Change in local environment upon quasicrystallization of Zr–Cu glassy alloys by addition ofPd and Pt

Abstract

The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structurein Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certaintemperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization isaccompanied by a significant change in the local environment around the Zr atoms and aslight change around the noble metal. However, the local environment around the Cu atomsremains almost the same during QC formation. It is suggested that two types of icosahedralpolyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formedaround the Zr atoms. The other is in a distorted state around the Cu atoms. We speculatethat the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral clusteras its core, and the QC grows via aggregation of possible clusters in the initialstage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedralclusters, facilitating the formation of the nucleus and growth of the QC phase.