13C NMR study of the chemical pressure effect in (TMTTF)2[(AsF6)x (SbF6)1-x] (x 0.5)

13C NMR measurements of (TMTTF)2[(AsF6)x (SbF6)1-x] (x ∼ 0.5) alloy were performed in order to understand the chemical pressure effect and the electronic state at low temperatures. The charge-ordering transition temperature is the intermediate value between those of SbF6 and AsF6 salts. The broadening of NMR spectra and the weak temperature dependence of the spin-lattice relaxation rate at low temperatures indicate that this salt is situated in the vicinity of the phase boundary between the spin-Peierls and antiferromagnetic phases.