LAUSR

Three diphosphates, α-Li2Na2P2O7, Li8Pb3Ba(P2O7)4 and Li7Rb(P2O7)2, were synthesized via a high-temperature solution method. α-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 P1[combining macron]respectively. α-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, α- and β-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.