Compressibility studies have been carried out on Ge–I (diamond-cubic structure) to 12.0 GPa; the results are in very good agreement with previous work. We confirm the recent report of a substantial lowering of the Ge I–II transition pressure in a nonhydrostatic pressure environment. We observe the Ge–II (200)-peak at 10.5±0.2 GPa in a more hydrostatic pressure environment and as low as 6.7 GPa when shear stresses are present. On release of pressure from above 11 GPa, we find that Ge–II converts predominantly into Ge–III when Ge–I and shear stresses are present and completely into Ge–III in the absence of Ge–I in a more hydrostatic pressure environment. This is contrary to what had been previously presumed.

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A facility is described which has been developed for the rapid acquisition of structural information through the use of heterochromatic synchrotron radiation from a sample pressurized in a diamond-anvil cell and simultaneously cooled to cryogenic temperature. The system employs a closed-cycle He refrigerator, which can be continuously operated, independent of any liquid cryogens, from a remote station. The compressive contact force between the diamonds, and hence the sample pressure, is also externally controlled, thereby providing remote control capabilities for both the pressure and temperature. NaCl has been used as an internal pressure calibrant and existing empirical equation-of-state calculations for NaCl have been extended to reduced temperatures for this purpose. Preliminary data on the lower pressure critical point associated with the isomorphic phase transition in Ce0.8Th0.1La0.1 are presented.