Raman Spectroscopy Evidence Of Domain Walls In The Organic Electronic Ferroelectrics (Tmttf)(2)X (X = Sbf6,Asf6,Pf6)

Charge ordering in the quasi-one-dimensional organic conductors (TMTTF)(2)X (X = SbF6, AsF6, PF6) was studied by using Raman spectroscopy. In the charge-ordered phase three vibrational features related to the ring breathing mode nu(10)(a(g)) of neutral (TMTTF0) and ionized (TMTTF+0.5 and TMTTF+1) are observed at about 503, 507, and 526 cm(-1), respectively. The bands of donor molecules with charge +0.5e are assigned to ferroelectric domains while the bands of neutral and fully ionized molecules to domain walls. The shape of the band at about 526 cm(-1), attributed to the charged domain walls (molecules with charge + 1e), reveals important differences between salts, i. e., indicates the presence of relaxor ferroelectricity which is well seen in (TMTTF)(2)PF6.