Soft phason modes inducing rhombohedral–icosahedral transformation

Abstract Phason modes responsible for the newly discovered rhombohedral–icosahedral structure transformation in Al—Cu—Fe alloy are discussed. By locking the phason strains to a special configuration giving the Ih→D3d symmetry change, we obtain a periodic structure with a prolate rhombohedral unit cell, which is a doubled version of the T 3 prolate rhombohedron obtained by the elementary face-matching rule. It is shown that the diffraction pattern for this periodic lattice is consistent with the diffuse scattering line shapes around the structural ‘transition’ temperature.