MIMIIP3O9 (MI = Rb, MII = Cd, Mg, Ca; MI = Cs, MII = Pb, Sr; MI = K, MII = Mg): Cation Substitution Application in Cyclophosphate Family and Nonlinear Optical Properties

By the application of cation substitution, five new members of cyclophosphates, RbCdP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9, were obtained by a high-temperature melt method and structurally analyzed. The five compounds have identical stoichiometries, and all of them feature a three-dimensional network, which consists of MIIO6 (MII = Cd, Mg, Ca, Pb, Sr) octahedra and cyclic P3O9 units, while alkali-metal atoms are located within the network. However, RbCdP3O9 and CsPbP3O9 belong to the asymmetric space groups Pc2 and Pna21, respectively, and the other three compounds belong to orthorhombic space group Pnma. Detailed structure comparisons in the MI-MII-P-O and (MIMIIP3O9)n (n = 1, 2, 6) systems are discussed. Remarkably, KMgP3O9 as one of the cyclophosphate members exhibits a second harmonic generation (SHG) intensity about 0.2 times that of KH2PO4 (KDP), RbCdP3O9, and CsPbP3O9 also show SHG responses 0.1 times that of KDP. In addition, the related optical properties are discussed. Furthermore, theoretical calculations and dipole moments were calculated to explain the relation of structure and optical properties.