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

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 highthroughput 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.

Design of Semiconducting TetrahedralMn1−xZnxOAlloys and Their Application to Solar Water Splitting

“…For hole carriers, the transport mechanism depends on the structure: In the octahedral coordination environment of RS MnO, the small-polaron formation is exothermic, i.e., the self-trapping energy E ST for the process Mn þII þ h þ → Mn þIII is negative (here, h þ denotes a positively charged hole carrier at the VBM). However, in the hypothetical zinc-blende structure of MnO, the small-polaron formation was found to be suppressed because of the tetrahedral coordination [8], which motivated studies on ternary wide-gap Mn(II) oxides with tetrahedral Mn coordination [37,38]. For the purpose of the present work, we performed calculations of the small-polaron binding energy for MnZnO alloys and for ZnO.…”

Perovskite Sr‐Doped LaCrO3 as a New p‐Type Transparent Conducting Oxide

“…As a result, the Cr 3 d 3 electron configuration plays a critical role in enhancing the p‐type conductivity in CuCrO 2 in a similar way as in LSCO. Cr 2 O 3 and MnCr 2 O 4 have recently been identified as parent compounds for p‐TCOs . Therefore Cr 3+ cations should be considered for future design of high‐performance p‐TCOs.…”

Conducting mechanism in the epitaxialp-type transparent conducting oxideCr2O3:Mg

“…Previously, ac impedance spectroscopy has been used to estimate the contribution of grain boundaries to the bulk electrical conductivity [31,39,40]. However, this is not investigated here as the difference is expected to be small due to the low number of such defects in epitaxial samples.…”

“…Indeed, it is heavily discussed in the literature what model is applicable for p-type TCOs. [31] To fully distinguish whether the SPH model is appropriate, high temperature measurements of conductivity and thermopower are typically analyzed to ascertain whether an activated mobility exists [32]. This alone is not enough to distinguish the mechanism definitively without an understanding of the effective density of states [33].…”