PHASE STUDY OF THE BINARY-SYSTEM LU2O3-LUF3 IN THE TEMPERATURE-RANGE 1000-1750 K

The phase diagram of the Lu2O3-LuF3 binary system was investigated by quantitative differential thermal analysis in the (1000-1750) K temper ature range, as well as by X-ray powder diffraction analysis. At tempe ratures lower than 1075 K, only the well-known compounds Lu2O3, LuOF, LuF3 and the series of fluorite-related orthorhombic vernier phases of the general composition LunOn-1Fn+2 with n = 5-10 were found to exist . At (1076 +/- 4) K an anion-deficient, fluorite-related and presumabl y monoclinic phase of the composition Lu(O,F)(1.91+/-0.01) is formed b y eutectoid reaction of Lu2O3 and LuOF. LuOF decomposes at (1079 +/- 4 ) K in a peritectoid reaction into Lu(O,F)(1.91+/-0.01) and the vernie r phase Lu10O9F12. All vernier phases were characterized with respect to their lattice parameters, and it was found that the lattice paramet ers depend linearly on composition. (C) 1997 Elsevier Science B.V.