Europhys. Lett.
Volume 72, Number 6, December 2005
Page(s) 976 - 982
Section Condensed matter: structural, mechanical and thermal properties
Published online 23 November 2005
Europhys. Lett., 72 (6), pp. 976-982 (2005)
DOI: 10.1209/epl/i2005-10336-3

Biaxiality and temperature dependence of $\mth{3}$- and $\mth{4}$-layer intermediate smectic-phase structures as revealed by resonant $\mth{\rm X}$-ray scattering

N. W. Roberts1, S. Jaradat1, L. S. Hirst1, 2, M. S. Thurlow1, Y. Wang1, S. T. Wang3, Z. Q. Liu3, C. C. Huang3, J. Bai4, R. Pindak4 and H. F. Gleeson1

1  School of Physics and Astronomy, University of Manchester Manchester, M13 1PL, UK
2  Department of Physics, Florida State University Tallahassee, FL 32306-4350, USA
3  School of Physics and Astronomy, University of Minnesota Minneapolis, MN 55455, USA
4  Brookhaven National Lab, NSLS - Upton, NY 11973, USA

received 19 August 2005; accepted in final form 19 October 2005
published online 23 November 2005

High-resolution resonant X-ray diffraction experiments have been performed on free-standing films of two selenium-containing antiferroelectric liquid-crystal mixtures. Optical studies had indicated that both mixtures exhibit exceptionally wide intermediate phases, over a total range of $>9\un{K}$. Through the structural information obtained from the resonant scattering data, we confirm that the intermediate phases of these mixtures show both 3-layer and 4-layer structural periodicities. Moreover, due to the stability of these phases, we report for the first time the temperature dependence of both the helicoidal pitch and distortion angle in the 3-layer phases deduced using the resonant X-ray technique. Analysis using an extension of the theory set out by Levelut and Pansu (LEVELUT A-M. and PANSU B., Phys. Rev. E, 60 (1999) 6803) shows that over the temperature ranges measured, the pitch changes linearly as a function of temperature whilst the distortion angle remains constant.

61.30.Eb - Experimental determinations of smectic, nematic, cholesteric, and other structures.
78.70.Ck - X-ray scattering.
83.80.Xz - Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

© EDP Sciences 2005