Effect of chemical doping on the ferroelectric neutral-ionic phase transition in tetrathiafulvalene-p-chloranil(TTF−QCl

Abstract

Effects of molecular substitution on the neutral-ionic ͑NI͒ phase transition have been investigated for tetrathiafulvalene ͑TTF͒-p-chloranil (QCl 4 ) complex doped with tetraselenafulvalene ͑TSF͒ or trichloro-pbenzoquinone (QCl 3 ) molecules. Except for the fully substituted compound TTF-QCl 3 of minor structural modifications, x-ray-diffraction measurements confirm the isostructurality over a wide compositional range as well as smooth change in the lattice constants by molecular replacement. With increasing TSF concentration, the peak in the dielectric constant corresponding to the ferroelectric NI transition smoothly shifts toward zero temperature due to the lattice expansion. Around the critical concentration are found some characteristics of quantum ferro͑para͒electricity. Although the increment of QCl 3 concentration also lowers the peak temperature of the dielectric constant, the dielectric anomalies reveal glasslike frequency dependence. We attributed the glasslike behavior to the strong ''pinning-impurity'' effect of QCl 3 which yields binary-phase separation into ferroelectric ͑ionic͒ and paraelectric ͑neutral͒ regions. ͓S0163-1829͑99͒03617-6͔

Chemical approach to neutral–ionic valence instability, quantum phase transition, and relaxor ferroelectricity in organic charge-transfer complexes

“…13) due to destabilization of the I state by the impurities [74]. Below the critical concentration, y c % 0.11, the dielectric peak remains sharp and characteristic of the typical ferroelectrics.…”

Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions

“…The dielectric data of Horiuchi et al are taken as a function of temperature at ambient pressure, [6][7][8][9][10] or, more recently, as a function of pressure, up to ϳ10 kbar, at constant temperature. 11 Decreasing volume on cooling or compression stabilizes the ionic phase by increasing the crystal's Madelung energy.…”

“…Horiuchi and co-workers [6][7][8][9][10][11] have recently studied NIT's in a series of substituted TTF's and CA's whose static dielectric responses have large peaks (Ͼ100). Their interpretation is a quantum phase transition between a neutral-regular and an ionicdimerized GS controlled by an external parameter such as temperature or pressure.…”

Variation of Excitation Spectra in Mixed-Stack Charge-Transfer Complexes

“…E-mail: kxy@ims.ac.jp ionic phase appears between the two (Leme´e-Cailleau et al, 1997). Indeed, the dielectric constant shows very large enhancement around the transition (Okamoto et al, 1991;Horiuchi et al, 1999). Theoretically, the neutral-ionic phase transitions have been studied by using quantum Monte Carlo method (Nagaosa, 1986), the exact diagonalization method (Girlando and Painelli, 1986;Painelli and Girlando, 1988;Anusooya-Pati et al, 2001), the finite-temperature density-matrix renormalization-group method (Yonemitsu, 2001), and so on.…”

“…The irradiation of lights causes nucleation of metastable domains. Theoretically, the adiabatic potential is calculated for a pair of a kink and an anti-kink connecting the neutral phase with the ionic phase (Huai et al, 2000). The photo-induced phase transition is viewed as a domino effect and characterized by a threshold field for the transition .…”