Synthesis and characterisation of Li11RE18M4O39−δ: RE = Nd or Sm; M = Al, Co or Fe

Abstract

Four new phases of general formula, Li₁₁RE₁₈M₄O_39−δ: REM = NdAl, NdCo, SmCo, SmFe, have been synthesised and characterised. The NdAl phase, and probably the others, is isostructural with the NdFe analogue, but some cation disorder and partial site occupancies prevent full structural refinement of powder neutron diffraction data. The NdCo phase also forms a solid solution with variable Li content (and charge compensation by either oxygen vacancies or variable transition metal oxidation state). The NdAl phase is a modest conductor of Li⁺ ions whereas the other three phases are electronic conductors, attributed to mixed valence of the transition metal ions. Subsolidus phase diagrams for the systems Li₂O–Nd₂O₃–Al₂O₃, ‘CoO’ have been determined and an additional new phase, LiCoNd₄O₈, which appears to have a K₂NiF₄-related superstructure, identified.