The crystal structure of the layered compound Na2Al2B2O7 was re-examined. It was found that stacking faults could be introduced easily in the sequence of [Al2B2O7]∞2− lamellae. Both rotation and reflection twinning could form in the crystal by introducing appropriate stacking faults. A domain of the Sr2Be2B2O7-type structure might occur at the twin boundary. Single crystal refinement was performed successfully with the twinning model. A similar analysis was extended to the structures of Sr2Be2B2O7 and AEAl2B2O7 (AE = Ca, Sr or Ba).

Re-Examination of the Crystal Structure of Na2Al2B2O7 - Stacking Faults and Twinning. M.He, L.Kienle, A.Simon, X.L.Chen, V.Duppel: Journal of Solid State Chemistry, 2004, 177[9], 3212-8