Overview of the origin of tweed texture

An overview is given of the origin of tweed texture in the context of structural phase transitions. The texture is observed in a wide range of materials in cooling through the transition temperature T-c. Its origin is shown by theory and computer simulation to lie in the ease of formation of particular domain (twin) boundaries in the case of transformations satisfying certain conditions. The material is in fact already a dense mass of embryos of the ordered phase, present as thermodynamic fluctuations at temperatures well above T-c. These fluctuations control the length and width of the tweed microdomains observed after quenching. Further coarsening of the tweed towards a stripe texture proceeds via the creation of needle domains governed by the strains around right-angled domain walls.