Electrical properties and phase transitions of TlCu3S2 and BaCu2S2

TlCu3-xS2 showed a phase transition at similar to 100 K, which is character ized by ajump of the resistivity and a steep increase of the Hall coefficie nt on cooling. The dominant carriers were observed to be holes in the measu rements of Seebeck coefficients (S) and Hall coefficients (R-H). The holes were found to originate mainly from copper vacancies. The Hall mobility sca rcely changed at the transition temperature, alpha -BaCu2-xS2 showed semico nductive behaviors with fairly large values of S, and exhibited a phase tra nsition at similar to 200 K. beta -BaCu2-xS2 was a semiconductor, exhibitin g a phase transition at ca. 250 K. S and R-H measurements showed that the d ominant carriers beta -BaCu2-xS2 was a semiconductor, exhibiting a phase tr ansition at ca. 250 K. S and R-H measurements showed that the dominant carr iers are holes in both alpha and beta phases. (C) 2001 Elsevier Science B.V . All rights reserved.