Neutron Diffraction Study of Pb2Sr2HoCu3O8.

The title compound has been studied by neutron and X-ray diffraction. The overall symmetry was determined to be orthorhombic with lattice constants a = 5.378(3), b = 5.421(3) and c = 15.688(7) angstrom. Initial Rietveld refinements of the powder neutron data made in space group Cmmm showed that the oxygen atoms in the PbO layer are displaced from the 4k (00z) position. The final refinements were therefore done in space group P1BAR, with all atoms except the oxygen atoms in the PbO layer constrained to obey C-centering. The origin of the orthorhombic distortion of the unit cell was in this way found to be the distortion of the oxygen atoms in the PbO layer.