High-pressure synthesis of rhombohedral α-AgGaO2 via direct solid state reaction

Abstract In this work, we demonstrate the application of high pressure conditions to enable the direct synthesis of α-AgGaO2 via a solid state reaction of Ag2O and Ga2O3. Synthesis experiments were carried out at pressures and temperatures up to ∼10 GPa and ∼600 °C, respectively, using a resistively-heated diamond anvil cell. Thus synthesized α-AgGaO2 samples were characterized and their chemical composition and crystal structure were confirmed. In particular, electron diffraction confirmed the rhombohedral delafossite crystal structure of the synthesized AgGaO2 and its corresponding lattice parameters of a = 2.99 A and c = 18.43 A. 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 + U formalism-based on DFT to calculate the electronic band structure of α-AgGaO2 provided a more realistic theoretical band gap value than those reported previously.