  Metallic conductors that are optically transparent represent a rare breed of
generally contraindicated physical properties that are nevertheless critically
needed for application where both functionalities are crucial. Such rare
materials have traditionally been searched in the general chemical neighborhood
of compounds containing metal oxides, expected to be wide gap insulators that
might be doped to induce conductivity.Focusing on the family of 18 valence
electron ABX compounds we have searched theoretically for the ability of the
compound's electronic structure to simultaneously lead to optical transparency,
in parallel with the ability of its intrinsic defect structures to produce
uncompensated free holes.This led to the prediction of a stable, never before
synthesized TaIrGe compound made of all-metal heavy atom compound as the "best
of class" from the V-IX-IV group. Laboratory synthesis then found it to be
stable in the predicted crystal structure and p-type transparent conductor with
measured strong direct absorption of 3.36 eV and remarkably high (albeit not
predicted) hole mobility of 2730 cm2/Vs at room temperature. This methodology
opens the way to future searches of transparent conductors in unexpected
chemical groups.
