Examination of the superprotonic transition and dehydration behavior of Cs 0.75Rb 0.25H 2PO 4 by thermogravimetric and differential thermal analyses

Abstract

The dehydration and the superprotonic transition behavior of Cs 0.75Rb 0.25H 2PO 4 have been investigated via thermogravimetry and differential thermal analysis. To enable measurements under the high water partial pressures required, a high humidity system ( p H 2O = 0.02–0.8 atm) capable of weight change detection at 0.7% resolution and thermal events with 0.01 °C resolution was assembled. It has been found that the superprotonic phase transition temperature of Cs 0.75Rb 0.25H 2PO 4 is 231 °C, slightly higher than that of CsH 2PO 4. In contrast, dehydration of Cs 0.75Rb 0.25H 2PO 4 under p H 2O = 0.35 atm occurs at 265 °C, a somewhat lower temperature than that at which CsH 2PO 4 undergoes dehydration. Analysis of the temporal evolution of both transformations suggests a mechanism of continuous nucleation of the high temperature phase at a constant nucleation rate combined with three-dimensional growth.