Synthesis and x-ray study of fluorite related phases in the system Ho2O3WO3

The preparation and identification of three new fluorite related compounds in the system Ho2O3WO3 is described. Ho6WO12 is isostructural with other heavy rare earth tungstates and uranates of the same stoichiometry. It has a rhombohedral structure whose hexagonal cell parameters are ao = 9.755 ± 0.001Å and co = 9.308 ± 0.002Å. Ho14W4O33 was tentatively indexed on the hexagonal cell: ao = 9.752 ± 0.003Å and co = 18.769 ± 0.006Å. The major reflections of the third compound, Ho10W2O21, were indexed on the tetragonal pseudocell: ao = 5.287 ± 0.001Å and co = 5.268 ± 0.002Å, but the true structure has lower symmetry and/or a larger cell. The possible structural relation of Ho10W2O21 and Ho14W4O33 to pure rare earth oxides with the same metal-oxygen ratios (M4O7 and M6O11) is discussed.