Charge-density-wave instability in TlMo₆O₁₇, a new quasi-two-dimensional purple bronze

Single crystals of TlMo₆O₁₇ purple bronze have been grown using a temperature gradient flux technique. TlMo₆O₁₇ is trigonal with space group P3 or P3 and a = 5.543(2) A ̊, c = 14.000(2) and appears to be isostructural with K_0.9Mo₆O₁₇. The transport properties of TlMo₆O₁₇ are similar to that of K_0.9Mo₆O₁₇. The temperature dependence of the resistivity shows a metal-metal transition at ∼113K, probably associated with a charge-density-wave driven phase transition. The magnetic susceptibility decreases sharply near the temperature of the anomaly seen in the resistivity. The electronic properties of the quasi 2D purple bronzes, A_0.9Mo₆O₁₇ with A = Li, Na, K, Tl are compared. It is shown that despite the similarity of the basic Mo₆O₁₇ network structure in all, the properties vary substantially with the A cations. In contrast, the quasi 1D blue bronzes, A_0.3MoO₃ with A = K, Rb, Tl have nearly identical transport properties.