M'-RTAO(4) SYNTHESIS - ACTIVATION OF THE PRECURSOR OXIDES BY THE REACTION FLUX

Studies of the M'-RTaO(4) (R = Gd, Y, Lu) phosphor synthesis reaction show that, contrary to previous views, the flux (e.g., Li2SO4, LiCl, N a2SO4) serves as an important reactant. Through a combination of techn iques (DTA, TGA, XRPD, and mass balance), we find that close to its me lting point, the flux reacts exothermically with the blended tantalum and yttrium oxides to give intermediate compounds. These reactive inte rmediates then combine to make M'-RTaO(4) and to regenerate the flux. Thus, the flux serves a dual purpose; it first activates the oxide rea ction mixture and then serves as a classical flux in the growth of RTa O(4) crystals. In light of this discovery, a more appropriate term for these flux compounds is catalyst or reactive flux because they facili tate the synthesis of RTaO, through chemical reaction. (C) 1995 Academ ic Press, Inc.