STRUCTURE REFINEMENTS OF LICU2O2 AND LICU3O3 FROM NEUTRON POWDER DIFFRACTION DATA

In its inherent ability to discern light elements in a heavy-atom matrix, neutron powder diffraction has been used at room temperature to confirm structure hypotheses of LiCu2O2 (R(I) = 2.18%; R(P) = 4.21%) and LiCu3O3 (R(I) = 2.19%; R(P) = 5.45%), inferred from previous X-ray diffraction studies. LiCu2O2 is orthorhombic, described by the space group Pnma (Z = 4), as suggested from a structure determination from twin-crystal data. The cell parameters found were a = 5.7260(4) angstrom, b = 2.8587(2) angstrom and c = 12.4137(7) angstrom. The apparent tetragonal symmetry independently advocated must be definitively discarded as an artifact from twinning. LiCu3O3. Was successfully refined on a tetragonal cell-with a = 2.8142(1) angstrom and c = 8.8956(5) angstrom - in P4/mmm (Z = 1) using a single-crystal model. The data were insufficient to test any superstructure model.