The influence of Cs₂HPO₄·H₂O impurity on the proton conductivity and thermal properties of CsH₂PO₄

The electrotransport, structural and thermodynamic properties of CsH₂PO₄ with small amount of Cs₂HPO₄·2H₂O (mole fraction, x = 0.01–0.1) has been investigated by the impedance, IR spectroscopy, X-ray diffraction and differential scanning calorimetric methods. The addition of Cs₂HPO₄·2H₂O up to mole fraction x ≤ 0.03 was shown to increase markedly the low-temperature conductivity and change the thermodynamic characteristics of cesium dihydrogen phosphate. The low-temperature conductivity enhances up to σ_150°C ~2 · 10⁻³ S·cm⁻¹ for x = 0.1 and the activation energy of conductivity decreases to E_a = 0.56 eV. The superionic phase transition becomes more diffusive and almost disappears at x = 0.1. The high-temperature conductivity doesn't change significantly at the doping of CsH₂PO₄ up to x = 0.1. While the small deviation of proton content in CsH₂PO₄ shows a weak effect for XRD and IR spectroscopy. According to X-ray diffraction patterns the Cs_1+xH_2−xPO₄ solid solutions were not observed and the formation of (1-2x)CsH₂PO₄-xCs₃(H_1.5PO₄)₂ composites took place. The effect of the deficiency of protons on the conductivity of CsH₂PO₄ in the low humidity conditions was discovered firstly and is of scientific and practice importance.