Phase equilibria in the system NaAl(WO4)2–NaCr(WO4)2

The phase equilibria in the system NaAl(WO4)2–NaCr(WO4)2 are investigated. Nanopowders are synthesized in the whole concentration region from NaAl(WO4)2 to NaCr(WO4)2 by a co-precipitation method. Using X-ray, DTA, TEM and SEM analyses, three concentration regions in the system are established: single-phase region of NaAl1−хCrх(WO4)2 solid solutions (x is between 0 and 0.08), with monoclinic structure, space group C2/c; single-phase region of NaAl1−хCrх(WO4)2 solid solutions (x is between 0.40 and 1.0) with monoclinic structure, space group P2/c; and two-phase region, where the above mentioned phases crystallize simultaneously (x is between 0.08 and 0.40). The thermal behaviour of the two pure boundary phases, as well as the influence of chromium on the thermal stability and the structural characteristics of the solid solutions are discussed.

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► The phase equilibria in the system NaAl(WO4)2–NaCr(WO4)2 is established.
► The limit concentration of Cr in NaAl(WO4)2 and of Al in NaCr(WO4)2 are determined.
► The chromium influence on the stability and the structure are discussed.
► Cr-doped NaAl(WO4)2 nanopowder is obtained by co-precipitation method.