Structure refinements of LiCu2O2 and LiCu3O3 from neutron powder diffraction data

Abstract 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 LiCu 2 O 2 ( R I = 2.18%; R P = 4.21%) and LiCu 3 O 3 ( R I = 2.19%; R rmP = 5.45%), inferred from previous X-ray diffraction studies. LiCu 2 O 2 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) A , b=2.8587(2) A and c=12.4137(7) A . The apparent tetragonal symmetry independently advocated must be definitively discarded as an artifact from twinning. LiCu 3 O 3 was successfully refined on a tetragonal cell-with a=2.8142(1) A and c=8.8956(5) A -in P4/mmm (Z=1) using a single-crystal model. The data were insufficient to test any superstructure model.