DISTRIBUTION OF VALENCE ELECTRONS IN MG2SI

The integrated intensity of x-ray reflections was measured on single crystals and powder samples of Mg2Si. The single-crystal measurements were carried out on an absolute scale; they were affected by secondary as well as primary extinction. The dimensions of the coherently scattering domaines wore found to be about 10-3 cm. The deviations of experimental structure factors from theoretical ones for the reflections (111), (222), (331) and (422) are significant. The electron-density distribution calculated from the experimental structure factors indicates spherical magnesium ions but shows that the outer electron shells of the silicon ions are distorted towards the nearest magnesium neighbors, thus forming an electron bridge of 0.2 e/A3. The average charge density between the ions is 0.05 e/A3, which means that 8 electrons are distributed within the unit cell in regions between ions. From the minimum density between Mg and Si, the radii rMg = 1.00 A and rsi = 1.75 Å were found. The ionic charges were found to be approximately Mg+1-5 and Si-1. © 1969, Walter de Gruyter. All rights reserved.