Electrical properties of mixed valence rare earth sulfides (Smsub(1-x)Gdsub(x))3S4

A new type of the valence transition was found in the mixed valence rare earth sulfides, (Smsub(1-x)Gdsub(x))3S4. The conductivity of the materials gradually decreased up to x = 0.80 with increasing Gd concentration, in spite of mixing the metallic Gd3S4 with the semiconducting Sm3S4. A drastic change from the semiconducting to metallic conduction, however, was observed at the range between x = 0.80 and x = 0.85. These phenomena were explained by the valence change of the samarium ion in the solid solution. (author)