Grain-electrode contact

Fig. 2.3. Schematic view of a porous nanocrystaUine sensing layer with a one-dimensional representation of the energetic conduction band. A inter-grain band bending, eVs, occms as a consequence of smTace phenomena, and a band bending, eVc, occurs at the grain-electrode contact. Eb denotes the minimmn conduction band energy in the bulk tin oxide, and Ep is the Fermi-energy in the electrode metal...

A first approximate approach for estimating N,pb, or /tpb.n is to use scanning electron microscopy to estimate the average grain size, d, of the electrode. One then assumes spherical grains for the electrode film and semispherical grains in contact with the solid electrolyte to obtain ... 

The fact that in the case of the bicrystal in Figure 54 the effective thickness calculated from the low-frequency semicircle is very much greater than expected from the width of the boundary, while the activation energy is almost equal to that of the bulk, points towards a frequently overlooked complication, namely to current-constriction effects. Such constriction effects occur287 when the crystal grains are not ideally sintered together, if pores or second phases are included, and interrupt the lateral conductivity of boundaries, as is the case for inhomogeneous electrode contacts. 

Other Effects Grain Size, Electrode Contacts, Fixed Charge at Interfaces. 103... 

Different gas interactions in porous layers. The gas penetrates into the layer and interaction can therefore take place at the grain-grain boundaries (a), the grain-AljOj substrate contact (b) and at the grain-electrode-AljOj substrate contact (c). 

Boundary impedances refer either to heterocontacts, such as the contacts of the electrode to the electrolyte or contacts between the grains of different phases in composites, or to homocontacts, i.e., grain boundaries. In this chapter, we restrict ourselves to resistive... 

Rgb, c grain boundary resistance between two large contact electrodes... 

Fig. 25. (a) Sketch of a possible set-up to perform microcontact measurements using one microelectrode and an extended counter-electrode. The microelectrode is contacted under the microscope by a sharp needle, (b) Set-up for two microelectrodes, (c) Evaporated Au microelectrodes on SrTiC>3 and the needlelike tungsten tip to contact the electrodes. Such a configuration is used to perform spatially resolved bulk conductivity measurements (Sec. 6.2). (d) Ag-coated YBajCujOs+s-microelectrodes on a SrTiC>3 polycrystal contacted by two tungsten tips. The corresponding local grain boundary measurements are discussed in Sec. 6.3. 

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