The binary phase diagram CaF2-SrF2 was investigated by differential thermal analysis (DTA). Both substances exhibit unlimited mutual solubility with an azeotropic point showing a minimum melting temperature of T-min = 1373 degrees C for the composition Ca0.582Sr0.418F2. Close to this composition, homogeneous single crystals up to 30 mm diameter without remarkable segregation could be grown by the Czochralski method. (c) 2007 Elsevier B.V. All rights reserved.