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Reading about old-fangled radios the reference quoted below indicates it was/is possible to use a rusted razor (or perhaps any similar thin corroded metal strip) as a detector.

Some resourceful GIs found that a crude crystal set could be made from a coil made of salvaged wire, a rusty razor blade and a pencil lead for a diode. By lightly touching the pencil lead to spots of blue on the blade, or to spots of rust, they formed what is called a point contact diode and the rectified signal could be heard on headphones or crystal ear pieces.

How does a rusted razor perform the same task as a PN junction? Is it merely that rust (being minute oxidized metallic particles) migrates under the influence of the electrical field?

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This isn't a great answer since all the papers I could find are behind paywalls, but ferric oxide is a semiconductor and depending on it's exact stochiometry can be n type or p type.

If you know someone in academia with access have a look at:

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