Electron Density Distribution in Mn₄Si₇

Single crystal diffraction measurements were successfully carried out for spherical fine grains grown as single crystals of 0.05–0.2 mm in diameter. Local modulations in the silicon layers were also observed by means of high-resolution electron microscopy. The metallic tin–flux technique was used for crystal growth. The Fourier synthesis and maximum entropy method (MEM) were applied to x-ray diffraction data to obtain electron density distribution maps. Mn₄Si₇ is one of the most promising p-type thermoelectrics useable from 400 K to 700 K. The crystal structure is described in terms of a chimney-ladder structure. The doping effect, by which the system becomes n-type and a structure modulation occurs, was reported by our group previously. The resultant electron density maps were compared with those from the band calculation. The MEM calculation shows the displacement of silicon positions.