Structural characterisation and physical properties of LiMMnO4 (M=Cr, Ti) spinels

Abstract New spinel-type phases of general formula Li M MnO 4 ( M =Cr, Ti), derived from LiMn 2 O 4 by substitution of Mn 3+ by Cr 3+ or Mn 4+ by Ti 4+ , have been obtained and characterised. Neutron diffraction refinements confirm that both phases crystallise in the F d 3 m space group, giving the cation distributions [Li] 8 a [CrMn] 16 d O 4 and [Li 0.66 Ti 0.34 ] 8 a [Li 0.34 MnTi 0.66 ] 16 d O 4 . Electrical conductivity has been examined by various techniques showing that these materials behave as semiconductors. The electrochemical behaviour indicates different oxidation–reduction steps in both cases concomitant with the insertion/deinsertion of lithium in non-reversible processes. X-ray diffraction patterns show that the above process is topotactic in LiCrMnO 4 . Magnetic data and neutron diffraction measurements show that no long-range magnetic ordering is present, suggesting a spin-glass transition for M =Cr at low temperature, while for M =Ti the presence of non-magnetic ions in the octahedral sublattice provokes an inherent magnetic frustration.