Review: Coefficients for Stress, Temperature, and Composition Effects in Fluorescence Measurements of Alumina
Robert F. Cook, Chris A. Michaels
The numerical coefficients linearly relating the effects of stress (including pressure), temperature, and composition to shifts in the energies of the Cr-related fluorescence in alumina (Al2O3) are reviewed. The primary focus is the shift of the R1 and R2 ruby fluorescence lines under conditions typical for stress determination in polycrystalline Al2O3. No significant experimental difference in the R1 and R2 responses is observed for hydrostatic stress (or pressure) conditions (average shift coefficient of about 7.6 cm−/GPa), changes in temperature (about 0.140 cm−/K), or variations in composition (about 120 cm−/mass fraction of Cr). There are significant differences in the R1 and R2 responses for nonhydrostatic stress conditions. In particular, for uniaxial stress along the a and c directions in the Al2O3 crystal, the R1 piezospectroscopic tensor coefficients (about 3.0 cm−/GPa and 1.6 GPa cm−/GPa, respectively) differ considerably, whereas the R2 coefficients (about 2.6 cm−/GPa and 2.3 GPa cm−/GPa, respectively) do not. Measurements of the piezospectroscopic tensor coefficients are shown to have interlaboratory relative consistency of about 4 % extending over 30 years, and are consistent with the scalar high-pressure measurements. Measurements of the temperature coefficients are shown to have interlaboratory relative consistency less than 1 % extending over 60 years. Fluorescence- based measurements of stress in polycrystalline Al2O3, although requiring temperature adjustment, are shown to have a relative uncertainty of about 2.5 %.