Crystal Structure of Na2ZnP2O7: Reinvestigation

In the context of a detailed investigation of the luminescent properties of the Na2-xAgxZnP2O7 compounds, the structure of the pure sodium phosphates was "revisited." The crystal structure of Na2ZnP2O7 has been determined by X-ray diffraction using single crystals. A new model explaining the actual large unit cell (a=b=2177.1(3) pm, c=1028.5(2) pm, P42/n, Z=32) was determined by assuming the existence of twins. The structure is made up of [ZnP2O7] layers consisting of corners sharing [P2O7] groups and [ZnO4] tetrahedra, and the sodium atoms are located between the layers in 7- or 8-fold coordinated sites. This model is discussed with respect to the crystal chemistry of the monovalent cation zinc phosphate.