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Preparation and crystal structures of La2Cu1−xLixO4 solid solutions and evidence for a new oxide with a defect K2NiF4 structure: La4Li2O7

1989; Elsevier BV; Volume: 80; Issue: 1 Linguagem: Inglês

10.1016/0022-4596(89)90037-6

1095-726X

J. Paul Attfield, Gérard Férey,

Physics of Superconductivity and Magnetism

La2Cu1−xLixO4 (0 < x < 0.50) solid solutions have been prepared and characterized by powder neutron diffraction at 5 K. They possess the orthorhombic La2CuO4 structure up to x = 0.10 at room temperature and to above x = 0.25 at 5 K. An ordering of copper and lithium cations is observed close to x = 0.5 and anisotropic broadening of the superstructure peaks indicates that the ordering is of long range in the xy plane, but is of much shorter range between planes due to stacking faults. Partial refinements of ordered structures with x = 0.46 and 0.50 are presented. No significant evidence for oxygen vacancies is apparent from any of the refinements or analytical results. Hence these materials are remarkable for their Cu(III) contents (98(5)% at x = 0.50 from iodometric titrations) in view of their preparation in air at 900–950°C followed by quenching to room temperature. A new phase with a defect K2NiF4 structure has been identified as La4Li2O7 (a = 3.659(2)Å, c = 13.232(8)Å). A structure refinement shows that the oxygen vacancies are in the z = 0 plane.