence of C37-(Fe, Ni)2(Si, P, S) phase in the planetary solid inner cores [2-4]. Here, we examined the phase stability and elastic property of Ni2Si, an end member of the C37 phase, up to 119 GPa and 2040 K by X-ray diffraction (XRD) measurements.
We have carried out XRD measurements under high-pressure and -temperature conditions using laser-heated diamond anvil cells at the SPring-8 beamline BL10XU. Ni2Si is in the C37-type structure at ambient conditions. We found the C37-type phase stable up to at least 119 GPa and 2040 K. The equation of state for the C37-type Ni2Si was determined as the volume of 131.8(2) Å3, the bulk modulus of 212(3) GPa, and its pressure derivative of 4.0(1) at zero pressure and 300 K. The elastic properties of C37-type Ni2Si are similar to those of C37-type Fe2S and Fe2P. However, Fe2S exhibits a systematically larger volume by ~3% than Ni2Si and Fe2P, which cannot be explained solely by differences in atomic sizes constituting each phase. Therefore, it is indicated that non-negligible differences in the bonding state or electronic state of Si or P and S may occur within the C37-type structure. This may limit the range of solid solution formation in the C37-(Fe, Ni)2(Si, P, S) phase under the relevant P-T conditions of planetary cores.
[1] McDonough. Treatise on Geochemistry, 3, 559–577 (2014).
[2] Tateno et al., Geophys. Res. Lett., 46(21), 11944-11949 (2019)
[3] Nakajima et al., Ame. Mineral., 105(11), 1752-1755 (2020).
[4] Oka et al., Ame. Mineral., 107(7), 1249-1253 (2022)
We have carried out XRD measurements under high-pressure and -temperature conditions using laser-heated diamond anvil cells at the SPring-8 beamline BL10XU. Ni2Si is in the C37-type structure at ambient conditions. We found the C37-type phase stable up to at least 119 GPa and 2040 K. The equation of state for the C37-type Ni2Si was determined as the volume of 131.8(2) Å3, the bulk modulus of 212(3) GPa, and its pressure derivative of 4.0(1) at zero pressure and 300 K. The elastic properties of C37-type Ni2Si are similar to those of C37-type Fe2S and Fe2P. However, Fe2S exhibits a systematically larger volume by ~3% than Ni2Si and Fe2P, which cannot be explained solely by differences in atomic sizes constituting each phase. Therefore, it is indicated that non-negligible differences in the bonding state or electronic state of Si or P and S may occur within the C37-type structure. This may limit the range of solid solution formation in the C37-(Fe, Ni)2(Si, P, S) phase under the relevant P-T conditions of planetary cores.
[1] McDonough. Treatise on Geochemistry, 3, 559–577 (2014).
[2] Tateno et al., Geophys. Res. Lett., 46(21), 11944-11949 (2019)
[3] Nakajima et al., Ame. Mineral., 105(11), 1752-1755 (2020).
[4] Oka et al., Ame. Mineral., 107(7), 1249-1253 (2022)