Charge localization in organic conductors (TM)_2X: The influence of anion ordering

An investigation of the different contributions leading to charge localization in a 1/2 or 1/4 filled band 1D conductor has been conducted through a study of transport properties in the solid solution [(TMTSF)_(1-x)(TMTTF)_x]_2ReO_4. The existence of an ordering transition of the anions allows to identify two contributions to the electronic potential with wave vector 4k_F. A dominant on-site 4k_F potential besides the bond contribution is revealed when Umklapp scattering is pertinent via the weakening of the localization arising at the (0, 1/2, 1/2) anion ordering which is stabilized under pressure in the compound [(TMTSF)_0.5(TMTTF)_0.5]_2ReO_4 at variance with the enhancement of localization observed in the homomolecular (TMTTF)_2ReO_4 material.