| Data are presented for the room-temperature, static compression of pyrite and iron to 40 GPa and 78 GPa, respectively, in a diamond-anvil cell with rare-gas solids as pressure-transmitting media. Compression data are also presented for solid argon to 78 GPa. This quasihydrostatic technique results in increased precision in the measurement of high pressures. The hydrostatic and nonhydrostatic pyrite isotherms deviate from each other throughout the whole pressure range studied, and this result indicates that the strength of pyrite increases continuously with confining pressure. The new zero-pressure isothermal bulk modulus, K(,0), and first pressure derivative, K'(,0), for (epsilon) iron are 192.7 ((+OR-)9.0) GPa and 4.29 ((+OR-)0.36), respectively; (epsilon) iron appears to be slightly less compressible under nonhydrostatic conditions. These results confirm that the absence of a soft medium in static compression experiments with the diamond-anvil cell results in an overestimate of the unit-cell volume (measured with the incident x-ray beam parallel to the load axis) for pressures calculated with the nonhydrostatic ruby calibration scale. It is found that, for (epsilon) iron, substantial compensation for this nonhydrostatic effect is implicit in the nonhydrostatic ruby pressure scale up to intermediate strains. No compensation is observed, however, with pyrite. The hydrostatic data for (epsilon) iron and the (epsilon)-iron isotherm derived from shock-wave experiments are in very close agreement. The Eulerian strain calculated for solid argon at 78 GPa is 0.5. From a least-squares fit of a finite-strain equation of state, (EOS) to the data (reduced to T = 0 with the Mie-Gruneisen EOS in the Debye approximation), the following limits have been placed on the parameters for the argon EOS at 0 K: K(,0) (GREATERTHEQ) 2.53 GPa, K(,0)' (LESSTHEQ) 9.19, and K(,0)K(,0)'' (GREATERTHEQ) -39.0. The experimental data for argon are also compared with calculations of the equation of state based on the Gordon-Kim electron-gas model. Both a pair-potential calculation, and a crystal model (including pairwise and many-body dispersion) are compared with the data of this study. These comparisons indicate that the effects of damping of the dispersion energy are more important than the inclusion of the higher-order, many-body contributions to the total electron-gas energy in solid argon.;A core model is constructed with the room-temperature compression data of iron and pyrite. On the assumption that the inner core is pure (epsilon) iron, and estimating the temperature at the inner-core boundary to be in the range 4000-6000 K, the volume thermal expansivity, (alpha), necessary to correct the PEM profile density up to that of the model is found to be significantly larger than previous estimates of (alpha) in the core. On the basis of this result, it appears that earth-model data are not compatible with a pure, (epsilon)-iron inner core. |
