Chalcogenides of rare earth elements having an intermediate valence

The valence state of Re in chalcogenides having the structural type NaCl and Th/sub 3/P/sub 4/ has been estimated on the basis of an analysis of the geometrical dimensions of the unit cells and certain physical properties. A comparison of the electrical resistance in the series tellurides-selenides-sulfides revealed that rho varies from 10 to 10/sup 4/ and 10/sup 7/ Omega x cm, respectively. Such an appreciable divergence can probably be explained by the metallization of the chemical bond on passing from the sulfides to selenides and tellurides.