Evaluation within a Phenomenological Model

7 is a simple mathematical expression which correctly describes these physically reasonable limits and which in accordance with the experimental data interpolates between them. 

As in this case we neither imply that the tunnelling is fluctuation enhanced nor assume the existence of image force corrected rectangular barriers, equs. 13 and 14 cannot be applied. The effective height Vq of the potential barriers in this case is identical with the activation energy of the electrical conductivity in the limit of high temperatures  

If the additional assumption is made that the conductivity for T- 0 is a tunnelling conductivity, the following equation is obtained with a(T=0) = oroo oxp(-Ti/To) for rectangular barriers  

For other shapes of the potential barrier, corrections are necessary which are typically of the order of 1. If the effective mass m of the mobile charge carriers is approximated by the free electron mass, the width w of the barriers can be calculated. 

The slope of y(T) decreases monotonically with increasing temperature for T- , it asymptotically approaches zero. For k3 T Vp, or(T) approaches a finite value Ooo Assuming a charge carrier concentration of 6% (100%) (related to the CH-unit), values of (Joo = 20 000 - 100 000 S/cm correspond 

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