Structural study of neutral-ionic transition in DMTTF-CA

Crystallographic investigation of temperature-induced phase transition of the tetrathiafulvalene-p-bromanil, TTF-BA charge transfer complex

“…9͒ or DMTTF-CA. 14 However, in these latter complexes the direction of the maximal variation corresponds to the stacking axis, contrary to TTF-BA where the shrinkage is stronger along the c axis ͑i.e., almost orthogonal to the stacking axes͒. Moreover, the transition is clearly marked for the gamma parameter: On decreasing the temperature, gamma increases linearly until the transition; below T c , gamma is almost temperature independent.…”

Structural evidence of ferrielectric neutral-ionic layered ordering in 2,6-dimethyltetrathiafulvalene-p-chloranil

“…The cryogenic equipment allowed a temperature stability of Ϯ0.1 K. To allow a direct comparison between DMTTF-CA and the prototype compound TTF-CA, we use the crystallographic conventional triclinic unit cell with a as the shortest lattice vector and c the longest one, leading to a as the stacking axis, like in TTF-CA, instead of c as in previous publications. 7,15,16 …”

“…Contrary to TTF-CA, there was no abrupt jump of the cell parameters observed at the transition; the cell parameters at 40 K reflected a nearly linear contraction with temperature. 16 Standard reflections, indexed (2 10), ͑0 0 1͒, and (1 14) in the high-temperature reciprocal lattice, were used at all temperatures; they were measured every 180 min to check the stability of the instrument and crystal. Absorption and Lorentz factor corrections were carried out.…”

“…7 However, the direct evidence of staging superstructures requires the use of diffraction techniques. For DMTTF-CA, a first structural study 16 has shown anomalies in the temperature evolution of lattice parameters and in the average structure through the transition ͑the authors indicated a possible masking of superlattice reflections by /2 contamination͒. The present paper reports on the observation in DMTTF-CA of superstructure reflections characteristic of a cell doubling and on the direct structural evidence of long-range ordering comprising both N-I layering and dimerization by using high-resolution x-ray diffraction.…”

Effect of chemical doping on the ferroelectric neutral-ionic phase transition in tetrathiafulvalene-p-chloranil(TTF−QClHoriuchi1, Kumai2, Okimoto3 et al. 1999Phys. Rev. B191110View full textAdd to dashboardCite

“…11 Ferroelectric molecular arrangement is also observed for the 4,4Ј-dimethyltetrathiafulvalene-QCl 4 complex in the ionic phase at low temperature. 12 The NI transition can be thus regarded as a unique phenomenon showing such ferroelectricity as realized by both the valence and spin-Peierlslike instabilities. Incidentally, another anomalous dielectric response emerges in the neutral phase of TTF-QCl 4 due to the dynamics of the charged defects perhaps arising from the thermally excited ionic domains.…”