ELECTRICAL-PROPERTIES AND PHASE-TRANSITIONS IN SUPERCONDUCTING QUASI-ONE-DIMENSIONAL CHALCOGENIDES INXNB3X4 (X = S, SE, AND TE)

Electrical properties and phase transitions were investigated in the quasi-one-dimensional ternary chalcogenides InxNb3X4 (X = S, Se, and Te; x = 0.5 for X = S, and 1.0 for X = Se and Te), with results indicating that the InrNb3Te4 system has two new kinds of phase transitions. Based on the values of the transition temperatures Tt, this system is classified into two groups, i.e., Group 1 samples with 0 ≤ x < 0.55 having T1 = ≈40 and ≈80 K, and Group 2 samples with 0.55 < x ≤ 1.0 having Tt = ≈50 and = 140 K. Electron diffraction measurements showed the 140-K transition to be associated with a charge-density-wave (CDW) formation accompanied by the appearance of a superstructure that can be explained by the commensurate wave vectors q = ±(1 3a* + 1 3b* + 1 9c*, which are slightly larger in the c* component as compared with those previously observed in Nb3Te4 of q = ±(1 3a* + 1 3b* + 3 7c* . The increase in the c* component was interpreted as being caused by the increase in Fermi energy due to In insertion. Thermopower measurements on InxNb3Te4 showed the dominant carriers to be holes. In addition, the InxNb3Se3.84 system (0.40 ≤ x ≤ 1.0) showed a new CDW-like transition at ≈30 K. The superconducting critical temperature Tc of InxNb3X4 was increased by several degrees when the in content x was increased above 0.5. © 1993 Academic Press, Inc.