Study at 10⁸ and 2 × 10⁸ Hz of the Electrical Conductivity and Dielectric Constant of the Highly Anisotropic Organic Semiconductor TEA (TCNQ)₂

Abstract

The ac electrical conductivity and anisotropy, including an evaluation of the dielectric constant, a t 108 and 2 x 108 Hz in the range 77 to 350 O K is investigated. A hopping mechanism is evidenced from the dispersion of conductivity observed below 200 OK, and is associated with the existence of tails of localized states a t the edges of a band gap. The vanishing dispersion in the upper temperature range is likely to indicate that an interband transition process may then become important for conduction.Nous pr6sentons une etude de la conductivit6 Blectrique et de son anisotropie, comprenant aussi une 6valuation de la constante dielectrique, & lo8 e t 2 x lo8 Hz entre 77 e t 350 OK.La dispersion de la conductivit6, observee au dessous de 200 OK, met en Bvidence un processus de conduction par sauts qui peut btre attribu6 8. l'existence de ,,queues" #&tats localises aux extrBmit6s de la bande interdite du semiconducteur. L'absence de dispersion des temperatures superieures pourrait indiquer qu'un processus de transitions bande 8. bande devient alors predominant vis 8. vis de la conduction.

Polarized Optical Reflection Spectra of the Highly Anisotropic Organic Semiconductor TEA(TCNQ)2

“…The assumption seems plausible that t.his unexpected anisotropy is caused somehow by a coupling of the phonons to the highly anisotropic electron syst,em. and a a t the low-frequency end of the spectrum as measured along t)he direct,ion of TCNQ chains, with data obtained elsewhere in dc field [7], at, lo8 and 2 x lo8 Hz [20] and (by Shchegolcv) a t 1Olo Hz [l]. The conduct,ivity values for the various frequencies result in a reasonably smooth curve which rcmains constant between dc and x 1011 Hz…”

Dipolar glass and magneto-electric coupling within a π-stacked organic system

“…Within the loss, the behaviour at high frequencies (T 4 240 K) is likely due to the sample being semiconducting or metallic above this cation freezing transition. As an estimate to gain the magnitude of the dielectric constant, 23,24 the crystal dimensions could be approximated as 3 Â 0.5 Â 0.2 mm in length. This results in a permittivity of 2.4 Â 10 3 , if one assumes a capacitance of 0.7 pF, which is a fairly large value but is in agreement with what is expected for a ferroelectric, although an order of magnitude lower than that of a colossal permittivity material.…”

Order‐Disorder Phase Transition in TEA+(TCNQ)2‐

“…Purthermore, we would point out that together with dc conductivity and DSC (ii) the ac conductivity at 100 and 200 MHz [13] where for ax, a , , and a, there appears a noticeable deviation with frequency below 200 K ; (iii) the amplitude of the signal observed on probes positioned along a crystal needle of TEAoTCNQ, in the thermal conductivity measurements by a heat pulse method [14]. The data which are concerned with both heat capacity and thermopower show a n increase at x 210 K (Pig.…”