, Volume 25, Issue 2, pp 551–557 | Cite as

Rb5H7(PO4)4 as a new example of the superprotonic conductor

  • Anna A. GaydamakaEmail author
  • Valentina G. Ponomareva
  • Irina N. Bagryantseva
Original Paper


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.


Rb5H7(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).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


  1. 1.
    Baranov AI (2003) Crystals with disordered hydrogen-bond networks and superprotonic conductivity. Rev Crystallogr Rep 48:1012–1037CrossRefGoogle Scholar
  2. 2.
    Ivanov-Shitz AK, Murin A (2010) Solid State Ionic, vol 2. SPb University Press, St. PetersburgGoogle Scholar
  3. 3.
    Haile SM, Chisholm CRI, Sasaki K, Boysen DA, Uda T (2007) Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes. Faraday Discuss 134:17–39. CrossRefGoogle Scholar
  4. 4.
    Qing G, Kikuchi R, Takagaki A, Sugawara T, Oyama ST (2015) CsH2PO4/epoxy composite electrolytes for intermediate temperature fuel cells. Electrochim Acta 169:219–226. CrossRefGoogle Scholar
  5. 5.
    Uda T, Haile SM (2005) Thin-membrane solid-acid fuel cell. Electrochem Solid-State Lett 8:A245–A246. CrossRefGoogle Scholar
  6. 6.
    Boysen DA, Chisholm CRI, Haile SM, Narayanan SR (2000) Polymer solid acid composite membranes for fuel-cell applications. J Electrochem Soc 147:3610. CrossRefGoogle Scholar
  7. 7.
    Baranov AI, Khiznichenko VP, Sandur VA, Shuvalov LA (1988) Frequency dielectric dispersion in the ferroelectric and superionic phases of CsH2PO4. Ferroelectrics 81:183–186. CrossRefGoogle Scholar
  8. 8.
    Baranov AI, Khiznichenko VP, Shuvalov LA (1989) High temperature phase transitions and proton conductivity in some KDP-family crystals. Ferroelectrics 100:135–141CrossRefGoogle Scholar
  9. 9.
    Taninouchi YK, Uda T, Awakura Y, Ikeda A, Haile SM (2007) Dehydration behavior of the superprotonic conductor CsH2PO4 at moderate temperatures: 230 to 260 °C. J Mater Chem 17:3182–3189. CrossRefGoogle Scholar
  10. 10.
    Otomo J, Minagawa N, Wen CJ et al (2003) Protonic conduction of CsH2PO4 and its composite with silica in dry and humid atmospheres. Solid State Ionics 156:357–369. CrossRefGoogle Scholar
  11. 11.
    Li Z, Tang T (2010) High-temperature dehydration behavior and protonic conductivity of RbH2PO4 in a humid atmosphere. Mater Res Bull 45:1909–1915. CrossRefGoogle Scholar
  12. 12.
    Li Z (2010) Impedance analysis and protonic conduction mechanism in RbH2PO4/SiO2 composite systems. Electrochim Acta 55:7298–7304. CrossRefGoogle Scholar
  13. 13.
    Boysen DA, Haile SM, Liu H, Secco RA (2004) Conductivity of potassium and rubidium dihydrogen phosphates at high temperature and pressure. Chem Mater 16:693–697. CrossRefGoogle Scholar
  14. 14.
    Botez CE, Tackett RJ, Hermosillo JD, Zhang J, Zhao Y, Wang L (2012) High pressure synchrotron x-ray diffraction studies of superprotonic transitions in phosphate solid acids. Solid State Ionics 213:58–62. CrossRefGoogle Scholar
  15. 15.
    Prince BYE, Takagi S, Mathew M, Brown WE (1984) The structure of dicalcium potassium heptahydrogen tetrakis (phosphate) dihydrate, Ca2KH7(PO4)4∙2H2O, by X-ray and neutron diffraction. Acta Cryst 2:1499–1502Google Scholar
  16. 16.
    Mathew M, Brown WE (1980) Phosphate ion with three “symmetric” hydrogen bonds: the structure of Ca2(NH4)H7(PO4)4 2H2O. Acta Crystallogr Sect B 36:766–771CrossRefGoogle Scholar
  17. 17.
    Averbuch-Pouchot MT, Durif A (1985) Structure of pentarubidium heptahydrogen tetrakis (phosphate). Acta Cryst C41:1555–1556Google Scholar
  18. 18.
    Ratajczak H, Mielke Z (1968) Internal fundamental vibrations of RbH2PO4 and its deuterated analogue in the non-ferroelectric phase. J Mol Struct 1:397–401CrossRefGoogle Scholar
  19. 19.
    Baran J, Lis T, Ratajczak H (1989) Structure and polarized IR spectra of the K2HPO4·3H2O crystal. J Mol Struct 195:159–174. CrossRefGoogle Scholar
  20. 20.
    Sheludyakova LA, Afanasieva VA, Podberezskaya NV, Mironov YI (1999) Spectral and structural analysis of sodium hydrophosphates and hydroarsenates. Russ J Struct Chem 40:869–872CrossRefGoogle Scholar
  21. 21.
    Ichikawa M (1978) The O–H vs O.O distance correlation, the geometric isotope effect in OHO bonds, and its application to symmetric bonds. Acta Crystallogr Sect B: Struct Crystallogr Cryst Chem 34:2074–2080. CrossRefGoogle Scholar
  22. 22.
    Baur WH (1974) The geometry of polyhedral distortions. Predictive relationships for the phosphate group. Acta Crystallogr Sect B: Struct Crystallogr Cryst Chem 30:1195–1215. CrossRefGoogle Scholar
  23. 23.
    Romain F, Novak A (1991) Raman study of the high-temperature phase transition in CsH2PO4. J Mol Struct 263:69–74CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Anna A. Gaydamaka
    • 1
    • 2
    Email author
  • Valentina G. Ponomareva
    • 1
    • 2
  • Irina N. Bagryantseva
    • 1
    • 2
  1. 1.Institute of Solid State Chemistry and MechanochemistrySiberian Branch of the Russian Academy of SciencesNovosibirskRussia
  2. 2.Novosibirsk State UniversityNovosibirskRussia

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