Synthesis, crystal structure, and magnetic properties of La4Co3O10+delta (0.00 <=delta <= 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 inv estigated between 2 and 1000 K. Rietveld analysis of high resolution powder X-ray diffraction data reveals the crystal structure of La4Co3O10+delta (R uddlesden-Popper type phase; Lan+1ConO3n+1 with n=3) to be slightly monocli nically distorted, space group C2/m. The monoclinic distortion increases an d the unit cell volume decreases slightly on increasing nonstoichiometry, d elta. A structural phase transition, monoclinic to tetragonal, possibly via an intermediate orthorhombic state, occurs at 840 K. Magnetic susceptibili ty data indicate long-range antiferromagnetic ordering below T-N approximat e 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 c omparable to that described for LaCoO3, Field-dependent magnetic susceptibi lity is observed for delta>0.00 for T < 180 K. (C) 1998 Academic Press.