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Rare earth substitution in scheelite

Journal of Inorganic and Nuclear Chemistry
Publication Date
DOI: 10.1016/0022-1902(69)90014-1


Abstract Substitution of calcium in scheelite by lanthanum and samarium with or without sodium was studied in the temperature range between 600° and 1150°C using quenching techniques. In the systems CaWO 4La 2(WO 4) 3 and CaWO 4Sm 2(WO 4) 3, complete series of solid solutions form above 1020°C, but in each system there is a phase boundary separating the tetragonal scheelite and the monoclinic defect scheelite, while in the systems CaWO 4NaLa(WO 4) 2 and CaWO 4NaSm(WO 4) 2, immiscibility gaps disappear at 825°C, and they do not have any detected phase change in the solid solutions. In the ternary system CaWO 4NaLa(WO 4) 2La 2(WO 4) 3, at 750°C, a three-phase region consisting of tetragonal scheelite, tetragonal disordered scheelite, and monoclinic defect scheelite occupies the central portion of the phase diagram. At 900°C, scheelite with either disordered scheelite or defect scheelite is the major phase assemblage; and at 1025°C, there are only one-phase regions, the tetragonal solid solution transforming gradually to the monoclinic solid solution with increasing amount of La 2(WO 4) 3.

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