Phase control of neutral-ionic states by chemical doping

The effect of molecular substitution on the neutral-ionic (NI) phase transition has been investigated for TTF-p-chloranil (QCl4) by the measurements of dielectric constant. Due to the ferroelectric nature in the transformed ionic state, the dielectric constant shows a large anomaly at the NI transition temperature, which was remarkably but continuously lowered down to zero temperature by the molecular substitution. X-ray structural analysis revealed the large “chemical pressure” effect for TSF doped crystals.