Acta Crystallographica Section B

Structural Science

Volume 55, Part 4 (August 1999)

research papers

Acta Cryst. (1999). B55, 507-516 [ doi:10.1107/S0108768199003845 ]

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)

T. Kogure and M. Nespolo

Abstract: In this study it is shown that the stacking sequences in long-period mica polytypes (including a rare example of a mixed-rotation polytype, with a 36-layer long periodicity) can be unambiguously determined using atomic resolution images recorded down two zone axes separated by 30° (e.g. [100] and [310]) at the same area. Uniformity of these stacking sequences in a large area is further confirmed by the correspondence between computed and observed Periodic Intensity Distributions (PIDs) in electron diffraction patterns. The appearance of long-period polytypes containing layers with different orientation parity may be explained by the coalescence of two small crystals during crystal growth.

Keywords: Mica polytypes; Transmission electron microscopy; Oxybiotite; Periodic intensity distribution.