A New Type of Divalent Europium Compound MEuPO4 (M = K,Rb, Cs), its Synthesis,Crystal Structure,and Properties

Phosphates MEuPO₄ with M = K, Rb, and Cs were synthesized by the reduction of EuPO₄ with alkali metal vapour under 1 Pa of argon pressure at 260–530°C in sealed tantalum or niobium lined glass tubes. All the compounds belong to the β-K₂SO₄ orthorhombic structure with a = 7.359(3), b = 9.630(4), c = 5.569(2) Å, V = 394.7(2) ų for KEuPO₄, a = 7.462(3), b = 9.797(3), c = 5.649(2) Å, V = 413.0(2) ų for RbEuPO₄ and a = 7.889(2), b = 10.099(2), c = 5.820(4) Å, V = 463.6(2) ų for CsEuPO₄. Samples are stable and not hygroscopic in air at room temperature but hydrolyse to Eu₅(PO₄)₃OH, hexagonal, a = 9.764(2), c = 7.262(2) Å, on heating in water and decompose to Eu₃(PO₄)₂, hexagonal, a = 5.393(1), c = 19.838(3) Å, under argon at ca. 600°C. All the five compounds are paramagnetic.