Current-voltage characteristics ohmic region

Ohmic losses AEohmic originate from (i) membrane resistance, (ii) resistance of CLs and diffusion layers, and (iii) contact resistance between the flow field plates. Although it is common practice to split current-voltage characteristics of an MEA into three regions— kinetic (low currents), ohmic (intermediate currents), and mass transport (high currents) [Winter and Brodd, 2004]—implicit separation of vt Afiohmic is not always straightforward, and thus studies of size and... 

Figure 22. Critical current as a function of temperature in magnetic field (from the right) 0, S, 10, and 14 T. Also indicated are the normal state (I), low-resistance ohmic state (II), and fully superconducting state (III). Inset are the current voltage characteristics representative of these regions. (Curve III has been expanded vertically 2000 times.)...

Another important aspect is the influence of the contact conditions on the estimation of the mobility from the current-voltage characteristics. This is customarily done by using the simple Shockley equation for the current. In Fig. 17 simulated transfer characteristics are depicted in the active and in the saturation regions. In the saturation region the representation = / Vgs) is chosen which is better suited for estimating the mobility in this region. In the simulation the mobility has been chosen as = 10 cm V Therefore, differences in the currents are caused solely by the different contact conditions. The estimation in the linear region (Fig. 17a) leads only to the correct value of the mobility, if all the contacts are ohmic ones. On the other hand, in saturation, the estimate leads only to an incorrect value for the mobility if the Cr/Au contact is the source. In the other case, Cr/Au as drain. 

The varistor characteristic associated to quality is the nonlinear coefficient (a). The higher their value, the greater the varistor efficiency. This coefficient can be obtained through empirical relationships current x voltage (Eq. 1) or current density versus electric field (Eq. 2) and expresses how much the material deviates from ohmic response when required, and it can be explained by a graphic representation (Figure 1) with distinct regions [12-15]. 

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