SKUTTERUDITE VS. REO3 STRUCTURES FOR MX3 SOLIDS - ELECTRONIC REQUIREMENTS

Electronic band-structure calculations on ReO3 and CoP3 have been perf ormed to analyse the different structural preferences found for these two compounds. The electronic origin of these differences is associate d with the formation of the characteristic non-metal four-membered rin gs of the skutterudite structure, which is energetically unfavorable f or compounds with small, strongly electronegative anions. The combinat ion of two factors has been identified to be responsible for the struc tural differences between these compounds. The first is the electroneg ativity difference between the two types of atoms that form the solid: for strongly electronegative non-metal atoms like O or F the ReO3-typ e structure is expected to be the most stable, while for the combinati on of less electronegative atoms like the pnictides with late transiti on metals the skutterudite structure is preferred. The second factor i s the relative size of the constituting atoms: small atoms like F and O favor the ReO, structure, while larger atoms like P and As stabilize the skutterudite one.