Heat Pulse Diffusion in TEA(TCNQ)₂

Abstract

Measurements of the thermal diffusivity D on crystals of the highly anisotropic organic semiconductor TEA(TCNQ)? are reported. These measurements are made using a heat pulse method. For the crystal axis 1 parallel to the TCNQ columns and associated with the largest component a, of the electrical conductivity, D, is 1.6 x om2 8-l a t 200 R. The thermal conductivity k, is evaluated to 4 mW cm-' K-I a t 300 K with an estimated electronic contribution of only 1%. The phonon mean free path at 300K is extremely small I, e 2 A, of the order of the shortest distance between the TCNQ molecules in a column. It is thus expcctcd to be almost constant a t this temperature, a result, which is also suggested from the observed T dependence of D,.

Thermal diffusivities of functionalized pentacene semiconductors

“…Using c = 1.48 J/gK and density ρ = 1.1 g/cm 3 [7], we find  long = 16 ± 2 mW/cm·K. This value of  long is several times larger than the room temperature value for rubrene [5], but comparable to the phonon thermal conductivity of quasi-one dimensional organic conductors containing segregated molecular stacks with excellent -orbital overlap [21][22][23]. In fact, its value suggests that, in addition to acoustic phonons, a significant fraction of the heat is carried by low energy, propagating optical phonons.…”

“…In summary, we have measured the longitudinal (needle-axis) and transverse, interlayer thermal conductivities of crystals of TIPS-Pn by ac-calorimetry. We have found that the longitudinal value is higher than that of rubrene [5] and pentacene [26] and comparable to quasione dimensional conductors with excellent -orbital overlap [21][22][23]. The transverse thermal diffusivity is at least an order of magnitude larger than the longitudinal.…”

Infrared Studies of TEA(TCNQ)2 Crystals Damaged by Electron Irradiation and Mechanical Treatment

“…The DSC measurements have shown a first-order phase transition at 220 K attributed to the TEA disorder [3]. NMR results [4] together with electric conductivity [5], thermopower [6], thermal conductivity [7], and infrared spectra [8] confirm the mechanism of the phase transition.…”

Temperature Study of the Polarized Reflectivity of TEA(TCNQ)2Single Crystal

“…NMR results for TEA(TCNQ)2 [17] confirm that the twofold disorder of the cation is static below 200 to 220 K and increasingly dynamic in nature as room temperature is approached. We point out that together with d.c. conductivity and DSC anomalies, presumptions of a phase transition at 220 K were observed previously in experimental results such as: the thermopower [20], the a.c. conductivity [21] and the thermal conductivity measurements [22].…”