Effects of disorder on the transport properties ofbis(tetrathiatetracene)triiodide

Bis(tetrathiatetracene)triiodide [(TTT)₂{I}₃$] is a quasi-one-dimensional organic metal consisting of segregated stacks of tetrathiatetracene (TTT) cation radicals and polyiodide chains. The TTT and iodine (I) sublattices are incommensurate with respect to each other, and the iodine lattice exhibits considerable disorder. In this paper, we report measurements of the conductivity and thermoelectric power of single crystals of TTT₂{I}₃$ in which the degree of disorder is varied. The disorder is modified by crystallization processes and is characterized by x-ray studies. ${(TTT)}₂I₃ exhibits metallic behavior at high temperatures (100^∘K<T<300^∘K) even in the presence of considerable disorder. Below 100^∘{}K, (TTT)₂{I}₃$ undergoes a broad metal-nonmetal transition. The effects of disorder on this transition and on the low-temperature transport properties are discussed. The present results are compared with data on ${(TTT)}₂I₃ taken by other investigators.