Surface and bulk conduction and thermodynamic properties of ionic salt CsH5(PO4)2

Transport properties of ionic salt CsH5(PO4)(2) are studied by the impedance method. The salt's bulk conductivity ranges from 10(-8) to 10(-4) S cm(-1) in the temperature interval 90 to 145 degrees C. The apparent activation energy is high (1.6-2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (similar to 5.6 and 1 times x 10(-6) S cm(-1), respectively, at 130 degrees C. The conductivity of polycrystalline samples is higher by 1-2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt's thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6 degrees C), with the melting enthalpy equal to similar to 34 kJ mol(-1). The crystallization occurs at lower temperatures (107 degrees C) and the crystallization enthalpy (-18 kJ mol(-1)) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.