Recent work by Gupta and Shen [Appl. Phys Lett. 58, 583 (1991)] has shown that in a nonhydrostatic environment, the frequency of the ruby R, line provides a reliable measure of the mean stress or pressure. When using the frequency of either the R, or R, line to measure pressure at nonambient temperature, it is necessary to know the temperature dependence of the line shift. Unfortunately, the shift of the R2 line with temperature has not been reported. The ruby R i and R2 fluorescence shifts have been determined as a function of temperature from 15 to 600 K. Both can be fitted very well to the simple cubic forms R,(T) =14423+4.49~10-~T-4.81~10-~T~+3.71~10-'T~ cm-' and R2(T) = 14 452 $3.00~ 10m2T-3.88x 10e4T2+2.55x lo-'T3 cm-'. From 300 to 600 K the shifts fit well to linear functions of temperature. In addition, it is found that the RI-R2 splitting changes by about 3 cm-' over the 600 K temperature range. Linewidths were found to vary both with temperature and from sample to sample.

The usefulness of a silicone oil, Dow Corning 200, as a pressure medium in diamond anvil cells has been investigated. Common indicators of deviatoric stresses on ruby, such as changes in the R-line widths and the R2-R1 peak separation, show that this fluid does not deviate from hydrostaticity up to ∼15 GPa (150 kbar). The behavior of silicone is found to be very similar to the commonly used 4:1 methanol:ethanol mixture, while being much easier to use because of its higher viscosity. This ease of use and excellent performance makes silicone fluid a superior pressure medium.

The effect of low concentrations of Y, Er, and Cr solutes on the amorphous‐to‐γ transformation and on the γ‐to‐α transformation in aluminum oxide has been studied in situ by time‐resolved reflectivity. The activation energies of the two transformations with these dopants are the same as in undoped alumina, being 4.1 ± 0.1 and 5.2 ± eV, respectively. Although not affecting the activation energies, Y, Er, and Cr do affect the transformation kinetics. Y and Cr ions decrease the γ‐to‐α transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as ∼6 ppm retard the γ‐to‐α transformation and concentrations of 32 ppm essentially stop the transformation occurring within the times and temperatures accessible within the present experiment, thereby preventing quantification of the effect of Er on the α‐phase transformation. Erbium also retards the amorphous‐to‐γ transformation relative to undoped alumina whereas yttrium and chromium accelerate it.

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