Structure of β-AgGaO2; ternary I–III–VI2 oxide semiconductor with a wurtzite-derived structure

•Orthorhombic β-AgGaO2 with a wurtzite-derived β-NaFeO2 structure was synthesized.•Its structure was refined by Rietveld analysis of high-resolution XRD data.•Silver and oxygen tetrahedra are significantly distorted from an ideal tetrahedron.•The extent of this tetrahedral distortion is related to the band gap nature.•β-AgGaO2 is a metastable phase but is stable up to 690 °C in an O2 atmosphere.

The structure of the wurtzite-derived β-AgGaO2 was refined by Rietveld analysis of high-resolution powder diffraction data obtained using synchrotron X-ray radiation. The space group of the crystal is Pna21 with lattice parameters of a0=5.56175 Å, b0=7.14749 Å, and c0=5.46875 Å. The deviation of O–Ag–O and M–O–M bond angles from the regular tetrahedral angle of 109.5° was very large at ~8° and ~11°, respectively. The electronic structure of β-AgGaO2 is discussed based on its structure, and the indirect band gap of β-AgGaO2 was related to significant tetrahedral distortion. Although β-AgGaO2 decomposes into metallic silver and Ga2O3 at a high temperature in any atmosphere, β-AgGaO2 is stable up to 690 °C under an O2 atmosphere. No direct transformation from the wurtzite-derived phase to a delafossite phase occurs in β-AgGaO2.

Graphical abstractCrystal structure of β-AgGaO2 was refined by Rietveld analysis. AgO4 and O(Ag,Ga)4 tetrahedra are significantly distorted from ideal tetrahedron. Figure optionsDownload full-size imageDownload as PowerPoint slide