REFINEMENT OF THE CRYSTAL STRUCTURE OF β-Mg₂P₂O₇

The crystal structure of Mg₂P₂O₇ reported by Lukaszewicz has been refined by least squares analysis. Data of the hkl type with O ≤ k ≤ 6 have been used to obtain improved atomic parameters. The central oxygen atom of the P₂O₇⁻⁴ is found to have enhanced thermal motion in the plane perpendicular to the P—P vector. Thus the P—O—P bond angle appears to be linear in this phase because of a thermal averaging of the position of the central oxygen atom. This conclusion is in agreement with that obtained by Lazarev from infrared studies.