title: Structural and thermal properties of ternary narrow-gap oxide semiconductor; wurtzite-derived β-CuGaO2.
abstract: The crystal structure of the wurtzite-derived β-CuGaO2 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-VI2 and II-VI oxide semiconductors. The cation and oxygen tetrahedral distortions of the β-CuGaO2 from an ideal wurtzite structure are small. The direct band-gap nature of the β-CuGaO2, unlike β-Ag(Ga,Al)O2, was explained by small cation and oxygen tetrahedral distortions. In terms of the thermal stability, the β-CuGaO2 irreversibly transforms into delafossite α-CuGaO2 at >460 °C in an Ar atmosphere. The transformation enthalpy was approximately -32 kJ mol(-1), 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-CuGaO2 was oxidized to divalent copper in an oxygen atmosphere and transformed into a mixture of CuGa2O4 spinel and CuO at temperatures >350 °C. These thermal properties indicate that β-CuGaO2 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.
authors: Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors: Hiraku
authors: H
authors: Nagatani
authors: Issei
authors: I
authors: Suzuki
authors: Masao
authors: M
authors: Kita
authors: Masahiko
authors: M
authors: Tanaka
authors: Yoshio
authors: Y
authors: Katsuya
authors: Osami
authors: O
authors: Sakata
authors: Shogo
authors: S
authors: Miyoshi
authors: Shu
authors: S
authors: Yamaguchi
authors: Takahisa
authors: T
authors: Omata