Europium(II) phosphate is an inorganic compound of europium and phosphate with the chemical formula Eu3(PO4)2. It contains europium exclusively in the +2 oxidation state and is one of several anhydrous europium phosphates known in the Eu–P–O system.
Preparation Europium(II) phosphate can be prepared by reducing a mixture of europium(III) phosphate and europium(III) oxide in a stream of hydrogen at about 950 °C:
4 EuPO4 + Eu2O3 + 3 H2 → 2 Eu3(PO4)2 + 3 H2O
Earlier preparations of divalent europium compounds also obtained Eu3(PO4)2 under strongly reducing conditions.
A sol–gel route has also been used to prepare polycrystalline Eu3(PO4)2 for magnetic and magnetocaloric measurements.
Structure and properties Europium(II) phosphate is a grey crystalline solid. It crystallizes in the trigonal crystal system with the palmierite structure and is isotypic with Sr3(PO4)2.
The space group is Rm (No. 166). Refined lattice parameters are a = 5.3931(2) Å and c = 19.843(1) Å, with three formula units per unit cell.
The structure contains isolated PO4 tetrahedra and two crystallographically distinct europium sites. Its structural relationship to Sr3(PO4)2 reflects the similar ionic radii of Eu2+ and Sr2+.
Europium(II) phosphate is stable in air up to about 100 °C. At higher temperatures, oxidation of Eu2+ leads to formation of more oxidized europium phosphate phases.
Magnetic properties Eu3(PO4)2 is strongly magnetic because Eu2+ has a 4f7 electronic configuration. Early measurements identified the compound as ferromagnetic.
Later magnetic-susceptibility measurements found magnetic ordering below about 5 K. More recent work places the magnetic transition at approximately 5.9 K and describes it as a ferromagnetic-to-paramagnetic transition.
The 2023 study also reported a substantial low-temperature magnetocaloric effect, with a maximum magnetic entropy change of about 11.4 J kg−1 K−1 for a field change of 0–1 T near the magnetic ordering temperature.
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