The charge and energy transport in some highly conducting quasi-one-dimensional organic crystals is studied. Two electron-phonon interactions and scattering on impurity are considered. It is found that the Wiedemann-Franz law is strongly violated. The Lorentz number is diminished for a large interval of Fermi energy: ͑1͒ due to faster decrease in thermal conductivity than the electrical conductivity when the conduction band width is decreased, and ͑2͒ due to strong dependence of relaxation time on carrier energy. The Lorentz number becomes dependent on crystal purity and may be reduced by up to ten times and even more in comparison with ordinary materials. This is favorable for the increase of thermoelectric figure of merit ZT. It is predicted that in really existing crystals of tetrathiotetracene-iodide, when after the optimization of carrier concentration ZT = 1.4 is expected, the Lorentz number is reduced by 1.6 times with respect to the usual value.
A systematic theoretical analysis of electronic states and thermoelectric transport in PbTe/Pb 1Ϫx Eu x Te quantum well structures is presented, employing more realistic well model than has been used up to now. The carrier scattering both on optical and acoustical phonons is considered. The kinetic equations are solved using the variational method and taking into account the intersubband transitions. The electrical conductivity, thermopower ͑Seebeck coefficient͒ and thermoelectric power factor as functions of the well width are studied for quantum well ͑QW͒ structures with ͑100͒ and ͑111͒ crystallographic orientations and different carrier densities. It is found that the power factor is greater in ͑100͒ QW's, but the more realistic the well model is the lower the power factor. The dependencies of the power factor on the carrier density are determined and analyzed. It is shown that when the potential barrier height grows but the carrier density remains constant, the power factor is decreased. However the latter may be increased by increasing the permissible carrier density. So the expected values of the power factor for QW's with Uϭ250 meV, dϭ20 Å , and nϭ5ϫ10 19 cm Ϫ3 are 175 W cm Ϫ1 K Ϫ2 in the case of ͑100͒ orientation and 108 Wcm Ϫ1 K Ϫ2 for the ͑111͒ one. The comparison with the results of recent experiments is also presented.
cel Mare av. 168, Chisinau, Rep. of Moldova A more complete physical model for nanostructured crystals of tetrathiotetracene-iodide that takes into account the interaction of carriers with the neighboring one-dimensional (1D) conductive chains and also the scattering on impurities and defects is presented. For simplicity the 2D approximation is applied. It is shown that this model describes very well the temperature dependencies of electrical conductivity in the temperature interval between 180 and 300 K and of Seebeck coefficient between 50 and 300 K, the highest temperature for which the measurements were reported. For lower temperatures it is needed to also consider the fluctuations of dielectric phase which appear before the metal-dielectric transition. It is found that the predictions made in 1D approximation are valid, if the crystal purity is not very high, the electrical conductivity is limited up to ~ 3.5106 -1 m -1 and the thermoelectric figure of merit up to ZT ~ 4.
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