Fig. 1.

(a) Half-cell view of the cubic Co₄Sb₁₂ skutterudite structure. The homo-nuclear Sb₄ rings are rectangular with an aspect ratio of ~0.95. (b) Half-cell view of the mixed-anion Co₄Sn₆Te₆ skutterudite. The replacement of Sn and Te on the Sb sites causes the octahedron to distort and the symmetry of the system to decrease to rhombohedral. The anion rings shift from rectangular to rhomboidal to account for the variable anion species (Sn₂Te₂).¹⁹