IMPORTANCE OF THE X4-RING ORBITALS FOR THE SEMICONDUCTING, METALLIC, OR SUPERCONDUCTING PROPERTIES OF SKUTTERUDITES MX3 AND RM4X12

To gain insight into the electronic properties of binary and ternary skutterudite (i.e., CoAs3-type) compounds, we performed tight-binding band electronic structure calculations on a prototype skutterudite La Fe4P12. The major contribution to the highest occupied band of LaFe4P12 comes from the orbitals of the P4 rings that form the phosphorus sublattice. Consequently, the superconductivity of LaFe4P,2 seems to be associated largely with the electrons of the phosphorus sublattice. Our calculations suggest that the t2g- and eg-block bands of all skutterudites should be separated by a band gap. Thus, skutterudites are expected to be semiconducting if their transition-metal electron count is d6 but metallic in other cases. © 1990, American Chemical Society. All rights reserved.