ja0016654_si_001.pdf (324.5 kB)
Ferroelectric Valence Transition and Phase Diagram of a Series of Charge-Transfer Complexes of 4,4‘-Dimethyltetrathiafulvalene and Tetrahalo-p-benzoquinones
journal contribution
posted on 2001-01-05, 00:00 authored by Sachio Horiuchi, Yoichi Okimoto, Reiji Kumai, Yoshinori TokuraVariation of the ferroelectric phase transition has been investigated for a series of isomorphous
donor (D)−acceptor (A) charge-transfer complexes composed of 4,4‘-dimethyltetrathiafulvalene (DMTTF) and
tetrahalo-p-benzoquinones by measurements of dielectric susceptibility, X-ray diffraction, and infrared molecular
vibrational spectra. The neutral−ionic phase transition of DMTTF−p-chloranil at 65 K accompanies a dielectric
peak anomaly associated with the DA stack dimerization. Successive halogen replacement by bromine in the
component tetrahalo-p-benzoquinone molecule expands the lattice along the DA stack of the DMTTF complex,
and reduces the critical temperature steeply toward zero temperature in an analogous way to the critical behavior
of quantum ferroelectrics. The 2,6-dibromo-substituted compound showing the behavior of the quantum
paraelectricity is located in the immediate vicinity of the quantum critical point of this phase diagram as
signified also by enhancement of the ionicity, the dielectric susceptibility, and the dynamical dimeric distortion
at the lowest temperature.