THE STRUCTURE OF THE CALCINED ALUMINOPHOSPHATE ALPO(4)-5 DETERMINED BY HIGH-RESOLUTION X-RAY AND NEUTRON POWDER DIFFRACTION

Rietveld refinements of the structure of calcined ALPO(4)-5 have been performed using synchrotron and neutron powder diffraction data. The h igh-resolution synchrotron X-ray diffraction pattern shows splitting o f some peaks, which indicates that the symmetry is lower than the hexa gonal cell observed in earlier studies. The neutron powder pattern is of lower resolution and no splitting is apparent, but the different sc attering lengths of Al and P, and the higher scattering power at high angle, provide a sound test for the different models investigated. Goo d lit of the neutron and synchrotron data were obtained in space group PccZ with cell parameters a=13.794(3) Angstrom, b=23.900(6) Angstrom, c=8.4168(6) Angstrom. In this space group there is a strict alternati on of Al and P in the framework, as the P-31 and Al-27 MAS NMR spectra indicate, and two crystallographically distinct 12-ring channels run parallel with the c axis.