The binary phase diagram YF3-GdF3 was studied by differential scanning calorimetry (DSC). Yttriurn fluoride and gadolinium fluoride show complete miscibility in all three phases (orthorhombic room temperature phase, trigonal or hexagonal high temperature phase, liquid). The transformations between room temperature and high temperature phases are of first order and occur at 1338.6 K (YF3) or 1174.8 K (GdF3). Melting points are 1403.1 K (YF3) or 1525.7 K (GdF3), respectively. The c(p)(T) curve of GdF3 shows a lambda shaped local maximum at 1333 K that might be related to a further solid phase transformation of second order. (C) 2007 Elsevier Ltd. All rights reserved.