The chemistry of the phosphates of barium and tetravalent cations in the 1:1 stoichiometry

The chemistry of phosphates of barium and tetravalent cations [BaMIV(PO4)2] is reviewed. Such phosphates crystallise in the C2/m space group for MIV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P21/n space group for BaTh(PO4)2. The existence of BaMIV(PO4)2 in which MIV=Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaMIV(PO4)2 compounds and practical applications are briefly discussed.

Graphical representation of the variation of the unit-cell volume of BaMIV(PO4)2 as a function of the ionic radii of MIV cations. Such phosphates crystallise in the C2/m space group for MIV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P21/n space group for BaTh(PO4)2. The “BaCe(PO4)2” phosphate previously reported does not exist, as demonstrated in the present paper. Taking into account the present evidence, it can be concluded at this stage that the existence of other Ce(IV) phosphates obtained at high temperature and reported into the literature becomes doubtful. Figure optionsDownload as PowerPoint slide