Experimental Characterization of a Theoretically Designed Candidate p‑Type
Transparent Conducting Oxide: Li-Doped Cr<sub>2</sub>MnO<sub>4</sub>
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Abstract
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<sub>2</sub>MnO<sub>4</sub> 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<sup>5</sup> 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<sub>2</sub>MnO<sub>4</sub> 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