CRYSTAL-STRUCTURE, THERMAL AND MAGNETIC-PROPERTIES OF LA4CO3O9 - PHASE-RELATIONS FOR LA4CO3O10-DELTA THAN-OR-EQUAL-TO-DELTA-LESS-THAN-OR-EQUAL-TO-1.00) AT 673 K

Phase relations and reoxidation behaviour is reported for samples with nominal composition La4Co3O10-delta (0.00 less than or equal to delta less than or equal to 1.00) synthesized by isothermal reduction at 67 3 K. The crystal structure of La4Co3O9 has been determined on the basi s of high-resolution powder X-ray diffraction and neutron diffraction data. The space group is Pnma, a = 545.72 pm, b = 2855.3 pm: c = 565.4 2 pm at RT; R-wp(PXD) = 6.2%, R-wp(PND) = 9.0%, R-p(PXD) = 4.4%, R-p(P ND) = 7.0%. Reduction of La4Co3O10 into La4Co3O9 leads to ordering of oxygen vacancies. Chains of corner-sharing CoO4 tetrahedra running alo ng [100] are formed within the central-layer of each triple perovskite type layer of the Ruddlesden-Popper type structure of La4Co3O10, wher eas the top and bottom layers retain the perovskite type arrangement o f corner-sharing CoO6 octahedra. La4Co3O9 orders antiferromagnetically at temperatures below T-N = 303 +/- 5 K. The magnetic structure is de scribed on the basis of powder neutron diffraction data. The magnetic moments mu(tet) = 2.6 +/- 0.1 mu(B) and mu(oct) = 3.0 +/- 0.1 mu(B) co rrespond fairly well to spin only values for high-spin Co-II.