Improved conductivity has been achieved by controllable substitution of an ultraviolet electronic conductor. The transparent conducting oxide system, H-doped Ca12Al(14−x)SixO(33+x/2) with x=0−4, exhibits a conductivity strongly dependent on the substitution level. Four-point direct current conductivity increases with x from 0.15 to 0.61 S/cm at room temperature. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Si-substituted system with x=0, 2, and 4. Furthermore, the Seebeck coefficient is composition dependent suggesting the existence of an activated mobility associated with small polaron conduction. ©2007 American Institute of Physics