Originally Posted by Falanx

Compare and contrast the conductivity of metals with by definition, overlapping valence and conduction bands, and semiconductors, with their several orders of magnitude less charge carriers. In the case of solid solutions in metal, the minor alteration in lattice parameter with other metals with similar valence, in the case epecially of Ti alloys is the controlling factor. In the case of silicon, or gallium arsenide, you'd be doping a very poor conductor with electron sinks or providers, grossly atering electronic behaviour with just a few ppm impurity, but only because the material is instrinisically piss-awful at conducting.