Proton and Oxygen-Ion Conductivities of Hexagonal Perovskite Ba5In2Al2ZrO13

The hexagonal perovskite Ba5In2Al2ZrO13 and In3+-doped phase Ba5In2.1Al2Zr0.9O12.95 were prepared by the solid-state synthesis method. The introduction of indium in the Zr-sublattice was accompanied by an increase in the unit cell parameters: a = 5.967 angstrom, c = 24.006 angstrom vs. a = 5.970 angstrom, c = 24.011 angstrom for doped phase (space group of P6(3)/mmc). Both phases were capable of incorporating water from the gas phase. The ability of water incorporation was due to the presence of oxygen deficient blocks in the structure, and due to the introduction of oxygen vacancies during doping. According to thermogravimetric (TG) measurements the compositions of the hydrated samples corresponded to Ba5In2Al2ZrO12.7(OH)(0.6) and Ba5In2.1Al2Zr0.9O12.54(OH)(0.82). The presence of different types of OH--groups in the structure, which participate in different hydrogen bonds, was confirmed by infrared (IR) investigations. The measurements of bulk conductivity by the impedance spectroscopy method showed that In3+-doping led to an increase in conductivity by 0.5 order of magnitude in wet air (pH(2)O = 1.92.10(-2) atm); in this case, the activation energies decreased from 0.27 to 0.19 eV. The conductivity-pO(2) measurements showed that both the phases were dominant proton conductors at T < 500 degrees C in wet conditions. The composition Ba5In2.1Al2Zr0.9O12.95 exhibited a proton conductivity similar to 10(-4) S.cm(-1) at 500 degrees C. The analysis of partial (O2-, H+, h(center dot)) conductivities of the investigated phases has been carried out. Both phases in dry air (pH(2)O = 3.5.10(-5) atm) showed a mixed (oxygen-ion and hole) type of conductivity. The obtained results indicated that the investigated phases of Ba5In2Al2ZrO13 and Ba5In2.1Al2Zr0.9O12.95 might be promising proton-conducting oxides in the future applications in electrochemical devices, such as solid oxide fuel cells. Further modification of the composition and search for the optimal dopant concentrations can improve the H+-conductivity.

Automated summary

The hexagonal perovskite Ba5In2Al2ZrO13 and In3+-doped phase Ba5In2.1Al2Zr0.9O12.95 were synthesized by solid-state synthesis. Both phases were capable of incorporating water due to the presence of oxygen deficient blocks and oxygen vacancies caused by doping. Infrared investigations confirmed the presence of different types of OH--groups in the structure. Impedance spectroscopy showed that In3+-doping increased conductivity by 0.5 order of magnitude in wet air. Both phases were dominant proton conductors at temperatures below 500 °C in wet conditions. The composition Ba5In2.1Al2Zr0.9O12.95 exhibited a proton conductivity of approximately 10(-4) S.cm(-1) at 500 °C.