COOLING RATE DEPENDENCE OF THE LATTICE-PARAMETERS OF (TMTSF)(2)CLO4

We report a diffractometric determination of the thermal dependence of the triclinic lattice parameters of (TMTSF)(2)ClO4. Low temperature m easurements show that c and gamma differ significantly in the quenched (Q) and relaxed (R) states. Tight binding calculations of the band st ructure of the organic sublattice, neglecting the ClO4- potential, sho w that the variations of gamma between the Q and R states do not affec t appreciably the shape of the Fermi surface (FS). We thus propose tha t the nesting properties of the FS are destroyed below the anion order ing transition by the b/2 component of the ClO4- Coulomb potential.