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 shift at a faster rate compared to the II → II 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 III ⇋ II transition region is studied.