KAg11(VO4)4 as a candidate p-type transparent conducting oxide.

For a material to be a good p-type transparent conducting oxide (TCO), it must simultaneously satisfy several design principles regarding its bulk and defect phase thermochemistry, its optical absorption spectrum, and its electric transport properties. Recently, we predicted Ag3VO4 to be p-type but with low conductivity and an optical band gap not large enough for transparency. To improve on the transport and optical properties of Ag3VO4, we searched an extended material space including quaternary compounds based on Ag, V, O, and an additional atom for a new candidate p-type TCO. From this set of quaternary materials, we selected KAg11(VO4)4, a known oxide with a crystal structure related to that of Ag3VO4. Notably, one could expect a possible enhancement of the concentration of hole producing Ag-vacancy defects in KAg11(VO4)4 due to its different local geometries of Ag atoms (2- and 3-fold coordinated) with respect to the 4-fold coordinated Ag atoms in Ag3VO4. By performing first-principles calculations, we found that KAg11(VO4)4 is an intrinsic p-type conductor and can be synthesized under conditions similar to those predicted for the synthesis of Ag3VO4. However, we predict that the intrinsic hole content in KAg11(VO4)4 is similar to that in Ag3VO4 even though KAg11(VO4)4 contains 2- and 3-fold coordinated Ag, hole producing sites with a lower defect formation energy than the 4-fold coordinated one. Our calculation demonstrates that the advantage from lower coordination number of the Ag atom in KAg11(VO4)4 can be offset by the change in the range of Ag chemical potential in which synthesis is allowed due to the oxide phases that Ag forms with K and that energetically compete with KAg11(VO4)4.