In situ transmission electron microscopy observation of an orientational order-disorder transition in Cd ₆ Eu and Cd ₆ Ce crystalline approximants

In situ transmission electron microscopy observations of Cd ₆ Eu and Cd ₆ Ce crystals show that the crystals undergo a structural phase transition from a face-centered cubic or a primitive cubic lattice to a body-centered cubic lattice at high temperatures, respectively. The phase transitions are found to be of an order-disorder type with respect to the orientation of the tetrahedron at the center of the icosahedral cluster.