The electrical resistivity of pure solid and liquid Fe has been measured at pressures up to 7 GPa in a large volume cubic anvil press. In conjunction with the four‐wired method, a novel technique of potential lead attachment was employed to measure the resistivity of 0.020‐in‐diameter Fe wire samples. Both the temperature and pressure coefficients of resistivity have been determined for solid and liquid Fe. The temperature coefficients of resistivity (TCR) in the liquid state are of the order of 10−4 K−1 and show an abrupt increase at approximately 5.2 GPa corresponding to the δ‐γ‐liquid triple point. We have interpreted this discontinuity in the TCR to be a reflection of local atomic structure in the liquid state which is reminiscent of the parent solid structure. By analogy, this result can be applied to the geophysically more important γ‐ε‐liquid triple point. By examining the fundamental effects of pressure and temperature on the density of states function and their ranges we arrive at an estimate of 1.2–1.5 × 10−6 Ωm for the electrical resistivity of pure Fe at the pressures and temperatures expected in the Earth's core.

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Single crystals and polycrystalline samples of transparent calcite (Iceland spar) were used to investigate the effects of pressure (p), temperature (T), pressure beyond an accepted equilibrium value (Δp), and grain size (D) on the kinetics of the calcite–aragonite transformation. Transformed mass fractions x(t), produced after different times of exposure to constant pressure ranging from 14 to 25 kbar (1.4 to 2.5 GPa) and constant temperature from 300 to 600 °C, were determined from integrated X-ray peak intensities of the (012), (021), and (111) reflections of aragonite. Values for the rale constant K and the exponent n characterizing the transformation were computed from the x(t) data using Cahn's nucleation and growth model for solid–solid transformations. At 17 kbar(1.7 GPa), K(s−1) increases from 2.00 × 10−5 at 300 °C to 1.39 × 10−3 at 600 °C. The exponent n, of the order of 1, mostly <1, indicates that the nucleation stage is terminated rapidly by site saturation and that most of the transformation takes place thereafter by growth as expected from theory. For single crystals the relationship between x(t) and Δp, for a period of 1 hour is almost linear. At 600 °C the relative increase of x(t) amounts to 0.1 kbar−1 (1 × 107 Pa−1). For a given time, x increases nearly exponentially with T. The apparent activation energy for the transformation, at 17 kbar (1.7 GPa), is 16 kcal mol−1. For polycrystals x(t) decreases as [Formula: see text]. This somewhat surprising result may be related to deviatoric stresses and stress concentration by the already transformed volume fractions, which act as misfitting, ellipsoidal, inclusions.

The fluid encapsulation technique allows for simultaneous in situ pressure and temperature calibration, at present up to 6 GPa and 800 °C, using on-line data processing. Each experimental run is done quasi-isobarically with continuous variation of temperature. Temperature is determined by the thermal emf’s of S- or K-type thermocouples placed in contact with accepted standard calibration materials which undergo pressure and temperature dependent phase transitions. In the course of this study, the phase diagrams of Bi, Hg, Sn, Tl, Pb, and Fe have been reinvestigated and self-consistency between transitions of all of these materials was used to determine the p,T(emf) coordinations. Thermal emf’s, for the S-type thermocouple, are converted to temperature using a 20-degree polynomial that fits the IPTS-68 data to within 0.4 K and is continuously differentiable in the temperature range from 0 to 1705 °C.

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