Non-stoichiometry, structural defects and properties of LaMnO3+δ with high δ values (0.11≤δ≤0.29)

摘要: Strongly oxygenated LaMnO3+δperovskites, with nominal MnIV contents up to 58%, have been prepared by thermal decomposition of metal citrates followed annealings either in air or under high oxygen pressure (200 bar). A high-resolution neutron powder diffraction study four representative samples 0.11≤δ≤0.29 reveals the presence both La and Mn vacancies. Contrary previous studies, it is found that there are a substantially higher proportion vacancies, depending rather sensitively on oxidation conditions. The state for calculated refined stoichiometry La1–xMn1–yO3 good agreement δ values previously determined analysis. Further this, also as increases Mn–O bond lengths shorten, Mn–O–Mn angles progressively increase perovskite structure becomes more regular, which consistent incorporation cations. vacancies (as much 13% pressure) perturbs conduction paths transport holes across Mn–O–Mn, weakening double-exchange interaction. This structural disorder explains observed decrease ferromagnetic Curie temperature (TC) increases.