Temperature Dependence of Yb Valence in an Au–Al–Yb Intermediate-Valence Quasicrystal Investigated by Yb <i>L</i><sub>3</sub>-Edge X-ray Absorption Near-Edge Structure Spectroscopy

Abstract

In this paper, we investigate the temperature dependence of Yb valence in an Au–Al–Yb intermediate-valence quasicrystal by Yb L3-edge synchrotron X-ray absorption near-edge structure spectroscopy. The Yb valence of 2.61+ at room temperature decreases monotonically as the temperature decreases, indicating that the Yb ionic radius increases as the temperature decreases and is consistent with the anomalous suppression of the thermal shrinkage of this quasicrystal by cooling, as previously reported. The Yb valence changes by −0.053 on cooling from 298 to 2 K, and its change is more gradual on the high-temperature side than on the low-temperature side with the boundary around 200 K. Additionally, the effect of the changes in the Yb valence on the volume is quantitatively examined. The ratio of the volume changes due to the change in Yb valence per Yb atom, ΔVYb, to the amount of change in Yb valence, Δν, which is expressed as ΔVYb/Δν, was evaluated. The value of ΔVYb/Δν was estimated to be −2.8 Å3/unit Yb valence/Yb atom, whose value was close to that evaluated for YbInCu4.