Anhydrous Europium Phosphates: A Comprehensive Report on Syntheses, Crystal Structures, and Phase Relations

In the ternary system Eu/P/O the anhydrous phosphates Eu II 3 (PO 4 ) 2 , Eu II 3 Eu III (PO 4 ) 3 , Eu III 3 O 3 (PO 4 ), Eu III PO 4 , Eu III (PO 3 ) 3 , and Eu III P 5 O 14 exist at equilibrium conditions (ϑ ≈ 1000 °C). A superstructure model for Eu II 3 Eu III (PO 4 ) 3 [ Eulytite structure family, Fdd 2, Z = 24, a = 14.298(1) Å, b = 42.123(3) Å, c = 10.3887(9) Å] is proposed. The results of single‐crystal X‐ray diffraction (SXRD) studies on Eu II 10– x Eu III x (PO 4 ) 6 O 1+ x /2 ( x ≈ 1.5), Eu III 3 O 3 (PO 4 ) and ht ‐Eu III (PO 3 ) 3 are reported. The crystal structures of the thermodynamically metastable phases Eu III 2 P 4 O 13 (isotypic to Y III 2 P 4 O 13 ) and lt ‐Eu III (PO 3 ) 3 (isotypic to Gd III (PO 3 ) 3 ) were refined from X‐ray powder diffraction data (XRPD). According to our investigation for the oxide phosphide “Eu II 4 OP 2 ” an europium deficiency has to be assumed according to Eu II 4– x Eu III 2 x /3 OP 2 ( x ≈ 1.5).