Na-α′-GeGaON Solid Solution Analogous to α′-SiAlON: Synthesis, Crystal Structure, and Potentiality as a Photocatalyst

We demonstrated, for the first time, formation of the Na-α′-GeGaON (NamGe12–(m+n)­Gam+nOnN16–n) solid solution, an analogue of the well-established α′-SiAlON system. We successfully synthesized single-phase powder samples by reduction–nitridation of Na2CO3–GeO2–Ga2O3, in the solubility range of m ≈ 0.8–1.7 with n ≈ 0.2–0.3. The Rietveld refinement of powder X-ray diffraction data for Na-α′-GeGaON was conducted on the basis of the space group P31c of α′-SiAlON, and the refinement converged with RB = 1.78% and RF = 1.02% for the composition of Na1.26(1)Ge10.50­Ga1.50O0.24(1)N15.76(1), indicating reliably the isomorphism between the SiAlON and GeGaON systems. The results of 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy clearly showed a single peak at the chemical shift of ∼16 ppm, further proving the accommodation of Na in the α′-GeGaON matrix with the expected coordination environment. The synthesized Na-α′-GeGaON exhibited stable photocatalytic activity for the evolution of H2 from water under ultraviolet irradiation, which was comparable to that attained by β-Ge3N4.