Proton Conductivity and Thermal Properties of Ba(H{sub 2}PO{sub 4}){sub 2}

• Published in: Inorganic materials 2018-04, Vol.54 (4)
• Main Authors: Bagryantseva, I. N., Ponomareva, V. G.
• Format: Article
• Language: English
• Subjects: ACTIVATION ENERGY; ANISOTROPY; BARIUM PHOSPHATES; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CONTROLLED ATMOSPHERES; CRYSTAL GROWTH; CRYSTALLOGRAPHY; DEHYDRATION; ENTHALPY; MONOCRYSTALS; ORTHORHOMBIC LATTICES; PHASE TRANSFORMATIONS; POLYCRYSTALS; PROTON CONDUCTIVITY; PYROLYSIS; PYROPHOSPHATES; SPECTROSCOPY; WATER
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168518040027

We have grown single crystals of barium dihydrogen phosphate and studied its thermal transformations during heating to 500°C and its electrotransport properties. Ba(H{sub 2}PO{sub 4}){sub 2} (Pccn) has been shown to undergo no phase transitions up to its dehydration temperature. The thermal decomposition of Ba(H{sub 2}PO{sub 4}){sub 2}, accompanied by dehydration, involves two steps, with maximum rates at ~265 and 370°C, and results in the formation of barium dihydrogen pyrophosphate and barium metaphosphate, respectively. The total enthalpy of the endothermic dehydration events is–244.6 J/g. Using impedance spectroscopy, we have studied in detail the proton conductivity of polycrystalline and single-crystal Ba(H{sub 2}PO{sub 4}){sub 2} samples in a controlled atmosphere. Adsorbed water has been shown to have a significant effect on the proton conductivity of Ba(H{sub 2}PO{sub 4}){sub 2} up to 130°C. The proton conductivity of the Ba(H{sub 2}PO{sub 4}){sub 2} single crystals has been shown to be anisotropic. The conductivity anisotropy correlates with specific structural features of the salt. Higher conductivity values, 3 × 10{sup –9} to 2 × 10{sup –7} S/cm in the range 60–160°C, have been observed in the [100] crystallographic direction, exceeding the conductivity along [010] by an order of magnitude. The activation energy for proton conduction is 0.80 eV.