SYNTHESIS, STRUCTURES OF AIPO4-C AND AIPO4-D, AND THEIR TOPOTACTIC TRANSFORMATION

AlPO4-H3 was synthesized and converted into AlPO4-C, which was transformed into AlPO4-D. The structures of the alumino-phosphates AlPO4-C and AlPO4-D have been determined from an X-ray powder study, and the topotactic transformation between these two structure types is described. The Rietveld refinement of AlPO4-C in space group Pbca (a=19.82, b=10.05, c=8.94 A ̊) converged with RF=0.051 and Rwp=0.170. The Rietveld refinement of AlPO4-D in space group Pca21 (a=19.19, b=8.58, c=9.80 A ̊) converged with RF=0.115 and Rwp=0.203. In the topotactic transformation of AlPO4-C to AlPO4-D, the UUDD (double-crankshaft) chains of AlPO4-C change to UDUD (narsarsukite-type) chains in AlPO4-D. The 4.82 layers in both structures are preserved, while one interlayer oxygen atom undergoes a reconstructive shift. © 1990.