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

Abstract

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 Prespectively. 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.