Skutterudite

Lore & Background

Skutterudite has been known since the Middle Ages, when it was used in the production of smalt. Smaltite is an alternative name for the mineral. Notable occurrences include Cobalt, Ontario and Franklin, New Jersey, in the United States. The unit cell consists of a total of 32 atoms, arranged in eight smaller cubes composed of cobalt atoms, which form octahedra with cobalt at the center. Six of these cubes are filled with planar square rings of arsenic, each oriented parallel to one of the unit cell's edges. At the 2a Wyckoff position, there are two large structural voids—each approximately five angstroms in size—that can be filled with impurity atoms.

Reader's Guide

Skutterudite is significant both as a historical ore mineral and as a model for modern thermoelectric materials. Mined for cobalt and nickel with arsenic as a by-product, it has been used since the Middle Ages in smalt production. The structure features two large voids per unit cell that can accommodate impurity atoms, a property exploited in materials science. Materials with a skutterudite structure are studied as low-cost thermoelectric materials with low thermal conductivity. A relatively high dimensionless figure of merit has been observed in a polycrystalline skutterudite partially filled with ytterbium ions. The small-diameter but heavy ytterbium atoms partially occupy the voids in the CoSb3 host structure, resulting in low thermal conductivity values while favorable electronic properties are not substantially disrupted. This makes skutterudite a key subject in the search for efficient thermoelectric energy conversion.

Did You Know?

• High nickel varieties are referred to as nickel-skutterudite, previously chloanthite.
• The arsenic content gives a garlic odor when heated or crushed.