X-ray determination of electron-density distributions in oxides, MgO, MnO, CoO, and NiO, and atomic scattering factors of their constituent atoms.

Abstract

Based on accurate X-ray diffraction intensity data collected from spherically shaped single crystals, detailed electron-density distributions have been studied for synthetic mono-oxides, Mg0 (periclase), Mn0 (manganosite) , CoO, and Ni0 (bunsenite) .Mg0 (Sanger, 1969; Vidal-Valat and Vidal,1978) , MnO, and Coo have the NaCI type structure at room temperature.Although Ni0 is rhombohedral below a Neel temperature 523°K (Rooksky, 1948;Vernon, 1970) due to antiferromagnetic distortion from a NaCI type structure, the distortion is negligible for X-ray studies, so we assumed the NaCI type structure for this oxide as well.The result has revealed, as shown below, the atomic net charge, radial distribution, asphericity of electron density, and experimental atomic scattering factors.Crystal structure refinement.The crystals used for the present study were synthesized by Bernoulli method.Spheres with radii 0.155 mm, 0.105, 0.10, and 0.105 were prepared respectively from transparent crystals of MgO, MnO, CoO, and Ni0 and used for X-ray study.These crystals are pure and homogeneous within the analytical accuracy of EPMA, although trace amounts of Mn203 or Mn0.4 were detected from one of the Mn0 crystals by wet chemical analysis.The space group is Fm3m and the cell dimensions obtained from single crystal diffractometry (graphite monochromatized Mo Ka) are: a= 4.217(1)A for MgO; a=4.446 (1) for MnO; a=4.263 (1) for CoO; a-4.178(1) for NiO.The w-20 technique was used to collect, at temperature 23.5±0.5°C, intensity data up to 20=157°, involving all equivalent reflections; a Syntex P21 diffractometer was used with bisecting mode for 20_< 134° and parallel one for 134°<20< 157°.Of a total of 1200-1600 reflections measured for each of the four materials, independent reflections, 64, 74, 66 and 64 respectively for MgO, MnO, CoO, and NiO, were used for respective refinements after averaging all equivalent reflections.Each set of intensities was corrected for Lorentz