Defect Chemistry of Yttrium-Doped Barium Zirconate: A Thermodynamic Analysis of Water Uptake

Abstract

Thermogravimetry has been used to evaluate the equilibrium constants of the water incorporation reaction in yttrium-doped BaZrO 3 with 20-40% yttrium in the temperature range 50-1000 °C under a water partial pressure of 0.023 atm. The constants, calculated under the assumption of a negligible hole concentration, were found to be linear in the Arrhenius representation only at low temperatures (e500 °C). Nonlinearity at high temperatures is attributed to the occurrence of electronic defects. The hydration enthalpies determined here range from -22 to -26 kJ mol -1 and are substantially smaller in magnitude than those reported previously. The difference is a direct result of the different temperature ranges employed, where previous studies have utilized higher temperature thermogravimetric measurements, despite the inapplicability of the assumption of a negligible hole concentration. The hydration entropies measured in this work, around -40 J K -1 mol -1 , are similarly smaller in magnitude than those previously reported and are considerably smaller than what would be expected from the complete loss of entropy of vapor-phase H 2 O upon dissolution. This result suggests that substantial entropy is introduced into the oxide as a consequence of the hydration. The hydration reaction constants are largely independent of yttrium concentration, in agreement with earlier reports.

Properties and applications of perovskite proton conductors

“…Thereby, as a consequence of a physical artifact, ΔH H 2 O and ΔS H 2 O extracted from the curve may present inconsistent values in a wide temperature range. Not surprisingly, the resulting hydration entropies and enthalpies from 50-500 °C (-22 to -26 kJ/mol and -39 to -44 J/K.mol, respectively) of yttrium doped barium zirconate found by Yamazaki et al 52 were smaller in magnitude than those reported in the literature. As an example, at higher temperature range, 550-900 °C, the values of ΔH H 2 O and ΔS H 2 O reported by Kreuer et al 54 were -93.3 kJ/mol and -103.2 J/K.…”

Proton conductivity of columnar ceria thin-films grown by chemical vapor deposition

“…19 Over a small change in proton concentration (the variation in conductivity recorded here is only about 10%) and under the approximation of ideal solution behavior, eqn (1) implies that the proton resistivity (inversely proportional to concentration) should display a power law factor of À B108 nm). 20 There are many factors that could explain a deviation from a power law factor of À 1 2 in undoped ceria even for bulk proton uptake, first amongst these being the low intrinsic oxygen vacancy concentration such that the effects of site saturation cannot be neglected.…”

Effect of synthesis atmosphere on the proton conductivity of Y-doped barium zirconate solid electrolytes

“…Sol-gel, polyacrylamide, combustion, coprecipitation are synthesis methods used to produce BZY powders with high sinterability to obtain dense compacts after sintering [16,18,[20][21][22][23]. The main advantage of the OPM over other methods is that it leaves no residues [33,34], which could otherwise promote deleterious effects on the proton conductivity.…”

“…Very recently, BZY protonic ceramic fuel cells with high power output have been reported using BZY solid electrolytes sintered with CuO sintering aid [19]. Wet-chemical routes have already been used to produce powder particles with higher sinterability to obtain pellets sintered at relatively low temperatures [16,18,[20][21][22][23][24]. A total proton conductivity of $0.01 S/cm at 450°C in a polycrystalline BZY20 sample produced by a sol-gel route was reported.…”