The persistence of crystal axes in a thermal transformation

Abstract

Abstract X -ray measurements on single crystals of KNO3 are described which test how far the crystal axespersist in a thermal transformation cycle I →128°←II. Though some break-up into disoriented subunits is observed, pseudo-single crystals are generally obtained after a thermal cycle. In moist crystals, the b-axis shows a marked persistence with respect to the original b-axis. The a- and c-axes often, but not always, undergo rotation about the original direction of the b-axis. The direction of none of the original axes persists in rigorously dried crystals. The observations are discussed with reference to geometric and thermodynamic aspects of the transformation.