Graphite and Conductivity

BIG BIG AL

Just popping a random question out there:

For my science fair project, I tested how temperature affects the conductivity of graphite. I hypothesized that graphite would act the same as metals - better conductivity at low temperatures, less conductivity at higher temperatures. I reasoned that since·heat disrupts electron flow in metals, leading to higher electric resistance, the same should occur in graphite. Contrary to my hypothesis, I found that graphite conducts electricity better at higher temperatures, rather than at lower temperatures.

This is my question: How does temperature affect the molecular structure of graphite so that it conducts electricity better at higher temperatures?

I would appreciate any help.

skylight

some metals such as tungsten have whats called a negative coefficient of resistance

http://www.allaboutcircuits.com/vol_1/chpt_12/6.html

http://en.wikipedia.org/wiki/Temperature_coefficient#Negative_temperature_coefficient

ElectricAye

Unlike amorphous carbon (which does not conduct electricity very well), graphite has a definite structure that gives it special properties. Its stacked plate-upon-plate structure is what makes it slippery but I suppose it also does some strange things to how the electrons and phonons interact.

I think a better way to pose this question might be: Why does graphite have a negative temperature coefficient of resistance?

It probably has much to do with graphite's conduction band.

Check out the following links for ideas:

www.seas.upenn.edu/~chem101/sschem/conduction.html#graphite

Read about the conduction band model: en.wikipedia.org/wiki/Thermistor

en.wikipedia.org/wiki/Conduction_band

www.everyscience.com/Chemistry/Inorganic/Carbon/a.1189.php

hope that helps get you started,
Mark

Post Edited (ElectricAye) : 2/10/2010 4:49:48 PM GMT