Influence of Cation on the Anion Frameworks and Properties of Four Lead Phosphates, A2PbBi2(PO4)2(P2O7) (A = Rb, Cs) and A2PbP2O7 (A = K, Rb).

Four new lead phosphates, A2PbBi2(PO4)2(P2O7) (A = Rb, Cs) and A2PbP2O7 (A = K, Rb), have been synthesized by the high-temperature solution method. A2PbBi2(PO4)2(P2O7) (A = Rb, Cs) compounds are isomorphic and crystallize into the space group of Pnma with different P-O groups, P2O7 and PO4. Rb2PbBi2(PO4)2(P2O7) exhibits an interesting structure that can be regarded as the stacking of Rb2Pb(P2O7) and BiPO4. A2PbP2O7 (A = K, Rb) compounds crystallize into the same space group of C2/c, but they are not isomorphic and exhibit different Pb-P-O frameworks. The influence of cation on the anion framework of A2PbP2O7 (A = K, Rb) has been discussed. The four compounds all melt congruently. Also, we have studied the cationic influence on the thermal and optical properties of A2PbBi2(PO4)2(P2O7) (A = Rb, Cs) and A2PbP2O7 (A = K, Rb).