Laser-heated Diamond Cell Research Articles

Ultrahigh-Pressure Melting of Lead: A Multidisciplinary Study

Measurements of the melting temperature of lead, carried out to pressures of 1 megabar (10(11) pascal) and temperatures near 4000 kelvin by means of a laser-heated diamond cell, are in excellent agreement with the results of previous shock-wave experiments. The data are analyzed by means of first principles quantum mechanical calculations, and the agreement documents the reliability of current experimental and theoretical techniques for studies of melting at ultrahigh pressures. These studies have potentially wide-ranging applications, from planetary science to condensed matter physics.

Simulating the core‐mantle boundary: An experimental study of high‐pressure reactions between silicates and liquid iron

Experiments with the laser‐heated diamond cell show that (Mg,Fe)SiO3 perovskite reacts chemically with liquid iron at pressures greater than 70 GPa and temperatures above 3700 K. X‐ray diffraction analyses of quenched samples demonstrate that the reaction products include SiO2 stishovite and iron alloys (Fe,Mg)xO and FexSiy, at the interface between the Fe and silicate. Our results suggest that similar chemical reactions occur at the Earth's core‐mantle boundary, forming chemical heterogeneities composed of silicate‐rich and iron alloy‐rich regions in the D′ layer. This scenario is consistent with seismological observations.

Model calculations of the temperature distribution in the laser-heated diamond cell

Numerical calculations are used to simulate the steady-state temperature distribution achieved during cw laser heating of a dielectric sample inside the high-pressure diamond cell. According to the results, the temperature field is controlled in the radial direction by the dimension (profile) of the laser beam; in the axial direction it is controlled by heat loss to the diamond anvils. Thus, the peak temperature is approximately proportional to sample thickness. The temperature distribution is nearly Gaussian in both the radial and axial directions, especially near the center of the hot zone in the sample. For typical experimental conditions, peak temperatures exceeding 5000 K and temperature gradients of ∼108–109 K/m are expected, with radial and axial dimensions of the hot zone being ∼20 and ∼10 μm, respectively. These values are in accord with experimental measurements, and they imply that despite the high temperatures achieved inside the sample volume the surrounding diamond anvils remain essentially at ambient temperatures.

Effects of composition and high pressures on the electrical conductivity of Fe-rich (Mg, Fe)2SiO4 olivines and spinels

Synthetic olivines, with composition Fa50, Fa75 and Fa100, have been transformed into spinel in a laser-heated diamond-cell at pressures from 70 to 200 kbar and at a luminance temperature of about 1,200° C. The electrical conductivity σ was measured, at room temperature and up to 200 kbar, on olivine (Lacam 1982; 1983) and spinel (present study). The data obtained permit the following conclusions: a) Sample nature effect: under the same conditions (composition, pressure), the σ of spinel is more than three orders of magnitude of the σ of olivine. b) Composition effect: there are more than three orders of magnitude between the values of σ for spinels derived from initial compositions of Fa50 and Fa100, respectively. c) Pressure effect: The P-effect on σ is greater for olivines than for spinels.