UC Irvine

We present neutron diffraction results for YbIn(Formula presented), and Rietveld refinements of the structure. The ground state has the same structure (C15B) as the high temperature state, so that the first-order phase transition at (Formula presented) K is indeed isomorphic, i.e., the lattice constant changes without a change of crystal symmetry. The site disorder and the diffraction linewidths decrease systematically on going from polycrystal samples with two transitions (at 40 and 70 K) to polycrystals with a single (40 K) transition to flux-grown single crystals with a sharp transition at 40 K. We argue that in site-disordered samples, the effect of doping Yb onto the In site is to increase (Formula presented) and cause the transition to become continuous. © 1996 The American Physical Society.