Phase transitions in quasi-one-dimensional chalcogenides of BaNbxS3 and BaTaxSe3

BaNbS3 phase was found to be stable in the composition range between x=0.85 and 0.97 for BaNbxS3. The conduction nature was varied from semiconductive to metallic with increasing Nb content. Semiconductor-to-metal (S–M) transition was observed at ∼170 and ∼250 K in BaNb0.95S3 and BaNb0.97S3, respectively. BaTaSe3 phase was stable in the range between x=0.90 and 0.95 for BaTaxSe3. BaTaxSe3 with x=0.90 and 0.95 showed a semiconductor-to-semiconductor transition at ∼140 K, which is characterized by a large jump of the resistivity from ∼106 to ∼1012 Ω cm. Seebeck measurements showed electron conduction in both BaNbxS3 and BaTaxSe3.