| Single-step, hydrothermal syntheses have been developed whereby phase-pure polycrystalline delafossite-like oxides (3R-polytype) can be prepared at low temperature (<210°C) and pressure (<20 atm). Delafossite oxides were investigated in a search for viable p-type transparent conducting oxides (TCOs), materials that simultaneously conduct electricity and transmit visible light. The structural and opto-electronic properties of the hydrothermally synthesized and the solid state synthesized CuAlO2 were measured.; Hydrothermally synthesized CuAlO2 exhibited a unique self-doping mechanism inherent to the synthesis. Rietveld refinement of powder X-ray data, corroborated by the results of inductively coupled plasma atomic emission spectroscopy and hydrogen reduction thermogravimetric analysis, revealed a formula unit of Cu0.925(8)Al1.075(8)O2.162(18) , where 7.5% extra aluminum occupies copper sites with intercalation of 0.162 oxygen anions per formula unit into the structure. This is the first report of oxygen intercalation into CuAlO2. A conductivity of 0.18 S/cm, which is one order of magnitude greater than the 1.48 x 10 -2 S/cm measured for its high temperature analog, was obtained. To date, this is the highest reported conductivity for any bulk sample of CuAlO2 and is superior to several reported values for thin film samples. The enhanced conductivity is attributed to a higher hole carrier concentration of 3.76 x 1021 +/- 0.40 x 10 21 cm-3 compared to 5.02 x 1020 +/- 3.02 x 1020 cm-3. Owing to this high carrier content, the transparency of hydrothermally synthesized CuAlO2 is one-third less than that of its solid state counterpart.; The universality of this synthesis technique to other delafossites was demonstrated by the synthesis of CuGaO2 and the solid solution Cu(A1-xGax)O2 (where 0 ≤ x ≤ 1). This solid solution had not been reported prior to this study. Furthermore, silver-based delafossites AgMO2 (where M = Ga and In) were also synthesized. The conductivities of AgGaO2 and AgInO2 were 0.05 and 0.001 S/cm, respectively. |
