It was recalled that the X-ray diffraction patterns from nominally β-phase specimens often differed from those which were expected for a cubic crystal structure. These differences included the presence of additional peaks, enhanced background intensities, peak-broadening, changes in relative peak heights, and shifts in peak positions. The discrepancy had long been recognized as being due to the presence of stacking faults. Computer simulations were used here to showed that the variations were closely related to differences in the types and spatial distributions of stacking faults. In these simulations, stacking sequences were generated by using a selectively activated 1-dimensional Ising model which permitted a wide variety of fault configurations to be generated. The simulation results showed that it was necessary to suppress 2-layer twins, but to promote the formation of 3-layer twins, so as to reproduce the gradual increase in background intensity which was observed experimentally. The greatest puzzle which was associated with the present strategy for generating model stacking sequences was the need for a so-called switch which would produce a bimodal distribution of stacking errors.

V.V.Pujar, J.D.Cawley: Journal of the American Ceramic Society, 1997, 80[7], 1653-62