Phase formation in the systems Li2MoO4-K2MoO4-Ln2(MoO4)3 (Ln=La, Nd, Dy, Er) and properties of triple molybdates LiKLn2(MoO4)4

Subsolidus phase relations in the systems Li2MoO4-K2MoO4-Ln2(MoO4)3 (Ln=La, Nd, Dy, Er) were determined. Formation of LiKLn2(MoO4)4 was confirmed in the systems with Ln=Nd, Dy, Er at the LiLn(MoO4)2-KLn(MoO4)2 joins. No intermediate phases of other compositions were found. No triple molybdates exist in the system Li2MoO4-K2MoO4-La2(MoO4)3. The join LiLa(MoO4)2-KLa(MoO4)2 is characterized by formation of solid solutions. Triple molybdates LiKLn2(MoO4)4 for Ln=Nd-Lu, Y were synthesized by solid state reactions (single phases with ytterbium and lutetium were not prepared). Crystal and thermal data for these molybdates were determined. Compounds LiKLn2(MoO4)4 form isostructural series and crystallized in the monoclinic system with the unit cell parameters a=5.315-5.145A, b=12.857-12.437A, c=19.470-19.349A, β=92.26-92.98o. When heated, the compounds decompose in solid state to give corresponding double molybdates. The dome-shaped curve of the decomposition temperatures of LiMLn2(MoO4)4 has the maximum in the Gd-Tb-Dy region. While studying the system Li2MoO4-K2MoO4-Dy2(MoO4)3 we revealed a new low-temperature modification of KDy(MoO4)2 with the triclinic structure of α-KEu(MoO4)2 (a=11.177(2)A, b=5.249(1)A, c=6.859(1)A, α=112.33(2)o, β=111.48(1)o, γ=91.30(2)o, space group P1-bar , Z=2)