12 research outputs found
Structural and Thermal Properties of Ternary Narrow-Gap Oxide Semiconductor; Wurtzite-Derived β‑CuGaO<sub>2</sub>
The
crystal structure of the wurtzite-derived β-CuGaO<sub>2</sub> was refined by Rietveld analysis of high-resolution powder diffraction
data obtained from synchrotron X-ray radiation. Its structural characteristics
are discussed in comparison with the other I–III–VI<sub>2</sub> and II–VI oxide semiconductors. The cation and oxygen
tetrahedral distortions of the β-CuGaO<sub>2</sub> from an ideal
wurtzite structure are small. The direct band-gap nature of the β-CuGaO<sub>2</sub>, unlike β-Ag(Ga,Al)O<sub>2</sub>, was explained by
small cation and oxygen tetrahedral distortions. In terms of the thermal
stability, the β-CuGaO<sub>2</sub> irreversibly transforms into
delafossite α-CuGaO<sub>2</sub> at >460 °C in an Ar
atmosphere. The transformation enthalpy was approximately −32
kJ mol<sup>–1</sup>, from differential scanning calorimetry.
This value is close to the transformation enthalpy of CoO from the
metastable zincblende form to the stable rock-salt form. The monovalent
copper in β-CuGaO<sub>2</sub> was oxidized to divalent copper
in an oxygen atmosphere and transformed into a mixture of CuGa<sub>2</sub>O<sub>4</sub> spinel and CuO at temperatures >350 °C.
These thermal properties indicate that β-CuGaO<sub>2</sub> is
stable at ≤300 °C in both reducing and oxidizing atmospheres
while in its metastable form. Consequently, this material could be
of use in optoelectronic devices that do not exceed 300 °C