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Mixed transition metal spinel oxide polaron conductors can exhibit resistivities on the order of milliohm-cm making them attractive candidates for electro-optic applications. While high transparency is achieved at long wavelengths, in contrast to free-carrier conductors, transparency at shorter wavelengths is somewhat compromised owing to weak absorption associated with transitions between the resident d-electron levels. Thus, NiCo2O4, exhibits an intrinsic p-type conductivity of several milliohm-cm but registers high transparency only at wavelengths longer than about 2 micrometers. However, when cobalt is replaced by rhodium, the transparency region is extended to the green region of the spectrum. In recent work, p-type conductivity has been observed in mixed copper manganese spinel oxide films deposited by both PLD and solution spin-casting approaches. Film deposition parameters are critical to achieving the conducting state and require a highly oxidizing environment during deposition or in subsequent post-deposition treatment. XRD and Raman measurements are used to characterize phase homogeneity of films derived using both processing approaches while the cation charge state distribution is evaluated from XPS measurements. The co-existence of divalent copper and trivalent manganese and the presence of a homogeneous spinel phase are key to achieving high conductivity in these materials. The copper manganese spinel film shows a weak blue color commensurate with increased visible transparency. Ongoing work on new spinel oxide compositions is driven by DFT calculations which suggest that higher transparency at visible wavelengths can be achieved by substitution with cations residing deeper in the periodic table. |