Phase formation in the systems Li 2MoO 4–K 2MoO 4– Ln2(MoO 4) 3 ( Ln=La, Nd, Dy, Er) and properties of triple molybdates LiK Ln2(MoO 4) 4

Abstract

Subsolidus phase relations in the systems Li 2MoO 4–K 2MoO 4– Ln 2(MoO 4) 3 ( Ln=La, Nd, Dy, Er) were determined. Formation of LiK Ln 2(MoO 4) 4 was confirmed in the systems with Ln=Nd, Dy, Er at the Li Ln(MoO 4) 2–K Ln(MoO 4) 2 joins. No intermediate phases of other compositions were found. No triple molybdates exist in the system Li 2MoO 4–K 2MoO 4–La 2(MoO 4) 3. The join LiLa(MoO 4) 2–KLa(MoO 4) 2 is characterized by formation of solid solutions. Triple molybdates LiK Ln 2(MoO 4) 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 LiK Ln 2(MoO 4) 4 form isostructural series and crystallized in the monoclinic system with the unit cell parameters a=5.315–5.145 Å, b=12.857–12.437 Å, c=19.470–19.349 Å, β=92.26–92.98°. When heated, the compounds decompose in solid state to give corresponding double molybdates. The dome-shaped curve of the decomposition temperatures of Li MLn 2(MoO 4) 4 has the maximum in the Gd–Tb–Dy region. While studying the system Li 2MoO 4–K 2MoO 4–Dy 2(MoO 4) 3 we revealed a new low-temperature modification of KDy(MoO 4) 2 with the triclinic structure of α-KEu(MoO 4) 2 1 1 Hereinafter, α refers to a low-temperature modification. ( a=11.177(2) Å, b=5.249(1) Å, c=6.859(1) Å, α=112.33(2)°, β=111.48(1)°, γ=91.30(2)°, space group P 1 ¯ , Z = 2 ).