On the effect of oxygen partial pressure on the chromium distribution coefficient in melt-grown ruby crystals

Small ruby crystals were grown by the Czochralski technique in different atmospheres and their actual chromium content was analyzed by a wet chemical method. The chromium distribution coefficient k   was found to be strongly dependent on oxygen partial pressure pO2pO2. It ranges from k=0.3 in a reducing atmosphere to k=1.2 in a slightly oxidizing atmosphere and to a good approximation k   depends linearly on logpO2logpO2. The experimental data are discussed on the basis of thermodynamic equilibrium calculations.

► Melt growth of ruby single crystals. ► Chromium distribution coefficient depends nearly linearly on the logarithm of oxygen partial pressure during growth. ► Control of chromium valency. ► Option for homogeneous chromium distribution.