Rb5H7(PO4)4 as a new example of the superprotonic conductor
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Thermal and transport properties, as well as spectral characteristics of Rb5H7(PO4)4, have been investigated by several methods. It was shown that Rb5H7(PO4)4 undergoes a reversible phase transition at Tp ~ 237 °С. However, the interval of the high-temperature phase stability is quite narrow, about 15 °С. The initial dehydration event in Rb5H7(PO4)4 occurs at 200 °С. The conductivity measurements were performed under highly humidified conditions (PH2O ≈ 0.56 atm.) to suppress dehydration of the title salt. The phase transition leads to the sharp increase of proton conductivity up to 10−2 S/cm. The reverse transition goes slowly with significant hysteresis on cooling. Thus, the superprotonic conductivity of Rb5H7(PO4)4 was determined. The possibility of superionic phase stabilization by humidification was shown. The IR- and Raman spectra have been recorded at room temperature and discussed in relation to the crystal structure.
KeywordsRb5H7(PO4)4 Proton conductivity Ac-impedance spectroscopy Superprotonic conductors Thermal analysis
The authors thank their colleagues Dr. N.V. Bulina, Dr. K.B. Gerasimov, Dr. E.A. Losev, Dr. A.A. Matvienko for the help in the performance of experiments on X-ray powder diffraction, differential scanning calorimetry, IR-spectroscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy. This research was carried out within the State Assignment to ISSCM SB RAS (project 0301-2018-0002).
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Conflict of interest
The authors declare that they have no conflict of interest.
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