Low-temperature electrical conductivity of

We report the electrical conductivity between 2 and 300 K for across the composition-controlled metal - insulator (m - i) transition. Using a method first suggested by Möbius, we identify the critical concentration to be 0.3 for the m - i transition. The negative temperature coefficient of resistivity observed at low temperatures in the metallic phase follows a temperature dependence characteristic of disorder effects. The semiconducting compositions do not show a simple activation energy but exhibit variable-range hopping at high temperatures confirming that the m - i transition in this system is driven by increasing disorder effects.