Thermoelasticity of Hexagonal Close-Packed Iron from the Phonon Density of States

摘要: Iron is the main constituent in Earth’s core, along with ~5 to 10 wt% Ni and some light elements (e.g., H, C, O, Si, S). This thesis explores vibrational thermodynamic thermoelastic properties of pure hexagonal close-packed iron (e-Fe), an effort improve our understanding a significant fraction this remote region deep Earth turn, better constrain its composition. In order access e-Fe, we directly probed total phonon density states (DOS) by performing nuclear resonant inelastic x-ray scattering (NRIXS) situ diffraction (XRD) experiments at Sector 3-ID-B Advanced Photon Source (APS) Argonne National Laboratory. NRIXS XRD were collected over course ~14 days eleven compression points between 30 171 GPa, 300 K. Our measurements sample volume each point, long data-collection times high-energy resolution resulted highest statistical quality dataset type for e-Fe outer core pressures. Hydrostatic conditions achieved chamber smaller compressions (P ≤ 69 GPa) via loading neon pressure transmitting medium GeoSoilEnviroCARS (GSECARS) sector APS. For made P > was fully embedded boron epoxy, which served as medium. From measured DOS definitions, determined wide range parameters, including Lamb-Mossbauer factor; components specific heat capacity, free energy, entropy, internal kinetic energy; Debye sound velocity. Together volumes, shape these parameters gave rise number important conditions. example, velocity (vD) from low-energy volumes. vD related compressional shear velocities densities adiabatic bulk modulus. high-statistical places new tight constraint on dependence e-Fe’s Via comparison existing data alloys, investigate how nickel candidate affect iron. addition, explore effects temperature applying pressure- temperature-dependent elastic moduli theoretical calculations finite-strain model. Such models allow direct comparisons one-dimensional seismic solid inner Preliminary Reference Model). Next, energy thermal pressure, combine previously reported values electronic anharmonic pressures find e-Fe. found steady increase factor compression, suggests restricted atomic motions behavior high-pressure melting Gilvarry’s reformulation Lindemann’s criterion, used obtain curve up GPa. By anchoring experimentally considering effects, investigated inner–core boundary (ICB, = 330 GPa), where liquid are contact. Then, combining under ICB conditions, offers information about composition seismically inferred ICB. remained similar all points, while maximum (cutoff) increased regularly decreasing volume. As result, able describe generalized scaling law and, ambient Gruneisen parameter. We also mentioned determine commonly discussed parameter (γD), be ~10% than any given Finally, Mie-Gruneisen relationship approximate form empirical Lindemann predict estimate pressures, can compared previous results. use entropy particular, reduced isotopic partition function ratios (β-factors) provide partitioning equilibrium processes. product component expansion coefficient isothermal modulus, independent (volume) gives volume-dependent K established EOS definition.