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 Ag ₃VO₄, 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(VO ₄)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 KAg ₁₁(VO₄)₄.