High-temperature phase transitions in cesium dihydrogen phosphate under ambient and high-pressure conditions: A synchrotron x-ray diffraction study
Temperature- and time-resolved synchrotron X-ray powder diffraction has been used to study the structural and chemical modifications that accompany the sharp 1000-fold increase in the proton conductivity of CsH2PO 4 at high temperatures. Data collected upon heating on samples kept under ambient pressure evidence a polymorphic structural transition (monoclinic→cubic) at 237°C followed by a slow and partial thermal decomposition of the cubic CsH2PO4 phase. The thermal decomposition can be suppressed by carrying out the measurements under high pressure (∼1GPa), which leads to the transformation of the low-temperature monoclinic CsH2PO 4 into a single, thermally stable cubic CsH2PO4 phase at a temperature within the 255-275°C range. The space group and lattice parameters of the cubic phases observed under ambient- and high-pressure conditions are identical. Since a jump in the proton conductivity of the title compound has also been observed under both ambient- and high-pressure conditions (at ∼230°C and 260°C respectively), we conclude that the superprotonic behavior of CsH2PO4 is associated with a polymorphic structural transition and not with chemical modifications.
Hermosillo, Juan Daniel, "High-temperature phase transitions in cesium dihydrogen phosphate under ambient and high-pressure conditions: A synchrotron x-ray diffraction study" (2006). ETD Collection for University of Texas, El Paso. AAI1439486.