On the Crystal Structure and Conductivity of Na3P

Abstract

As a potential material for Na-ion battery systems and on the basis of a structural discussion of compounds formerly believed to crystallize in the so-called Na3As type the structure of Na3P has been reinvestigated. Na3P is found to crystallize in the Cu3P type, analogous to Na3As and is described by a three times larger unit cell [P63cm, a = 8.61224(10) Å and c = 8.81949(10) Å] compared to the former model [P63/mmc, a = 4.9512(5) Å and c = 8.7874(13) Å]. As a structural manifestation of this symmetry reduction corrugated layers of Na and P atoms are observed which had formerly to be described as planar. The high purity of the material further enables the determination of its properties, showing mainly semiconducting behavior with a conductivity of 12 S·cm–1 at room temperature.