In Situ XRD Studies of ZnO/GaN Mixtures at High Pressure and High Temperature: Synthesis of Zn-Rich (Ga1-xZnx)(N1-xOx) Photocatalysts

The high-pressure, high-temperature conditions for the synthesis of Zn-rich (Ga1-xZnx)(N1-xOx) solid solutions from mixtures of ZnO/GaN were explored using synchrotron-based in situ time-resolved X-ray diffraction (XRD). Following a new synthetic path, (Ga1-xZnx)(N1-xOx) solid solutions with a Zn content up to similar to 75% were prepared for the first time. The structures of the (Ga1-xZnx)(N1-xOx) solid solutions were characterized by XRD and X-ray absorption fine structure (XAFS) analyses and were in excellent agreement with the predictions of density functional calculations. These materials adopt a wurtzite crystal structure with metal-N or metal-O bond distances in the range of 1.95-1.98 angstrom. Although the (Ga1-xZnx)(N1-xOx) solid solutions seem to be stable over the full range of compositions, no ideal solid solution formation was observed. In all cases, the lattice parameters were larger than those of ideal solid solutions. The variation of the lattice parameter c showed an upward double bowing curve, as was predicted by theoretical calculations. Also, no ideal behavior was observed in the electronic properties of the (Ga1-xZnx)(N1-xOx) solid solutions. X-ray absorption spectra at the Zn and Ga K-edges of the (Ga1-xZnx)(N1-xOx) systems showed significant electronic perturbations with respect to ZnO and GaN. The synthesized (Ga1-xZnx)(N1-xOx) solid solution with a Zn content of 50% displayed the ability to absorb visible light well above 500 nm. This material has a great potential for splitting water under visible light irradiation. The availability of (Ga1-xZnx)(N1-xOx) solid solutions with a high Zn content opens the door to fully explore the application of these materials in photocatalysis.