Double selenates of rare earths and ammonium

Double selenates of rare earths with ammonium were prepared in result of crystallization. It is shown that NH4Ln(SeO4) · nH2O crystalline hydrates are presented by penta-and trihydrates. Existance of two modifications was revealed for NH4Ln(SeO4) · 5H2O: monoclinic form of NH4La(SeO4)2 · 5H2O, isostructural RbCe(SeO4)2 · 5H2O, and earlier unknown rhombic form of salts with Ln = Pr, Nd. Trihydrates with Ln = Sm-Yb belong to structural type of RbNd(SeO4)2 · 3H2O. Anhydrous salts NH4Ln(SeO4)2 are isostructural with monoclinic KNd(SO4)2 modification. Lattice parameters of binary selenates are presented