| The Inverse Design approach to materials discovery was applied to developing materials that exhibit simultaneous p-type conductivity and optical transparency. Theoretical calculations predicted that Rh2ZnO4 and Cr2MnO4, well-known compounds with the spinel crystal structure, had the potential to be p-type transparent conducting oxides (p-TCOs). Bulk samples of these materials were synthesized, and their structural, optical, and electrical properties were characterized.;Theory predicted that Rh2ZnO4 was largely a line compound, with slight deviations toward Zn-excess at higher temperatures. This off-stoichiometry was predicted to be the source of excess holes and thus p-type conductivity in Rh2ZnO4. Additionally, new methods in density functional theory predicted that hole conduction in Rh 2ZnO4 occurred via band transport, instead of small polaron hopping. In this work, experimental X-ray diffraction (XRD) studies confirmed that Rh2ZnO4 exhibits small off-stoichiometry toward Zn-rich compositions at 975°C. High temperature electrical measurements confirmed p-type conductivity, and room temperature Hall effect measurements yielded a hole mobility of 0.18 cm2/Vs for a bulk polycrystalline sample.;In order to distinguish between band and polaron conduction, a revised analysis for high temperature electrical data was developed. This new analysis combines conductivity and thermopower data with theoretical calculations of the effective density of states in order to determine the behavior of the mobility with temperature. This method can be applied in the absence of a direct measurement of the temperature-dependence of the mobility. The results of this new method indicate that the behavior of Rh2ZnO4 is consistent with band conduction.;Although intrinsic Cr2MnO4 is electrically insulating, lithium was predicted to be an effective p-type dopant, occupying the tetrahedral (Mn) site. Combined neutron/X-ray measurements of a doped specimen confirmed the predicted site occupancy, and room temperature electrical measurements showed that lithium increases the conductivity of Cr2MnO 4 by several orders of magnitude to a value as high as 3.5 x 10 -2 S/cm. Cr2MnO4 was also predicted to be a band conductor, which was confirmed by the same revised analysis for high temperature electrical data that was developed for Rh2ZnO 4. At lower temperatures, electrical measurements found evidence of an activated mobility, which was attributed to grain boundary scattering instead of small polaron hopping. Optically, lithium doping causes increased absorption of visible light, which is consistent with the increased hole content. |
