Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe

TL;DR

This study reveals that Yb in YbGaGe is nearly divalent with stable valence across conditions, and lattice disorder likely explains the near-zero thermal expansion observed.

Contribution

It provides direct evidence of Yb's valence state and links lattice disorder to NZTE, clarifying the mechanism behind thermal expansion behavior.

Findings

Yb is nearly divalent in YbGaGe

Valence remains stable with impurities and temperature

Lattice disorder correlates with NZTE

Abstract

While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.