Kinetic control in the synthesis of metastable polymorphs: Bixbyite-to-Rh2O3(II)-to-corundum transition in In2O3

InOOH Bulk Crystals and Ultrathin Nanowires under Compression

InOOH bulk crystals and ultrathin nanowires have been investigated under high pressures by in situ synchrotron radiation X-ray diffraction measurements at ambient temperature. The anisotropic compression indicates that the b-axis is more compressible than the other two axes in InOOH under hydrostatic conditions. Two inflection points, which are associated with the hydrogen-bond strengthening, can be reflected in the plots of b/c ratio versus pressure (b/c-P plots). The size-induced enhancement of the bulk modulus can be visualized from the P-V plots. By comparing the differences in the compression of bulk InOOH and ultrathin nanowires, it is validated that the nanosize effects play an important role in the high-pressure behaviors of InOOH.

Structural and vibrational properties of corundum-type In2O3 nanocrystals under compression

This work reports the structural and vibrational properties of nanocrystals of corundum-type In₂O₃ (rh-In₂O₃) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and theoretical simulations on bulk rh-In₂O₃. Nanocrystalline rh-In₂O₃ showed stability under compression at least up to 20 GPa, unlike bulk rh-In₂O₃ which gradually transforms to the orthorhombic Pbca (Rh₂O₃-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk corundum-type In₂O₃ is discussed.

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°C) in highly basic conditions (pH>12). Subsequent calcination of InOOH at 375–700°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.

Surface chemistry and stability of metastable corundum-type In2O3

Highly correlated surface- and electrochemical characterization is linked to the metastability of rh-In₂O₃ for explanation of sensing and catalytic properties.

Compact low power infrared tube furnace for in situ X-ray powder diffraction

We describe the development and implementation of a compact, low power, infrared heated tube furnace for in situ powder X-ray diffraction experiments. Our silicon carbide (SiC) based furnace design exhibits outstanding thermal performance in terms of accuracy control and temperature ramping rates while simultaneously being easy to use, robust to abuse and, due to its small size and low power, producing minimal impact on surrounding equipment. Temperatures in air in excess of 1100 °C can be controlled at an accuracy of better than 1%, with temperature ramping rates up to 100 °C/s. The complete "add-in" device, minus power supply, fits in a cylindrical volume approximately 15 cm long and 6 cm in diameter and resides as close as 1 cm from other sensitive components of our experimental synchrotron endstation without adverse effects.