Novel phase transition in the Cd6M intermetallics

X-ray and electron diffraction, electrical and thermal property experiments at low temperatures have unambiguously shown that Cd6Yb, Cd6Ca and Cd6Y intermetallics, which are cubic crystals with a∼1.5 nm, undergo a phase transition at 110, 100 and 164 K, respectively. The transitions are reasonably attributed to orientational ordering of Cd4 tetrahedra located at the center of icosahedral clusters; above the transition temperature the Cd4 tetrahedra are completely disordered resulting in a bcc structure (Im3-bar), whereas below the temperature they are ordered in a non-cubic structure of a doubled unit cell, i.e. 2ax2ax2a or 2ax2axa superlattice