Variable framework structures and centricities in alkali metal yttrium selenites, AY(SeO3)2 (A = Na, K, Rb, and Cs)

Pure samples of a series of yttrium selenites, AY(SeO3)2 (A = Na, K, Rb, and Cs), were prepared through hydrothermal reactions using A2CO3, Y(NO3)3·6H2O, and SeO2. All four materials have 3D framework structures; however, they exhibit different channel geometries. The three-dimensional framework of NaY(SeO3)2 consists of zigzag chains of vertex-shared YO7 polyhedra and SeO3 linkers. KY(SeO3)2 and RbY(SeO3)2 reveal channels composed of corner-shared YO6 octahedra and SeO3 polyhedra. CsY(SeO3)2 exhibits a highly symmetric cage structure with radially spreading linkages of YO6 and SeO3 groups. Close structural examinations suggest that the cation size and coordination environment significantly influence the backbone architectures and their centricities. Second-harmonic generation (SHG) measurements on the powder sample of NaY(SeO3)2 reveal that the NCS selenite possesses a similar SHG efficiency to that of NH4H2PO4 (ADP).