STRUCTURAL STUDY OF THE SMECTIC-C TWIST GRAIN-BOUNDARY PHASE

We report the first three dimensional x-ray study of the recently discovered twist grain boundary smectic- C phase (TGBC). Unlike the predictions of the original Renn-Lubensky model for TGB phases (and the experimental observations in the untilted TGBA phase), the smectic layers in the TGBC phase are shown to be tilted with respect to the helical TGB axis by an angle approximately equal to the smectic- C director tilt angle. The reciprocal lattice consists of either two rings of equispaced Bragg spots or uniform rings confirming the existence of both commensurate and incommensurate TGB phases. © 1995 The American Physical Society.