Cooling rate dependence of the lattice parameters of (TMTSF)/sub 2/ClO/sub 4/

Summary form only given. The quasi-one-dimensional conductor (TMTSF)/sub 2/CIO/sub 4/ exhibits a ground state whose nature depends upon the cooling rate of the sample in the vinicity of the 24 K anion ordering transition. Relaxed (R) samples are superconductor with a T/sub c/ /spl ap/ 1.2 K, while quenched (Q) samples exhibit a spin density wave (SDW) ground state below about 6 K. Although it has been previously established that the fraction and size of ordered domains of C10/sub 4//sup -/ depend strongly on the cooling rate [1], the interplay between structural and electronic degrees of freedom is not clearly understood. In that purpose we present a diffractometric determination of the triclinic lattice parameters between 13 and 300 K. Our results agree with those previously reported by B.Gallois et al. [2]. However the better resolution reveals anomalies below 50 K in the thermal dependence of these parameters which could be related to the freezing of the CH/sub 3/ groups of the TMTSF molecule. We have also performed low temperature measurements of the triclinic lattice parameters in R and Q samples, cooled respectively at 2K/h and 30K/min around 24 K, and found significant differences for the c (CR-cQ/c = - 0.2% ) and Y (YR-YQ/Y = + 0.3%) lattice parameters. The c parameter controls the coupling between (a,b) conducting planes, while the Y angle controls the balance between interchain transfer integrals within these planes. The relative variation of these parameters amounts to that observed[3] in (TMTSF)/sub 2/PF/sub/6 pressurized by several Kbars at low temperature.