Phase Transformations of Rubidium Nitrate and Its Solid Solutions with Cesium and Potassium Nitrates

Abstract

The four solid-solid phase transformations in the cooled melts of RbNO₃ and its solid solutions, Cs_xRb_1−xNO₃, and K_xRb_1−xNO₃ are examined by electrical conductivity measurement, differential thermal analysis (DTA), dilatometry and X-ray diffraction technique. The solubility of CsNO₃ of KNO₃ in RbNO₃ is explained on the basis of similarity of phases of RbNO₃ with those of CsNO₃ or KNO₃. With increasing x, in the systems Cs_xRb_1−xNO₃ and K_xRb_1−xNO₃, the transition temperature IV→III remains nearly unaffected whereas the III→II shifts at a faster rate compared to the II→I transition. This is interpreted in terms of (i) the crystallography of different phase of RbNO₃ and (ii) the variation of the cation to anion radius ratio with x in the solid solutins. Coexistence of phases III and II in the (Remark: Graphics omitted.) transition region is studied.