Hopping Conducitivity Studies On Disordered Systems

Based on the disadvantage of the former electronic conductance theory applied on the disordered system, and considering the interaction between the phonon> electric field and electron, a EPF (Electron-Phonon-Field) conductance model of electronic tunnel transfer is set up, and new D.C and A.C conductance formulas in one-dimensional disordered system are derived. By calculating the D.C and A.C conductivity, the conductance characteristic of disordered system is analyzed systematically and the effects of some parameters, such as disordered degree, temperature, electric field and atom number, on the D.C and A.C conductance are discussed in detail. The result shows that the disordered system appears the characteristic of negative differential dependence of resistance and temperature in low temperature region, i.e. the conductivity increases with the raising of temperature, however decreases with the raising of temperature in high temperature region. The temperature according to the maximum value of conductivity is different from different systems. The D.C conductivity varies with changing the electric field and has peaks or sidesteps due to the resonant electronic tunnel transfer. It doesn't coincide with the regular pattern of ohm law. The A.C conductivity linearly increases with the raising of frequency of electric field. The slopes of conductivity vs frequency curves are different according to different systems. The disordered degree has obvious influence on the conductance. When the voltage or frequency of electric field is not so high, in low temperature region the conductivity is greater when the disordered degree is weaker. In high temperature region, when the disordered degree is not so great, its suitable rising is advantageous to form the resonance of electronic tunnel transfer and increase the conductivity of the system. However when the disordered degree is great overly, the conductivity is to become little with the raising of disordered degree. The number of atoms is also an important factor that influences the conductance of disordered system. According to the D.C conductance, when the electric field is constant, the conductive curves of different disordered system have one intersection. The system with more atoms has greater D.C conductivity under the temperature according to the intersection and the case is contrary above that temperature. When the temperature is constant, the conductivity of the system with more atoms is obviously greater than the one with less atoms in the high voltage region, nevertheless, their conductivity varies little in the low voltage region; According to the A.C conductance, when the frequency of electric field is constant, the relationship between A.C conductivity and atom number is similar with that of D.C conductivity. When the temperature is constant, the slopes of conductivity vs frequency curves varies with different systems that have different atoms. The less atom number, the larger curve slope.As the application of the electronic hopping conductance theory in the disordered system, we study the conductance characteristic of nanometer system that hasn't periodic structure. A model of one-dimensional random nanometer chain is set up.Two parameters, the crystalline grain size S and the distortion of interfacial atoms D are selected and their effects on the conductance are analyzed systematically. The nanometer system appears the characteristic of negative differential dependence of resistance and temperature in low temperature region. The D.C conductivity varies with changing the electric field and the A.C conductivity linearly increases with the raising of frequency of electric field. The crystalline grain size and the distortion of interfacial atoms have great influence on the D.C conductance of the nanometer system. Its conductivity decreases with cutting down the crystalline grain size and enhancing the distortion of interfacial atoms.