PREPARATION AND STRUCTURE OF QUATERNARY MIXED SULFIDE LI(LU,M)S-2 (M=U, CE)

The Li(Lu,M)S-2 (M=U,Ce) compounds were prepared by the reaction of th e weighed mixture of Li2CO3, Lu2O3 and UO2 or CeO2 in a CS2+N-2 gas mi xture at 800 degrees C for 2 h. It was proved that a series of Li(LuyU 1-y)S-2 compounds showed an NaCl-type structure in a wide range of y v alues from 0.2 to 0.8, while the ternary sulphides LiLuS2 and Li2US3 c rystallized in hexagonal alpha-NaFeO2-type structure (R(3) over bar m) and monoclinic structure (C2/m), respectively. The Rietveld refinemen t showed that the compound was Li1.5Lu0.5U0.5S2.5 with cubic lattice p arameter 5.420 Angstrom and that the space group was Fm3m with the fin al R-I value of 0.027. A series of Li(LuyCe1-y)S-2 compounds also show ed the NaCl structure in a range of y values from 0.4 to 0.8, though L iCeS2 adopts a Th3P4 structure. The final R-I value for the compound L i1.17Lu0.5Ce0.5S2.17 with cubic lattice parameter 5.531 Angstrom was 0 .052 after the Rietveld refinement. (C) 1998 Elsevier Science S.A.