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The nuclear and magnetic structure of Sr2Fe205 has been determined by profile analysis of powder diffraction data. The results indicate disorder in the displacements of the iron atoms in the approximately tetrahedral sites in space group Icmm. The relationship of this structure to those of Ca2Fe206 (Pcmn) and Ca2(FeA1)20~ (Ibm2) is discussed. The values of the octahedral and tetrahedral site magnetic moments are compared with results for other Fem compounds.

The structure of tantalum oxynitride has been determined by the profile analysis of powder neutrondiffraction data collected at 4.2°K. The compound is monoclinic, space group P21/c, with a=4-9581, b=5"0267, c= 5"1752 A., and fl= 99.640 ° (4.2°K). Complete ordering of the anions occurs in alternate layers normal to the [100] direction and this ordering is consistent with calculated site potentials. Short nitrogen-nitrogen distances of 2.51 to 2"64 A~ are observed.

The intensities of low-angle neutron-diffraction peaks have been measured for the antiferromagnetic solids MnO, α-MnS, and NiO. From the reduced intensities of the (111) magnetic peaks the following covalency parameters have been derived: Aσ2 + 2Aπ2 + As2 = 3.5% (MnO); 7.6% (α-MnS); Aσ2 + As2 = 3.8% (NiO).

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