Gd₅Si_4−<i>x</i>P_<i>x</i>: Targeted Structural Changes through Increase in Valence Electron Count

Phase transformations in the Gd5Si4-xPx system (0 ≤ x ≤ 2), studied through X-ray diffraction techniques, reveal an intimate coupling between the crystal structure and valence electron count. An increase in the valence electron count through P substitution results in breaking the interslab T−T dimers (dT−T = 3.74 Å; T is a mixture of Si and P) and shear movement of the ∝2[Gd5T4] slabs in Gd5Si2.75P1.25. The Gd5Si2.75P1.25 phase extends the existence of the orthorhombic Sm5Ge4-type structures to the valence electron count larger than 31 e−/formula unit. Tight-binding linear-muffin-tin-orbital calculations trace the origin of the T−T dimer cleavage in Gd5Si2.75P1.25 to a larger population of antibonding states within the dimers.