The structure of the calcined aluminophosphate ALPO4-5 determined by high-resolution X-ray and neutron powder diffraction

Abstract

Rietveld refinements of the structure of calcined ALPO₄-5 have been performed using synchrotron and neutron powder diffraction data. The high-resolution synchrotron X-ray diffraction pattern shows splitting of some peaks, which indicates that the symmetry is lower than the hexagonal cell observed in earlier studies. The neutron powder pattern is of lower resolution and no splitting is apparent, but the different scattering lengths of Al and P, and the higher scattering power at high angle, provide a sound test for the different models investigated. Good fits of the neutron and synchrotron data were obtained in space group Pcc2 with cell parameters a= 13.794(3)Å, b= 23.900(6)Å, c= 8.4168(6)Å. In this space group there is a strict alternation of Al and P in the framework, as the ³¹P and ²⁷Al MAS NMR spectra indicate, and two crystallographically distinct 12-ring channels run parallel with the c axis.