Magnetic susceptibility, electrical resistivity, and thermoelectric power measurements ofbis(tetrathiotetracene)-triiodide

The magnetic susceptibility (χ), electrical resistivity (ρ), and thermoelectric power (S) of bis(tetrathiotetracene)-triiodide were measured for $9 100$ K, and (ii) thermopower S=S₀T+S₁T where S₀=1124 {μ}V and S₁=1.07×10^-1 {μ}V/K². The magnetic susceptibility, corrected for 0.25% spin-{} impurities, is + 2.2 ×{} 10^-4 emu/mol at room temperature. The term in the thermopower data linear in temperature is interpreted using a one-dimensional tight-binding model to yield a value for the transfer integral (t) of 0.16 eV. The high-temperature value of χ is enhanced by Coulomb correlations. Using the antiferromagnetic Heisenberg-chain model appropriate to this limit we find that the on-site electron-electron repulsion (U) is {~} 2.0 eV. Phase transitions have been found at 50 K in χ and at 21 K in dlnρdT. The conductivity of TTT-(I₃)0.5 remains large at low temperatures [ρ(10 K)~5×10^-3 {Ω}cm], and the magnetic susceptibility, corrected for spin-{} impurities has a large paramagnetic value (1.2 ×{} 10^-4 emu/mol) at low temperature ($T<20$ K).