Diffusion with rearranging traps

A model for diffusion on a cubic lattice with a random distribution of traps is developed. The traps are redistributed at certain time intervals. Such models are useful for describing systems showing dynamic disorder, such as ion-conducting polymers. In the present model the traps are infinite, unlike an earlier version with finite traps, this model has a percolation threshold. For the infinite trap version a simple analytical calculation is possible and the results agree qualitatively with simulation.Comment: Latex, five figure

Effective medium theory for ionic conductivity in polycrystalline solid electrolytes

It is usually found that for the relatively poor ion conducting solids, the ionic conductivity for the pure polycrystalline sample is higher than that of the single crystal. The difference has been suggested to be due to the presence of dislocations grain boundaries etc. in the polycrystal. In this paper we propose a theoretical model for the polycrystal including these defects. A quantitative estimate of the grain boundary contribution to conductivity is made using an effective medium theory and it is found to exhibit an Arrhenius behaviour. The results for calcium fluoride, thallium chloride and cuprous chloride show that the grain boundary conductivity is ≈ 105 times that of the single crystal. The ratio of activation energy for grain boundary conduction to that of the single crystal is found to be 0.5–0.6 which is consistent with results obtained from other sources

Growth of New Form of Polycrystalline Silicon Thin Films Synthesized by Hot Wire Chemical Vapor Deposition

In this work, we report on next-generation hot wire chemical vapor deposition technique, we call it ceramics hot-wire CVD. Using a new concept of rectangular ceramics filament holder and confinement of thermal radiation from the filament , a new form of polycrystalline silicon thin films has been developed at low temperature (˜ 250°C). The grains are found to be symmetrically distributed in array along the parallel lines, in (111) direction. On the surface of individual grains, five-fold and six-fold symmetries have been observed and we suspect that we developed buckyball type giant silicon molecular solids with different crystalline silicon lattice other than standard single-crystal silicon structure. We observed rarely found icosaderal symmetry in silicon thin films. This hypothesis has been supported by multiple Raman active transverse optical modes and the crystallographic structure analyzed by X-ray diffraction

Low band gap amorphous silicon deposited under He dilution in the γ regime of an rf glow discharge: properties and stability

A new type of hydrogenated amorphous silicon film having variable bandgap (1.7-1.5 eV) has been developed in an rf powered plasma enhanced chemical vapor deposition system using a mixture of silane and helium at a subtrate temperature of 210°C. The deposition conditions were chosen so that the rf glow discharge occurs in the γ regime, usually avoided because of powder formation. The influence of the chamber pressure, on the optical gap, the hydrogen content and the electronic properties is presented. Increasing the pressure up to 1.8 Torr is found to decrease the optical gap down to 1.5 eV. The densities of states of these films were measured by electron spin resonance, constant and modulated photocurrent techniques. The density of states above the Fermi level is found to be two orders of magnitude less than that of standard amorphous silicon. Moreover, unusually fast kinetics of degradation are observed. This new material could be a good alternative to amorphous silicon germanium alloys

Ion-conductivity and Young's modulus of the polymer electrolyte PEO-ammonium perchlorate

We present a study of impedance spectroscopy (IS) under varying loads. An equivalent circuit is proposed taking the deformability and the effect of change in free volume into account, which yields the dc ion-conductivity as well as the Young's modulus from these results. Independent measurements of elastic properties are done and the result is compared with Young's modulus predicted from IS. The sample we studied is PEO-NH4ClO4 with a salt fraction of 0.19 by weight, with frequencies varying in the range of 40 Hz to 3 MHz and loads varying from 400 to 1600 g