Scaled-up solvothermal synthesis of nanosized metastable indium oxyhydroxide (InOOH) and corundum-type rhombohedral indium oxide (rh-In2O3)

Phase pure metastable indium oxyhydroxide (InOOH) with crystallite size in the range ca. 2-7 nm is synthesized by a nonaqueous solvothermal synthesis route in ethanol. The influence of synthesis parameters such as temperature, basicity (pH), synthesis time, and water content is carefully addressed. T-pH maps summarize the impact of synthesis temperature and pH and reveal that phase pure InOOH is obtained in water-free solutions at mild temperatures (150-180 degrees C) in highly basic conditions (pH > 12). Subsequent calcination of InOOH at 375-700 degrees C in ambient air atmosphere results in metastable nanoscaled rhombohedral indium oxide (rh-In2O3). The synthesis protocol for phase pure nanocrystalline InOOH material was successfully upscaled allowing for obtaining ca. 3 g of phase-pure InOOH with a yield of ca. 78 %. The upscaled InOOH and rh-In2O3 batches are now available for a detailed in-situ characterization of the mechanism of decomposition of InOOH to rh-In2O3 to c-In2O3 as well as for the characterization of the functional properties of InOOH and rh-In2O3 materials.