Phosphates with Two Types of Isolated P-O Groups: Noncentrosymmetric Na6Sr2Bi3(PO4)(P2O7)4 and Centrosymmetric Cs2CaBi2(PO4)2(P2O7)

Inorganic phosphates are of great interest, because of their rich structural chemistry and multiple functional properties. Compared with the phosphates that only contain the solely condensed P-O groups, the phosphates with various condensed P-O groups are less reported, especially for the noncentrosymmetric (NCS) ones. Here, two new bismuth phosphates, Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ and Cs₂CaBi₂(PO₄)₂(P₂O₇), were synthesized by the solid-state reaction and both structures contain two types of isolated P-O groups. Remarkably, Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ crystallizes in the tetragonal space group P4̅2₁c, which represents the first NCS bismuth phosphate with PO₄ and P₂O₇ groups. Detailed structural comparisons among Bi³⁺-containing alkali/alkaline-earth metal phosphates show that the ratios of cations/phosphorus profoundly influence the condensed degree of P-O groups. Ultraviolet-visible-near-infrared (UV-vis-NIR) diffusion spectra show that both compounds have the relatively short UV cutoff edges. And Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ has a second-harmonic generation response of 1.1 × KDP. The first-principles calculations are carried out to understand the structure-performance relationship.

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

We reported the synthesis, structure, characterization and first-principles calculations of diphosphates, α-Li₂Na₂P₂O₇, Li₈Pb₃Ba(P₂O₇)₄ and Li₇Rb(P₂O₇)₂, and studied the influences of co-substitution on the crystal structure.

An alkali metal phosphate RbPbBi2(PO4)3 with three kinds of disorder: the effect of isolated soft cation units on the crystal structure

We have reported a new phosphate, RbPbBi₂(PO₄)₃ with three kinds of disorder, and a concept of isolated soft units has been firstly put forward to study the origin of structural distortions and disorder.