Crystal structure analysis of Na4Si4−xGex by single crystal X-ray diffraction

The black platelet or columnar single crystals of Na4Si4−xGex (x = 0-4) were obtained by heating a mixture of Si and Ge in a Na melt at 1173 K, followed by slow cooling to room temperature. X-ray diffraction analysis of the single crystals clarified the space groups of Na4Si4−xGex with x = 0-2.4 and 2.8-4.0 as C2/c and P21/c, respectively. The lattice parameters and cell volume discontinuously changed at around x = 2.6, while the volume of the [Si4−xGex] tetrahedrons monotonically increased with increase in x. The Si atoms in the Si1 site of Na4Si4 were preferentially replaced by Ge atoms.