Crystal chemistry and predicted ionic conductivity of hydrothermally synthesized Na 9 Zn 2 (PO 4 ) 4 Cl

Single crystals of sodium zincophosphate chloride were obtained under medium-temperature hydrothermal conditions and its crystal structure was determined using low temperature X-ray diffraction. The Na 9 Zn 2 (PO 4 ) 4 Cl structure is formed from centrosymmetric pairs of strongly distorted trigonal bipyramids ZnO 4 Cl sharing Cl vertices, which are linked via PO 4 tetrahedra in the anionic layers neutralized by means of Na + cations. We show that the title compound represents the Zn alternative to Na 9 Zr(PO 4 ) 4 Cl. Both triclinic phosphates are characterized by close unit cell parameters and volumes. However, the formal replacement of one Zr 4+ for two Zn 2+ cations in their formulae is accompanied by significant structural transformations leading to the creation of various mixed-type anionic constructions: chains versus layers. Theoretical calculations of possible pathways of alkali ion migration through the structure and activation energies revealed that the Li substituted counterpart Li 9 Zn 2 (PO 4 ) 4 Cl can be considered as a potential solid electrolyte.