Synthesis and structural study from X-ray powder diffraction of Pb0.5Th2(PO4)3

A new mixed lead thorium phosphate, Pb0.5Th2(PO4)3, has been isolated in the system PbO–ThO2–P2O5. Its crystal structure (monoclinic symmetry, a=17.459(1) A, b=6.8451(4) A, c=8.1438(5) A, β=101.247(5)°, space group C2/c) has been determined from conventional monochromatic X-ray powder diffraction data. The structure is related to the MITh2(PO4)3 structure type. Lead atoms are located in the channels parallel to the c axis, out of the twofold axis for 0.97 A, and are statistically distributed on a quarter of crystallographic positions. The thermal stability of this material is greater than that of the monazite-type compound PbTh(PO4)2.