Intermediate-valence quasicrystal of a Cd-Yb alloy under pressure

Abstract

A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Yb quasicrystal. In this system, each quasiperiodic lattice point has a charge degree of freedom. Yb L III x-ray absorption spectroscopy experiments demonstrate that the Yb valence increases continuously upon compression from a divalent state at ambient pressure and reaches 2.33 at 31.7 GPa. A comparison study to the crystalline approximant suggests that the quasiperiodically arranged Yb ions have a homogeneous intermediate valence that takes a valence fluctuation state under pressure.

Magnetism in icosahedral quasicrystals: current status and open questions

“…Magnetic susceptibility measurements at high temperature found very similar behavior for both the quasicrystal and approximant and fits using the Curie–Weiss law to the data yielded effective moments of 3.91 /Yb(3.96 /Yb) and Weiss temperatures of –153 K(–117 K) for the quasicrystal (approximant). This is in striking contrast to the absence of a local moment for in the quasicrystal and approximant at ambient pressure, although intermediate valence behavior has been observed in Yb-Cd and Yb-Mg-Cd quasicrystals under applied pressure [102–104]. The effective moments for the Yb-Au-Al systems are intermediate between and , classifying them as mixed valent as confirmed by x-ray absorption near edge structure measurements [101].…”

In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal

“…Such a difference can not be explained solely by considering the differences in bulk moduli. Another important difference to be pointed out is the mixed valence character of Yb atoms [26]. Nozawa and Ishii [19][20][21] have investigated the P dependence of the tetrahedral configurations using a first-principles density-functional calculation.…”

Intermediate-Valence Quasicrystals of Yb-Based Alloys Under Pressure

“…Like i-CdYb, the divalent peak decreases upon compression and a trivalent component appears around 8.944 keV. Using a procedure similar to our previous report, 1) the mean valence at each pressure is determined by fitting each spectrum with the sum of the divalent and trivalent components, which are expressed as a combination of an asymmetric Gaussian and an arctangent function, respectively, and then calculating the mean valence from the intensity ratio of these two components. Figure 3 shows the pressure dependence of the mean valence.…”

“…However, for i-CdYb, an investigation of the volume compression and a comparison study on the crystalline approximant both suggest valence fluctuation. 1) It is considered that quasicrystals with various electronic structures should be realized by changing the strength of electron correlations upon compression. For example, in a case of valence fluctuation, a large density of state (DOS) due to the 4 f state should appear around the Fermi level.…”

“…1) Yb L III -edge x-ray absorption spectroscopy experiments demonstrated that the Yb valence increases continuously upon compression from the divalent state at ambient pressure, and reaches a valence of 2.33 at 31.7 GPa. This result is attributed to the characteristics of the Yb ion; the ionic radius decreases as divalent Yb shifts to the trivalent state.…”