The electronic layer of Mg found in the electron density distribution map obtained by the maximum entropy method

The electron density distribution of HCP (hexagonal close-packed) metal Mg is obtained for the first time by the maximum entropy method (MEM). The data used in the analysis are measured by a newly developed synchrotron x-ray powder diffraction with an imaging plate (IP) as a detector. Care is taken in the quality of the specimen and the high counting statistics of the measurement. In the MEM map of Mg, which is the electron density distribution map obtained by the MEM, a surplus of electron charge is seen around the tetrahedral sites (T sites) of the HCP structure, while the electron densities around the octahedral sites (O sites) are much less than the average density of inter-atomic sites. By these surplus electrons, Mg metal forms a honeycomb network in the base plane and shows a kind of electronic layer structure. Since there are no ambiguities of phase determination, it can be said that the MEM map of Mg is constructed purely depending on the experimental data and free from any structural models. In our previous work the same kind of honeycomb network was found in Be, which is also an HCP metal. There is a high possibility that such honeycomb network is one of the structural characteristics of pure HCP metals at the electronic level. More work has to be done to investigate such a possibility and the MEM analysis will play an important role in structural studies at the electronic level.