Three diphosphates, α-Li2Na2P2O7, Li8Pb3Ba(P2O7)4 and Li7Rb(P2O7)2: influences of co-substitution on the crystal structure

Three diphosphates, alpha-Li2Na2P2O7, Li8Pb3Ba(P2O7)(4) and Li7Rb(P2O7)(2), were synthesized via a high-temperature solution method. alpha-Li2Na2P2O7 crystallized into a non-centrosymmetric space group Ama2, while Li8Pb3Ba(P2O7)(4) and Li7Rb(P2O7)(2) crystallized into the centrosymmetric space groups C2/c and P1respectively. alpha-Li2Na2P2O7, Li8Pb3Ba(P2O7)(4) and Li7Rb(P2O7)(2) could be obtained by co-substitution from each other. Also, we found that the high valence state and small atomic radius of the substituted cations resulted in a larger cation-cation distance, which led to a lower dimension of the structure. Li2Na2P2O7 possessed two phases, namely, alpha- and beta-Li2Na2P2O7, and their second harmonic generation (SHG) responses were compared. We also reported the syntheses, IR spectra, UV-vis-NIR diffuse reflectance spectroscopy data, thermal properties and first principles calculations of the title compounds.