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As an emerging transparent ceramic with extremely wide transmission range, the unique optical properties of ZnGa2O4 are of particular interest. In this work, ZnGa2O4 transparent ceramic with high optical quality was prepared by pressureless sintering and hot isostatic pressing. Its optical behavior was then comprehensively studied. The critical optical data, including refractive index, extinction coefficient, Abbé number, absorption coefficient in infrared region, and phonon frequency, were investigated. The indirect band gap and the phonon energy assisting indirect transition were determined as 4.10 and 0.17 eV, respectively. The modified Sellmeier equation and single‐oscillator dispersion relation were derived to describe the optical dispersion. Benefitting from the weaker tetrahedral Zn–O bond and heavier cationic masses, the infrared transmission range of ZnGa2O4 transparent ceramic was broadened significantly. Oxygen vacancies were suggested to induce the absorption in lower photon energy region of ZnGa2O4 transparent ceramic, which may enrich its functionalization. This work is meaningful for gaining overall insight into optical properties of transparent materials.

An in-depth insight into the effect of nitrogen substitution on structural stabilization is important for the design of new spinel-type oxynitride materials with tailored properties. In this work, the crystal structures of ordered and disordered LiAl 5 O 8 obtained by slow cooling and rapid quenching, respectively, were analyzed by a X-ray diffraction (XRD) Rietveld refinement and OccQP program. The variation in the bonding state of atoms in the two compounds was explored by the bond valence model, which revealed that the instability of spinel-type LiAl 5 O 8 crystal structure at room temperature is mainly due to the severe underbonding of the tetrahedrally coordinated Al cations. With the partial substitution of oxygen with nitrogen in LiAl 5 O 8 , a series of the nitrogenstabilized spinel Li y Al (16+x−y)/3 O 8−x N x (0 < x < 0.5, 0 < y < 1) was successfully prepared. The crystal structures were systematically investigated by the powder XRD structural refinement combined with 7 Li and 27 Al magic-angle spinning nuclear magnetic resonance. All the Li + ions entered the octahedra, while the Al resonances may be composed of multiple non-equivalent Al sites. The structural stability of spinel Li y Al (16+x−y)/3 O 8−x N x at ambient temperature was attributed to the cationic vacancies and high valence generated by the N ions, which alleviated the under-bonding state of the tetrahedral Al−O bond. This work provides a new perspective for understanding the composition−structure relationship in spinel compounds with multiple disorders.