Crystal structure of Na₂ZnP₂O₇: Reinvestigation

In the context of a detailed investigation of the luminescent properties of the Na(2-x)Ag(x)ZnP₂O₇ 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. (C) 2000 Academic Press.