SYNTHESIS, STRUCTURE, AND PROPERTIES OF LASR3FE3-XGAXO10-DELTA - AN INTERMEDIATE FE3-STATE( SPIN)

The solid solubility of Ga in this solid solution extends to x = 2. A phase change occurs near the composition x = 1 from tetragonal to orth orhombic. A Rietveld X-ray powder diffraction structure determination of LaSr3FeGa2O9 indicates that Fe occupies the central octahedral inte rstice in the triple octahedral layer. Oxygen vacancies are present in the equatorial positions of the central octahedron and in the bridgin g oxygen positions. The phase change is driven by the increase of the c/a ratio of the tetragonal phase. The phases are antiferromagnets wit h Neel temperatures of 45 K for the tetragonal phases that go to zero for the orthorhombic phase. The effective magnetic moment for the tetr agonal phase is 6 mu(B) for high spin Fe3+. An intermediate spin state of 4 mu(B) is observed for the orthorhombic phase indicative of three unpaired electrons. (C) 1996 Academic Press, Inc.