Hexagonal high-temperature form of aluminium phosphate tridymite from X-ray powder data.
Similar to silica tridymite, AlPO4 tridymite shows a sequence of displacive phase transitions resulting in a dynamically disordered hexagonal high-temperature modification. Rietveld refinement reveals that the thermal motions of the tetrahedra can be described either by strongly anisotropic displacement parameters for oxygen or by split O atoms. Due to the ordered distribution of aluminium and phosphorus over alternating tetrahedra, the space group symmetry of high-temperature AlPO4 tridymite is reduced with respect to SiO2 tridymite from P6(3)/mmc to P6(3)mc.
Graetsch
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Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany. heribert.graetsch@ruhr-uni-bochum.de