weakly conducting materials?

In connection with a prototype design I'm developing for a meteorological measurement device, I'm looking for a readily available material with the
following physical properties:
1) Resistive, but not an insulator -- it will be used for resistive heating by passing a current (perpendicularly) through a thin sheet sandwiched between two flat metal conductors (like a leaky capacitor). Target resistivity of the material is in the range 10 to 10**4 ohm*meter at temperatures between 0 and 100 C.
2) A positive temperature coefficient (this apparently rules out silicon, for example).
3) Reasonably easy to work with in sheets or disks of order 0.1 mm thickness, 30 cm diameter.
4) Not subject to significant degradation or aging, even at sustained temperatures near 100 C for days or weeks at a time.
If anyone either knows offhand of a material matching the above description or can point me to a good tabulation of candidate materials, please let me know.
________________________________________ Prof. Grant W. Petty Atmospheric and Oceanic Sciences 1225 W. Dayton Street University of Wisconsin-Madison Madison, WI 53706
snipped-for-privacy@aos.wisc.edu Tel: (608) 263-3265 Fax: (608) 262-0166
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