STRUCTURE AND THERMAL-BEHAVIOR OF GADOLINIUM(III)-SULFATE-OCTAHYDRATE GD2(SO4)3.8H2O

Gd2(SO4)3 . 8 H2O crystallizes monoclinic with space group C2/c and the lattice constants a = 13.531(7), b = 6.739(2), c = 18.294(7) angstrom, beta = 102.20(8)-degrees. In the structure Gd is coordinated by 4 oxygen atoms of crystal water and 4 oxygens of sulfate giving rise to a distorted square antiprism. During DTA-TG-experiments the title compound first loses crystal water in a two-step mechanism in the temperature range 130 - 306-degrees-C. The resulting Gd2(SO4)3 is amorphous and recrystallization occurs in the range 380-411-degrees-C. The so-obtained low-temperature modification beta-Gd2(SO4)3, undergoes a monotropic phase transition at about 750-degrees-C to the high-temperature form alpha-Gd2(SO4)3. The powder pattern of this modification was indexed based on monoclinic symmetry with space group C2/c and lattice constants a = 9.097(3), b = 14.345(5), c = 6.234(2) angstrom, beta = 97.75(8)-degrees. The high-temperature modification of gadolinium-sulfate shows decomposition to Gd2O2SO4 at 900-degrees-C and, subsequently, decomposition at 1200-degrees-C yields the formation of C-Gd2O3.