Syntheses, Structure and Characterization of Three New Mg-containing Phosphates with Deep-UV Cut-off Edges
Three new Mg-containing phosphates AMg2P3O10 (A = Li, Cs) and Rb2MgP2O7 have been successfully synthesized by high temperature solution method. The single crystal X-ray diffractions show they crystallize in different space groups, P21/m for LiMg2P3O10, Pbcn for CsMg2P3O10 and Pnma for Rb2MgP2O7. Interestingly, their structures contain two different types of P-O connect modes, i.e. P3O10 trimers in AMg2P3O10 (A = Li, Cs) and P2O7 dimers in Rb2MgP2O7. Correspondingly, the Mg2+-centered polyhedra also exhibit three different polymerizations, including one-dimensional (1D) [MgO6]∞ infinite chains in LiMg2P3O10, the Mg2O8 dimers in CsMg2P3O10 and the isolated MgO5 square pyramids in Rb2MgP2O7. Detailed structural analysis indicates that the different size of A-site cations and flexible coordination of Mg2+ cations are responsible for the structural differences. Furthermore, the optical measurements of three compounds show that they all possess deep-UV absorption cut-off edges (< 190 nm). And their thermal properties and the bond valence sum difference map (BVS-DM) calculations are also studied.