Experimental investigations on the electronic structure and the low-temperature stability of Cd-based quasicrystals and their 1/1 cubic approximants

Abstract

Valence band spectra of icosahedral quasicrystals and their 1/1 cubic approximants in the Cd-Yb and Cd-Ca systems are investigated systematically. A sharp Fermi edge, indicative of sizable density of states at the Fermi level (E _F ), is clearly observed for all the compounds and E _F is located not at the bottom of the pseudogap but at its shoulder. In addition, a peak structure appears just below E _F for the Cd-Ca system, which is also found for the Cd-Yb system when subtracting a Yb 4f derived doublet. Ca 2p-3d resonant photoemission spectroscopies on the Cd-Ca compounds reveal the existence of Ca 3d states at E _F , indicating that the 3d states do contribute to the peak structure at E _F , which is attributed to hybridization with the Cd sp states. The low-temperature structural properties of the Cd-based compounds are also reported. An occurrence of a structural phase transition at 110 K and 100 K for Cd₆Yb and Cd₆Ca, respectively, is well documented. The transitions are understood as a consequence of an orientational ordering of Cd₄ tetrahedron located at the center of the icosahedral clusters. It is suggested that two orientations of the Cd₄ tetrahedron alternatively occur along the [110] direction of the high temperature bcc phase.

Acknowledgements

This work was supported by the Solution Oriented Research for Science and Technology (SORST), Japan Science and Technology Agency.