Optical reflectivity spectra of the mixed-stack organic charge-transfer crystal tetrathiafulvalene-p-chloranil under hydrostatic pressure

Publisher Website
Google Scholar
Abstract
Optical reflectivity spectra and electric conductivity have been measured on single crystals of tetrathiafulvalene (TTF)-p-chloranil under hydrostatic pressure up to 11 kbar at room temperature. From their characteristic behavior under pressure, it is concluded that TTF-p-chloranil crystals undergo a gradual pressure-induced neutral-to-ionic (N-I) transition in an intermediate region from 0 to about 10 kbar, in contrast with a first-order temperature-induced N-I transition. In this pressure range, both quasineutral and quasi-ionic molecular domains coexist in the lattice, until a discontinuous transition to a dimerized ionic phase occurs at about 11 kbar. It is suggested that the dynamical behavior of N-I domain walls is responsible for a pressure-induced exponential increase of the electric conductivity.