Order-disorder transition in the Cd-Ca cubic approximant

TL;DR

This study investigates the order-disorder transition in Cd-Ca cubic approximants of quasicrystals, using ab-initio calculations to model interactions and reveal a phase transition similar to an antiferromagnetic Ising model, with insights into the structure.

Contribution

The paper introduces an ab-initio derived model for the order-disorder transition in Cd-Ca alloys and proposes a canonical-cell decoration model for the icosahedral phase.

Findings

Identified an antiferromagnetic Ising model equivalent for the transition

Calculated transition temperature exceeds experimental observations

Discovered a canonical-cell decoration model for the phase

Abstract

Recent experiments discovered an order-disorder transition occuring at low temperatures in large unit 1/1 cell cubic approximants of the stable Cd-based binary alloy quasicrystals. The transition is related to correlations among orientational degrees of freedom whose separations are around 12 \AA. We analyze the interactions between the degrees of freedom using {\em ab-initio} calculations for Cd-Ca alloys and derive an equivalent antiferromagnetic Ising model which shows a similar phase transition. However, the calculated transition temperature is higher than observed experimentally, indicating that the actual structure and its order-disorder transition are more complex than originally proposed. A side-benefit of our study is the discovery of a canonical-cell decoration model for the Cd-Ca icosahedral phase.