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The infrared reflectance of iron was studied using high-pressure synchrotron radiation methods up to 50 GPa at room temperature in a diamond anvil cell of 1000-8000 [cm.sup.-1] (1.25-10[micro]m). The magnitude of the reflectivity shows a weak pressure dependence up to the transition from the body centered cubic ([alpha]) to hexagonal close packed ([epsilon]) phase transition, where a discontinuous change in both the slope and magnitude of the reflectivity was observed. Reflectance spectra were corrected for diamond absorption and treated with a Kramers-Kronig analysis to extract the optical constants; the emissivity of iron was derived from Kirchoff's law. The pressure and wavelength dependence of the emissivity is characterized by an empirical function for 1.5-1.9 [micro]m; this wavelength range is useful for spectroradiometric temperature measurements from 1000 K up to ~2500 K. [alpha]-Fe is a nonideal emitter; however, [epsilon]-Fe behaves as an almost perfect greybody in the infrared up to the highest pressures of the measurements. Temperature measurements based on the spectroradiometry of iron samples should take into account the wavelength dependent emissivity below the [alpha]-[epsilon] phase transition at ~13 GPa. OCIS codes: 260.3060, 160.3900.

The bulk moduli of defect structures may decrease as the defect concentration increases. However, the converse is true for the series of Sc(sub 1-x)S metal defect structures. This is revealed by a diamond anvil cell and synchrotron radiation experiment. Findings are in agreement with current electronic structure computations designed to probe the mechanism of ready metal atom loss from ScS at high temperatures and are in qualitative agreement with first-principles FLAPW computations.

CuS, or covellite (hexagonal symmetry), was compressed in a diamond anvil cell at room temperature up to a pressure of 45 GPa, and studied using x rays from both a Mo Kα source and a synchrotron. The x-ray diffraction spectrum of CuS disappears by about 18 GPa. The presence of Cu fluorescence lines in all spectra and the reappearance of diffraction lines upon decompression confirm that CuS undergoes reversible pressure-induced amorphization at this pressure. A third-order Birch–Murnaghan equation of state fit to the diffraction data below 11 GPa yields a bulk modulus of 89±10 GPa with a pressure derivative of -2±2 for covellite. Further compression up to 45 GPa shows three to four diffraction lines of very low intensity, implying some high pressure ‘‘ordering’’ of the amorphous phase. The Raman spectra obtained indicate that the changes in structure are probably due to the twisting or the distortion of covalently bonded CuS4–CuS4 units in different directions. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

ThO2 is an important material for understanding the heat budget of Earth’s mantle, as well as the stability of nuclear fuels at extreme conditions. We measured the in situ high-pressure, high-temperature phase behavior of ThO2 to ~60 GPa and ~2500 K. It undergoes a transition from the cubic fluorite-type structure (thorianite) to the orthorhombic α-PbCl2 cotunnite-type structure between 20 and 30 GPa at room temperature. Prior to the transition at room temperature, an increase in unit-cell volume is observed, which we interpret as anion sub-lattice disorder or pre-transformation “melting” (Boulfelfel et al. 2006). The thermal equation of state parameters for both thorianite [V0 = 26.379(7), K0 = 204(2), αKT = 0.0035(3)] and the high-pressure cotunnite-type phase [V0 = 24.75(6), K0 = 190(3), αKT = 0.0037(4)] are reported, holding K 0 ′ $\begin{array}{} K_0^{'} \end{array} $ fixed at 4. The similarity of these parameters suggests that the two phases behave similarly within the deep Earth. The lattice parameter ratios for the cotunnite-type phase change significantly with pressure, suggesting a different structure is stable at higher pressure. [ABSTRACT FROM AUTHOR]

Analysis of a predicted phase transformation of stishovite under high pressure, using Raman spectroscopy and a theoretical model, suggests that the structural transformation occurs at lower pressures than previously thought. Stishovite, a polymorph of silicon dioxide, undergoes phase transformation to the CaCl2 structure. The results suggest that free silica in the lower mantle will exist in the CaCl2 structure at low pressures, at depths greater than 1,200 km.

Magnesiowüstite [(Mg,Fe)O] is the second most abundant mineral of Earth's lower mantle. Understanding its stability under lower mantle conditions is crucial for interpreting the physical and chemical properties of the whole Earth. Previous studies in an externally heated diamond anvil cell suggested that magnesiowüstites decompose into two components, Fe-rich and Mg-rich magnesiowüstites at 86 GPa and 1,000 K. Here we report an in situ study of two magnesiowüstites [(Mg[sub 0.39], Fe[sub 0.61])O and (Mg[sub 0.25],Fe[sub 0.75])O] at pressures and temperatures that overlap with mantle conditions, using a laser-heated diamond anvil cell combined with synchrotron x-ray diffraction. Our results show that addition of Mg in wüstite (FeO) can stabilize the rock-salt structure to much higher pressures and temperatures. In contrast to the previous studies, our results indicate that Mg-rich magnesiowüstite is stable in the rock-salt structure in the lower mantle. The physical and chemical properties of magnesiowüstite should change gradually and continuously in the lower mantle, suggesting that it does not make a significant contribution to seismic-wave heterogeneity of the lower mantle. Stable Mg-rich magnesiowüstite in lower-most mantle can destabilize FeO in the core-mantle boundary region and remove FeO from the outer core. [ABSTRACT FROM AUTHOR]