Proton and Oxygen-Ion Conductivities of Hexagonal Perovskite Ba5In2Al2ZrO13

Abstract

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 Å, c = 24.006 Å vs. a = 5.970 Å, c = 24.011 Å for doped phase (space group of P63/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 (pH2O = 1.92·10−2 atm); in this case, the activation energies decreased from 0.27 to 0.19 eV. The conductivity−pO2 measurements showed that both the phases were dominant proton conductors at T < 500 °C in wet conditions. The composition Ba5In2.1Al2Zr0.9O12.95 exhibited a proton conductivity ~10−4 S·cm−1 at 500 °C. The analysis of partial (O2−, H+, h•) conductivities of the investigated phases has been carried out. Both phases in dry air (pH2O = 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.

Novel Nb5+-doped hexagonal perovskite Ba5In2Al2ZrO13 (structure, hydration, electrical conductivity)

“…Figure 1 demonstrates X-ray diffraction patterns (XRD) of the powder Nb-doped phase Ba5In2Al2Zr0.9Nb0.1O13.05 in comparison with previously obtained undoped sample Ba5In2Al2ZrO13 and In-doped phase Ba5In2Al2Zr0.9In0.1O12.95 [20]. It is seen that all the diffractograms have a similar shape.…”

“…The hydration processes, the nature of oxygen-hydrogen groups and proton transport were examined for the first time. The discussion of the obtained results was carried out in comparison with the previously obtained data for the phases Ba5In2Al2ZrO13 and Ba5In2.1Al2Zr0.9O12.95 [20].…”

“…Oxygen partial pressure dependences of electric conductivity for Ba5In2Al2ZrO13 [20], Ba5In2Al2Zr0.9In0.1O12.95 [20], Ba5In2Al2Zr0.9Nb0.1O13.05 in dry and wet atmospheres in comparison are shown in Figure 8. The general view of the dependences for all the compounds is similar.…”

“…Another hexagonal perovskite Ba5In2Al2ZrO13 has also recently been described as being capable of exhibiting proton transport [20]. The structure of this compound can be considered as a result of the intergrowth of oxygendeficient Ba2InAlO5-blocks and BaZrO3-blocks [21].…”

“…The structure of this compound can be considered as a result of the intergrowth of oxygendeficient Ba2InAlO5-blocks and BaZrO3-blocks [21]. Acceptor doping of this phase by introduction of In 3+ in the Zr 4+ -sublattice was accompanied by some increase in proton conductivity [20], but the increase was small. In this regard, other types of doping, such as donor doping, may be of interest.…”