Why Is ZnO Conductivity Non-Linear?

[eric336]

I want to understand the conductivity of ZnO. I know it is non-linear (that's why it is used in surge arrester to begin with), but can anyone enlighten me on why it is non-linear? Is it the function of electric field, current, or anything? I'd appreciate if you can provide the expression of conductivity.

 

[ChaseRLewis73]

I want to understand the conductivity of ZnO. I know it is non-linear (that's why it is used in surge arrester to begin with), but can anyone enlighten me on why it is non-linear? Is it the function of electric field, current, or anything? I'd appreciate if you can provide the expression of conductivity.

ZnO is a semiconductor material that naturally is n-type without doping. Thus it will have a good conductivity because it allows easy transitions to the conduction band (what it means to be n-type).

These slides go over it

http://www.iwe.kit.edu/plainhtml/lehre/mad/pdf/Nonlinear%20Resistors.pdf

If you look at the chart in here of current generation you can see how this works.
Basically it increases as the temperature increases to a point because the heat vibrations allow additional electrons to make the bandgap jump; however, eventually you reach a point where you keep pumping electrons into conductive band and it gets crowded so the conflicting movement causes a net loss of energy (the conflicting movement results in more heat loss than electrical conduction). So for a surge protector you can see how it would be valuable that when it gets oversaturated it heats up thus lowering the conductivity ... which if the current doesn't go down causes more heat ... and you see the pattern. More resistance = more heat which protects the circuit by increasing it's resistance when it heats up / when excessive current runs through it.

 

[Enthalpy]

It's attributed to grain boundaries but the debate is open
http://psec.uchicago.edu/library/microchannel_plates/zinc_oxide.pdf