Temperature-induced abrupt volume inflation in the mixed-valence ternary Zintl phase Yb8Ge3Sb5.

The Zintl phase, Yb8Ge3Sb5 exhibits a complex lattice response and an abrupt negative thermal expansion below 15 K – subtle structural changes before and after the transition are consistent with temperature-induced electron transfer from (to) Yb 4f bands to (from) Sb 5p and Ge 4p bands.