TMTSF TCNQ

XRD patterns of TTF-TCNQ hlms grown by CVD on Si(lOO) substrates also show this kind of extra reflections (de Caro et al, 2000a). This is perhaps the first evidence, albeit incomplete and thus questionable, of a new crystallographic phase of TTF-TCNQ. The conclusive observation of a new phase of TTF-TCNQ, e.g., with mixed-stacked structure as for the red phase of TMTSF-TCNQ, would be extremely interesting. The known and newly observed structures for both TMTTF and TTF-TCNQ might be tentatively ascribed to the thermodynamical and kinematical phases, respectively. 

TMTSF-TCNQ (24), TSF-Et2TCNQ (25) BEDT-TTF(ET)-TCNQ(26) —> FT two-dimensional [Pg.74]

TCNQ salts are practically indistinguishable. Hence, TMTSF-TCNQ and... 

FIGURE 9 Real and apparent conductivities of TMTSF-TCNQ. Solid line d.c. 

The most recent work has dealt with modifications of the donor in the prototype TTF-TCNQ /l/, including the notable successes TMTTF-TCNQ /2/, TSF-TCNQ /3/, TMTSF-TCNQ /4/ and HMTSF-TCNQ /5/. 

TMTSF-DMTCNQ deserves comparison with the conducting form of the paren. t system TMTSF-TCNQ /4/. The temperature dependences of the conductivities of both systems are very alike, but in TMTSF-TCNQ the maximum is situated at 71 K. 

Q- TTF-TCNQ (above 58 K) TMTSF-TCNQ (black form) NMP-TCNQ TSF-TCNQ (above 40 K) HMTSF-TNAP TMTTF-TCNQ HMTTF-TCNQ... 

For small or intermediate U (as in TTF-TCNQ) one can see extra Bragg reflections at both 2kp and also at 4kp, while for TMTSF-TCNQ (small U) only 2kp scattering is seen. For example, in TTF-TCNQ A. / d = 3.39 (the distortion is incommensurate with the original lattice), and Z = 0.59 is obtained. When the distortion is commensurate with the lattice (e.g. when Z is a rational fraction, 1/4, 1/3,1/2, 3/4, or 1), then it usually requires less energy than an incommensurate distortion, which occurs at a higher temperature. For TTF-TCNQ, the situation is more complex it is a two-chain material, and the bandwidth for the TTF chain is... 

Some of the early Hopkins conductivity data for the series TMTTF-TCNQ, TTF-TCNQ (for whom the conductivity anisotropy is 500 5 <1), TMTSF-TCNQ, and HMTSF-TCNQ are shown in Fig. 10 [25, 26, 112-115]. From other (mainly magnetic) data it is surmised that... 

Fig. 10. Temperature-dependent resistivities of TTF-TCNQ, TMTTF-TCNQ, TMTSF-TCNQ, and HMTSF-TCNQ [26].

An important consideration,in deciding what compounds to synthesise,in order to stabilise the superconducting state versus the CDW or SDW in molecular lattices, is the effective dimensionality. A first priority is to make the lattice less purely one-dimensional, so as to make it stable to Peierls distortion. In that context, the compound (HMTSF)(TCNQ) was a significant early example.HMTSF (hexa-methylene-tetraselenofulvalene) was synthesised to explore the consequence of introducing more bulky substitution of the TSF moieties,with the expectation that the system would be rendered more purely one-dimensional. Yet, it was found that, unlike TMTSF-TCNQ, which like TTF-TCNQ has a major metal-insulator transition near... 

Fig. 4. Temperature variation of resistance of (a) (TMTSF)(TCNQ) and (b) (HMTSF)(TCNQ).21...

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