The crystal and magnetic structures of the n = 3 Ruddlesden−Popper phase with the ideal composition Ca4Mn3O10 have been studied using X-ray and neutron powder diffraction. The crystal structure at 293 K is relatively insensitive to the partial pressure of oxygen used in sample preparation. A sample prepared in air showed an orthorhombic distortion (space group Pbca, a = 5.26557(12), b = 5.26039(11), c = 26.8276(5) Å) from the ideal n = 3 RP structure, as did a sample prepared under 800 atm of O2 pressure (a = 5.26005(4), b = 5.25569(4), c = 26.83543(20) Å). Both samples showed a magnetic phase transition at 115 K from a paramagnetic phase with extensive short-range spin ordering to a weakly ferromagnetic (μferro = 2 × 10-3 μB per Mn) low-temperature phase. The antiferromagnetic components of the atomic magnetic moments (2.23(2) μB per Mn) order in a G-type manner within each perovskite block, and the interblock coupling reflects the orthorhombic symmetry of the structure.

Sodium Hydride as a Powerful Reducing Agent for Topotactic Oxide Deintercalation: Synthesis and Characterization of the Nickel(I) Oxide LaNiO 2 . -Solid NaH serves as a novel reducing agent in the topotactic reduction of the Ni III perovskite oxide LaNiO 3 to the metastable Ni I phase LaNiO 2 (190-210 • C, evacuated Pyrex tube). A new tetragonal infinite-layer compound, NdNiO 2+x , is prepared by reduction of NdNiO 3 with NaH in the temp. range 160-210 • C. The LaNiO 2 phase crystallizes in the tetragonal space group P4/mmm. The simple infinite-layer model has to be significantly modified by a novel defect structure in which additional oxide ions are present in the space between the NiO 2 3− layers and produce both four-coordinate square-planar and five-coordinate square-pyramidal environments for Ni. -(HAYWARD, M. A.; GREEN, M. A.; ROSSEINSKY, M. J.; SLOAN, J.; J.

fCrystal chemistry and electronic properties of the n = 2 Ruddlesden-Popper manganates: unconventional C M R materials. ~o~f -~6~~0 d r n

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.