Disclinations, first observed in mesomorphic phases, are relevant to a number of ill-ordered condensed matter media, with continuous symmetries or frustrated order. They also appear in polycrystals at the edges of grain boundaries. They are of limited interest in solid single crystals, where, owing to their large elastic stresses, they mostly appear in close pairs of opposite signs. The relaxation mechanisms associated with a disclination in its creation, motion, change of shape, involve an interplay with continuous or quantized dislocations and/or continuous disclinations. These are attached to the disclinations or are akin to Nye's dislocation densities, well suited here. The notion of 'extended Volterra process' takes these relaxation processes into account and covers different situations where this interplay takes place. These concepts are illustrated by applications in amorphous solids, mesomorphic phases and frustrated media in their curved habit space. The powerful topological theory of line defects only considers defects stable against relaxation processes compatible with the structure considered. It can be seen as a simplified case of the approach considered here, well suited for media of high plasticity or/and complex structures. Topological stability cannot guarantee energetic stability and sometimes cannot distinguish finer details of structure of defects.
Helix alignment, chevrons, and edge dislocations in twist-bend ferroelectric nematics
Advanced Materials and Liquid Crystal Institute, Kent State University（肯特州立大学先进材料与液晶研究所）；Materials Science Graduate Program, Kent State University（肯特州立大学材料科学研究生项目）；Faculty of Chemistry, University of Warsaw（华沙大学化学系）；Faculty of Advanced Technology and Chemistry, Military University of Technology（军事理工大学先进技术与化学学院）；Jozef Stefan Institute（约瑟夫斯蒂芬研究所）；Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor（马里博尔大学自然科学与数学学院物理系）；Department of Physics, Kent State University（肯特州立大学物理系）
