A TEM study of long-period mica polytypes: determination of the stacking sequence of oxybiotite by means of atomic resolution images and Periodic Intensity Distribution (PID)

In this study it is shown that the stacking sequences in long-period mica p olytypes (including a rare example of a mixed-rotation polytype, with a 36- layer long periodicity) can be unambiguously determined using atomic resolu tion images recorded down two zone axes separated by 30 degrees (e.g. [100] and [3 (1) over bar 0]) at the same area. Uniformity of these stacking seq uences in a large area is further confirmed by the correspondence between c omputed and observed Periodic Intensity Distributions (PIDs) in electron di ffraction patterns. The appearance of long-period polytypes containing laye rs with different orientation parity may be explained by the coalescence of two small crystals during crystal growth.