A study of composition effects on bandgaps on a series of new alkali metal aluminum/gallium iodates

Four new alkali metal aluminum/gallium iodates, namely A2M(IO3)4(H0.5IO3)2 (A=K, Rb; M=Al, Ga), have been successfully obtained by hydro-thermal reaction and structurally characterized through the single-crystal X-ray diffraction analysis. They are isostructural and crystallize in space group P-1 (no.2) with one formula unit in each unit cell. The scarcely half protonation H0.5IO3 building units were identified, and their structures feature isolated [M(IO3)4(H0.5IO3)2]2- anions that are separated by alkali metal cations. Optical diffuse reflectance spectrum measurements associated with Tauc analysis shows direct energy gaps which are in good agreement with theoretical calculation prediction. Moreover, this study also indicates that electronic properties are mainly determined by IO3 and H0.5IO3 anionic units, alkali metal cations show a remarkable effect on their energy gap values, whereas the impacts of the 13 main group elements aluminum and gallium are insignificant.