Chapter

Introduction to twinning

Simon Parsons

in Crystal Structure Analysis

Second edition

Published in print June 2009 | ISBN: 9780199219469
Published online September 2009 | e-ISBN: 9780191722516 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199219469.003.0018

Series: International Union of Crystallography Texts on Crystallography

Introduction to twinning

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This chapter presents a simple model for twinning, the occurrence of more than one orientation of a structure with a rational relationship in a crystal. Characterization of a two-component twin requires a twin law and a twin fraction; common examples of twin laws are discussed, together with possible extension to multiple twins. Twinning affects diffraction patterns in various ways, with full or partial overlap of some or all reflections from the twin components. Different types of twinning include inversion, merohedral, pseudo-merohedral (overlap of all reflections), and non-merohedral (some overlap). Methods of handling twins in practice are described, including how to derive the twin law, some common signs of twinning, and detailed applications in a number of examples.

Keywords: twinning; twin law; twin fraction; inversion twin; merohedral twin; pseudo-merohedral twin; non-merohedral twin

Chapter.  11385 words.  Illustrated.

Subjects: Crystallography

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