Synthesis, crystal structure, and magnetic properties of La4Co3O10+δ (0.00≤δ≤0.30)

The effects of nonstoichiometry on the crystal structure, thermal expansion, structural phase transitions, and magnetic properties of La4Co3O10+delta, 0.00 less than or equal to delta less than or equal to 0.30, have been investigated between 2 and 1000 K. Rietveld analysis of high resolution powder X-ray diffraction data reveals the crystal structure of La4Co3O10+delta (Ruddlesden-Popper type phase; Lan+1ConO3n+1 with n=3) to be slightly monoclinically distorted, space group C2/m. The monoclinic distortion increases and the unit cell volume decreases slightly on increasing nonstoichiometry, delta. A structural phase transition, monoclinic to tetragonal, possibly via an intermediate orthorhombic state, occurs at 840 K. Magnetic susceptibility data indicate long-range antiferromagnetic ordering below T-N approximate to 13 K, Above 20 K there are three temperature regimes with nearly Curie-Weiss paramagnetic behaviour for the magnetic susceptibility: 20-80 K, 100-450 K, 650-985 K. This indicates a temperature-induced change from a lower, possibly via an intermediate, to a higher spin configuration for Co-III comparable to that described for LaCoO3, Field-dependent magnetic susceptibility is observed for delta>0.00 for T < 180 K. (C) 1998 Academic Press.