Experimental Characterization of a Theoretically Designed Candidate p-Type Transparent Conducting Oxide: Li-Doped Cr₂MnO₄

The development of a p-type transparent conducting oxide (p-TCO) requires the deliberate design of a wide band gap and high hole conductivity. Using high-throughput theoretical screening, Cr 2 MnO 4 was earlier predicted to be a p-TCO when doped with lithium. This constitutes a new class of p-TCO, one based on a tetrahedrally coordinated d 5 cation. In this study, we examine and experimentally validate a few central properties of this system. Combined neutron diffraction and anomalous X-ray diffraction experiments give site occupancy that supports the theoretical prediction that lithium occupies the tetrahedral (Mn) site. The lattice parameter of the spinel decreases with lithium content to a solubility limit of [Li]/([Li] + [Mn]) ∼ 9.5%. Diffuse reflectance spectroscopy measurements show that at higher doping levels the transparency is diminished, which is attributed to both the presence of octahedral Mn and the increased hole content. Room-temperature electrical measurements of doped samples reveal an increase in conductivity of several orders of magnitude as compared to that of undoped samples, and high-temperature measurements show that Cr 2 MnO 4 is a band conductor, as predicted by theory. The overall agreement between theory and experiment illustrates the advantages of a theory-driven approach to materials design.