On the unit cell of Mallinckrodt's UO3

A new interpretation is offered for the data of Connolly, Acta Cryst. 12, 949 (1959), based on the quadratic form 10/sup 4/ sin/sup 2/ theta = q = 124.75(h/sup 2/ + k/sup 2/) + 2.5hk + 14.951/sup 2/, with h + k + 1 even. Positive features of the present interpretation are: the split lines stand out unambiguously as hkl,hk-barl doublets caused by pseudosymmetry; the number of molecules in the body-centered unit cell is Z = 16; the lattice is actually. face centered orthorhombic with a unit cell twice as large as the body-centered monoclinic unit cell; in the bodycentered description, the indices of all indexable lines follow the rather severe special restnictions of the spacegroup I4/sub 1//amd. (T.R.H.)