Original paper

Thermal expansion and thermally induced variations of the crystal structure of AlPO4 low cristobalite

Graetsch, Heribert A.

Abstract

The crystal structure of AlPO4 low cristobalite was refined at 25, 75, 125, 150, 175 and 200 °C from X-ray powder data with the Rietveld method confirming the orthorhombic symmetry C2221 with very small deviation from tetragonal symmetry. Upon heating, the atoms are shifted by 0.022(3) Å on the average towards their average positions in high temperature cristobalite. The volume gap at the displacive α-β transformation at 202 °C is slightly larger (4.6 %) than that of silica cristobalite (4.2 %). The high temperature modification was refined at 200 °C in space group F43m using a split atom model for oxygen.

Keywords

thermal expansionalpo4cristobalitespontaneous strainphase transformation