The calcite-like form of potassium nitrate, KNO3, decomposed under the transmission electron microscope to form KNO2 which subsequently decomposed giving the high-temperature β form of K2O. Two closely related orientation relations were observed for KNO2. Referred to the four-molecule cell of KNO3, they were NNO3∥KNO2, (011)KNO3∥(011)KNO2; and KNO3∥KNO2, (001)KNO3∥(001)KNO2. These and a different published orientation relation for the decomposition of cadmium carbonate conform, respectively, to orientations resulting from a corresponding structural phase transformation in rubidium nitrate. β-K2O formed with its cube axes parallel to those of KNO2. Both nitrate and carbonate reactions can be regarded as topotaxial. Application of the crystallographic approach to orientations and accommodation of misregistry is discussed.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry