Interpretation of sigma-Al2O3 real structure by means of X-ray investigations and the videographic method

Single crystals of sigma-Al2O3 have been studied to get more information ab out the real structure. Both X-ray-investigations and the videographic meth od have been employed to characterise the ordering scheme of the aluminium vacancies in the lattice of sigma-Al2O3 A description of the satellite syst ems of sigma-Al2O3 phase I and II is given and it is shown that the orderin g of the aluminium vacancies in phase II can be described by means of inter vacancy correlation vectors parallel to [100] and parallel to [101]. Phase I can be described considering additional correlation vectors parallel to [ 203] and parallel to [302]. Additional directions < 401 > result from the i nterpretation of the 1(st) and 2(nd) layer precession photographs.