The decagonal superstructure Al71Co13Ni16 and its relation to the basic decagonal phase Al71Co7Ni22

Stable Al71Co13Ni16 represents a commensurate quasiperiodic superstructure of decagonal Al71Co7Ni22 .The structure was analysed with a large X-ray dif fraction data set. All Bragg peaks observable on an imaging plate detector were recollected on a six-circle diffractometer at the synchrotron source H asylab. The Bragg peak positions were determined with high accuracy and the resolution in perpendicular space was optimized by collecting all observab le reflections including the weak satellite reflections. The five-dimension al Bravais lattice was determined uniquely by a novel Patterson technique. The 'translation' vectors of the 'quasilattice' were separated from the dec oration vectors and the proper metric was derived. Consequences of misindex ing the diffraction pattern, especially with respect to scaling, are discus sed. A comparison of the superstructure metric with its average structure r evealed the structural relationships.