General Voltage-Step Responses and Impedances of Mixed-Conductor Films and Diodes: Metal-Conduct Cells with Mobile Anions or Cations.

摘要

Time-dependent equations for coupled electron hopping and anion or cation displacement in thick, electroneutral films are nonlinear. For plane sheet solutions of an electron/anion mixed conductor (Os(II/III)ClO4(-)) and an electron/cation mixed conductor (Ir(II/III)H+ or -M+ oxide), the Boltzmann transformation is only applicable at short times. The general problem is treated by reducing the equation to classical form and investigating the concentration dependence of the coupled D and both t sub e and t(anion or cation). Local micro fields cause coupling of mobilities and generation of space charge in a classical way. Current-time responses to voltage steps are characterized by three time constants: an Ohmic period, a theta function (generalized Cottrell) period, and a steady state. The steady current is independent of counterion mobility in this model. Swelling (uptake of water) and Donnan exclusion failure (uptake of whole salts) are excluded. Exact small amplitude impedance functions show two characteristic time constants: bulk and Warburg. Passage of dc current polarizes the charge-carrier concentrations and so increases both the real ac and dc resistances in a predictable way. Reprints. (rh)