Crystal structures and electron-density distributions of Y(Fe, M)12 (M = Si, Ti, V, Cr, Mo, and W) determined by Rietveld and MEM analyses

The crystal structures of Y(Fe, M)12 (where M = Si, Ti, V, Cr, Mo, and W) were investigated by Rietveld analyses, and electron-density distributions were estimated by the maximum entropy method. There were no substituting elements to distort the lattice similarly. While the sites arranged selectively according to the element did not move necessarily, the distance between two atoms in the 8i site (an iron dumbbell) could change freely. Electron-density distributions revealed isolated iron dumbbells and a bonding network between Y, 8f, and 8j sites. Moreover, the connection in an iron dumbbell was much stronger than any other connection. As the substituting amount of the tungsten element increases, the electron density at interstitial positions increases. However, the high electron density disappears by over-substitution. It was suggested that the network of 22-hedrons, which configured the Y, 8f, and 8j sites, correlates with the thermal stability of the ThMn12 structure.