Three diphosphates, α-LiNaPO, LiPbBa(PO) and LiRb(PO): influences of co-substitution on the crystal structure.

Three diphosphates, α-LiNaPO, LiPbBa(PO) and LiRb(PO), were synthesized via a high-temperature solution method. α-LiNaPO crystallized into a non-centrosymmetric space group Ama2, while LiPbBa(PO) and LiRb(PO) crystallized into the centrosymmetric space groups C2/c and P1[combining macron]respectively. α-LiNaPO, LiPbBa(PO) and LiRb(PO) 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. LiNaPO possessed two phases, namely, α- and β-LiNaPO, 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.