Crystal structure, thermal and magnetic properties of La4Co3O9 . Phase relations for La4Co3O10−δ (0.00≤δ≤1.00) at 673 K

Abstract

Phase relations and reoxidation behaviour is reported for samples with nominal composition La₄Co₃O_{10– δ}(0.00≤delta;≤1.00) synthesized by isothermal reduction at 673 K. The crystal structure of La₄Co₃O₉ has been determined on the basis 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=565.42 pm at RT; R_wp(PXD)=6.2%,R_wp(PND)=9.0%, R_p(PXD)=4.4%,R_p(PND)=7.0%. Reduction of La₄Co₃O₁₀ into La₄Co₃O₉ leads to ordering of oxygen vacancies. Chains of corner-sharing CoO₄ tetrahedra running along [100] are formed within the central-layer of each triple perovskite type layer of the Ruddlesden–Popper type structure of La₄Co₃O₁₀ , whereas the top and bottom layers retain the perovskite type arrangement of corner-sharing CoO₆ octahedra. La₄Co₃O₉ orders antiferromagnetically at temperatures below T_N=303±5 K. The magnetic structure is described on the basis of powder neutron diffraction data. The magnetic moments µ_tet=2.6±0.1µ_B and µ_oct=3.0±0.1µ_B correspond fairly well to spin only values for high-spin Co^II .