Vanadium Dioxide is an interesting material. It functions as a metal at some temperatures and then as an insulator at other temperatures. The microscopic reason for the transition is unknown but the ways this can be used is interesting.
Transition metal oxides make for interesting studies. They are normally an insulator that does not allow any current to flow but increase the temperature to a defined transition temperature (47C-68C) and the current starts to flow. There have been good research publications, like this one, that makes the conduction happen in the presence of Tungsten but the interesting effect is also followed by the change of material from transparent to reflective. This has led to its potentially utility in windows that change from reflective to transparent and back though it has not been commercialized.
Lawrence Livermore Laboratory recently reported that the material that could work like a microactuator that enables the movement of flagella like hair on the particle to move in response to electrical heat, laser or just heat. This is just another property that could enable it to be used in materials that would change the conduction but also move the particle in fluids.