Crystal Structure of Ca4.78Cu6O11.60
Résumé
The crystal structure of Ca4.78Cu6O11.60 (crystal system, monoclinic; space group P2/c, Z=4, ρ=4.48(2)g/cm3, a=10.9456(4) Å, b=6.3192(2) Å, c=16.8408(5) Å, and β=104.952(2)°) has been solved and refined using X-ray and neutron powder diffraction combined with Rietveld analysis. It is closely related to the NaCuO2-type structure. The phase stoichiometry and the displacements of atoms with respect to their positions in the previously reported substructure (crystal system, orthorhombic; space group, Fmmm, a=2.807(1) Å, b=6.351(2) Å, and c=10.597(3) Å) are explained by the minimization of Ca-Ca repulsion and by a relaxation toward a more regular octahedral environment for Ca atoms. The substitution of Tl atoms for Ca atoms results in an increased thermal stability and in incommensurate structures with modulation vectors depending strongly on the Tl content.