New gallium germanates with tunnel structures: α-Ga4GeO8 and Ga4Ge3O12

The structure of several gallium germanates has been established or confirmed (Ga4GeO8 α and β forms, Ga2GeO5, Ga4Ge3O12). Among them, α-Ga4GeO8 exhibits a new type of tunnel structure resulting from an intergrowth of GeO2 rutile elements in the β-gallia network. Large hexagonal tunnels take place at the junction of both lattices. This compound is the first term of a series having as general formula Ga4M2n−1O4n+4. Several other compounds M = Ge (n = 1, 2), Ti (n = 2, 3, 11 …), and Sn (n = 1) belong to the same family.