Chromium influence on rhombohedral twinning in sapphire
Mechanical tests have been performed on sapphire doped with four different concentrations of chromium at temperatures between 800 and 1,000 °C. Samples were cut to favor rhombohedral twinning, which is the softest deformation mode of sapphire that inevitably leads to the failure of this material. We have investigated the effect of Cr doping on the rhombohedral twinning. The mechanical test results show that Cr atoms inhibit rhombohedral twinning, which appears to be athermal in the temperature range studied. An increase in the twinning-resolved stress is clearly observed. For 9,540 ppm Cr, the twinning-resolved stress becomes about three times higher than for undoped sapphire, potentially increasing its technological applications in the industry. The examination of lateral surfaces indicates that Cr atoms neither have influence on the twin width nor on the rhombohedral-twinning propagation. All these results have been properly explained within the model of Geipel et al.
KeywordsSapphire Chromium Concentration Basal Slip Adjacent Plane Zonal Dislocation
This work has been supported by the Ministry of Science and Technology (Government of Spain) through the project MAT2003-04199-CO2-02. Our colleague P. Veyssière passed away very recently. After a long time of friendship and collaborations, sadly this work is the last one that P. Veyssière signs with us. His great disposition, good character, and exceptional human and scientific value are remembered.
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