High Pressure Synthesis of Rhombohedral Delafossite Structured $\alpha $-AgGaO$_{\mathrm{2}}$

In this work, we demonstrate for the first time the high pressure synthesis of $\alpha $-AgGaO$_{\mathrm{2}}$ via a solid state reaction of Ag$_{\mathrm{2}}$O and Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$. Synthesis experiments were carried out at pressures and temperatures up to 10 GPa and 600 \textdegree C, respectively, using a resistively-heated diamond anvil cell. Electron diffraction confirmed the rhombohedral delafossite crystal structure of the synthesized AgGaO$_{\mathrm{2}}$ and its corresponding lattice parameters of a $=$ 2.99 {\AA} and c $=$ 18.43 {\AA}. The vibrational modes analysis was also conducted using a combination of ab initio density functional theory (DFT) and Raman spectroscopy. This analysis yielded good agreement between the calculated Raman-active modes and experimental Raman data. Finally, the application of the GGA $+ \quad U$ formalism-based on DFT to calculate the electronic band structure of $\alpha $-AgGaO$_{\mathrm{2}}$ provided a more realistic theoretical band gap value than those reported previously.