Penternary Wurtzitic Nitrides Li 1- x Zn x Ge 2- x Ga x N 3 : Powder Synthesis, Crystal Structure, and Potentiality as a Solar-Active Photocatalyst.

We developed a new penternary wurtzitic nitride system Li 1- x Zn x Ge 2- x Ga x N 3 (0 ≤ x ≤ 1) by hybridizing LiGe 2 N 3 and ZnGeGaN 3 . Fairly stoichiometric fine powder samples were synthesized by the reduction-nitridation process at 900 °C. While the end member LiGe 2 N 3 possessed a relatively large band gap of 4.16 eV, the band gap of the developed penternary system varied in a broad range of 3.81 to 3.10 eV, showing promising responsivity to the solar spectrum. The crystal structure of LiGe 2 N 3 was precisely determined by time-of-flight neutron powder diffraction for the first time, revealing the complete ordering of Li and Ge in the Cmc 2 1 structure. The structural evolution from completely ordered LiGe 2 N 3 to fully disordered ZnGeGaN 3 was quantitatively analyzed by Rietveld refinement based on a partially disordered Cmc 2 1 model, and the obtained results were also supported by 71 Ga solid-state NMR spectroscopy. The synthesized Li 1- x Zn x Ge 2- x Ga x N 3 powder samples exhibited photocatalytic activities for the water reduction and oxidation reactions under solar light irradiation, with the H 2 evolution rate of 0.3-59.0 μmol/h and the O 2 evolution rate of 3.1-296.2 μmol/h, depending on the composition. Stable solar hydrogen generation of up to 48 h was demonstrated by the x = 0.80 sample, with the total amount of H 2 evolved over 1.6 mmol and an external quantum efficiency of 2.1%.