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 AD,. 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 logp(O2). The experimental data are discussed on the basis of thermodynamic equilibrium calculations. (C) 2011 Elsevier B.V. All rights reserved.