Thermal expansion and thermally induced variations of the crystal structure of AlPO4 low cristobalite
Graetsch, Heribert A.
published: Jul 15, 2003
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.