Thermoelastic properties of hollow sphere composites are studied based on the uniform matrix-field concept proposed here. Some connections between local thermal and mechanical fields produced by certain homogeneous bo...Thermoelastic properties of hollow sphere composites are studied based on the uniform matrix-field concept proposed here. Some connections between local thermal and mechanical fields produced by certain homogeneous boundary conditions are derived, and furthermore, exact relations are also obtained between the effective thermoelastic properties of the composites. For a macroscopically isotropic composite with a certain ratio of the outer radius to the inner radius, it is found that the effective bulk modulus and the linear coefficient of thermal expansion can be exactly determined, if the thermal expansion coefficient of the matrix and that of the sphere are the same.展开更多
Eckstrom-adcock iron carbide(Fe_(7)C_(3))is considered to be the main constituent of the Earth’s inner core due to its low shear wave velocity.However,the crystal structure of Fe_(7)C_(3)remains controversial and its...Eckstrom-adcock iron carbide(Fe_(7)C_(3))is considered to be the main constituent of the Earth’s inner core due to its low shear wave velocity.However,the crystal structure of Fe_(7)C_(3)remains controversial and its thermoelastic properties are not well constrained at high temperature and pressure.Based on the first-principles simulation method,we calculate the relative phase stability,equation of state,and sound velocity of Fe_(7)C_(3)under core condition.The results indicate that the orthorhombic phase of Fe_(7)C_(3)is stable under the core condition.While Fe_(7)C_(3)does reproduce the low shear wave velocity and high Poisson’s ratio of the inner core,its compressional wave velocity and density are 12%higher and 6%lower than those observed in seismic data,respectively.Therefore,we argue that carbon alone cannot completely explain the thermal properties of the inner core and the inclusion of other light elements may be required.展开更多
High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120 GPa pressure at zero temperature. The lattice co...High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120 GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO3 crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the O-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle PIT range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO3-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model （PREM） profile, respectively, supporting the possibility of a pure perovskite lower mantle model.展开更多
文摘Thermoelastic properties of hollow sphere composites are studied based on the uniform matrix-field concept proposed here. Some connections between local thermal and mechanical fields produced by certain homogeneous boundary conditions are derived, and furthermore, exact relations are also obtained between the effective thermoelastic properties of the composites. For a macroscopically isotropic composite with a certain ratio of the outer radius to the inner radius, it is found that the effective bulk modulus and the linear coefficient of thermal expansion can be exactly determined, if the thermal expansion coefficient of the matrix and that of the sphere are the same.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.41904085,41874103,and 42274124).
文摘Eckstrom-adcock iron carbide(Fe_(7)C_(3))is considered to be the main constituent of the Earth’s inner core due to its low shear wave velocity.However,the crystal structure of Fe_(7)C_(3)remains controversial and its thermoelastic properties are not well constrained at high temperature and pressure.Based on the first-principles simulation method,we calculate the relative phase stability,equation of state,and sound velocity of Fe_(7)C_(3)under core condition.The results indicate that the orthorhombic phase of Fe_(7)C_(3)is stable under the core condition.While Fe_(7)C_(3)does reproduce the low shear wave velocity and high Poisson’s ratio of the inner core,its compressional wave velocity and density are 12%higher and 6%lower than those observed in seismic data,respectively.Therefore,we argue that carbon alone cannot completely explain the thermal properties of the inner core and the inclusion of other light elements may be required.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40474033 and 10376024, and the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No 20050613017.
文摘High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120 GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO3 crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the O-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle PIT range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO3-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model （PREM） profile, respectively, supporting the possibility of a pure perovskite lower mantle model.
