Averaging of the electron effective mass in multicomponent transparent conducting oxides

We find that layered materials composed of various oxides of cations with $s^2$ electronic configuration, $XY_2$O$_4$, $X$=In or Sc, $Y$=Ga, Zn, Al, Cd and/or Mg, exhibit isotropic electron effective mass which can be obtained via averaging over those of the corresponding single-cation oxide constituents. This effect is due to a hybrid nature of the conduction band formed from the s-states of {\it all} cations and the oxygen p-states. Moreover, the observed insensitivity of the electron effective mass to the oxygen coordination and to the distortions in the cation-oxygen chains suggests that similar behavior can be expected in technologically important amorphous state. These findings significantly broaden the range of materials as efficient transparent conductor hosts.