Structural variations in Gd5Si4-xSnx: size vs. electronic effects

X-ray single crystal diffraction studies on the Gd5Si4-xSnx series with 0 <= x <= 3 revealed an increase in the interslab T-T (T= Si, Sri) dimer distances and transition from Gd5Si4-type structures for 0 <= x <= 1.5 (d(T-T) = 2.49-2.71 angstrom) to the Pu5Rh4-type structure for x = 2 (d(T-T) = 3.04 angstrom). The Ti5Ga4-type structure, which is a stuffed version of the hexagonal Mn5Si3 structure, was observed for the Gd5SiSn3 sample (x = 3). Tight-binding linear-muffin-tin-orbital (TB-LMTO) calculations on Gd5Si2Sn2 show that the interslab (T1-T1) dimer stretching and the structural transition from the Gd5Si4-type to the Pu5Rh4-type results from the influence of the 5p atomic orbital energy and the larger size of the Sn atoms on the electronic structure, as compared to the Si and Ge atoms in Gd5Si4 and Gd5Si2Ge2.