Central peaks due to microdomains, impurities or…?

Although in 1969 certain structural phase transitions were predicted to have a so‐called “central peak,” the experimental observations of the phenomenon show it to be more widespread than originally predicted. By now central peaks have been found in insulators, metals, materials with high transition temperatures, materials with low transition temperatures, materials that undergo acoustic‐mode instabilities and materials that undergo optical‐mode instabilities. A variety of theoretical explanations have been offered recently, including a picture involving microdomains or solitons and an alternative picture involving impurities. As James Krumhansl, a proponent of microdomains told us, “The explanation has not yet been wrapped up and put on the shelf.”