Systematic Water Uptake Energetics of Yttrium-Doped Barium Zirconate—A High Resolution Thermochemical Study
2020
Gonçalves, Mayra D. | Mielewczyk-Gryń, Aleksandra | Maram, Pardha S. | Kryścio, Łukasz | Gazda, Maria | Navrotsky, Alexandra
A combination of surface area analyzer and microcalorimetry was employed to investigate the in situ water uptake energetics and the mechanism of proton incorporation in yttrium-doped barium zirconate in the temperature range 200–400 °C. The BaZr₁–ₓYₓO₃ solid solutions are made with variable yttrium content (x = 10, 20, and 30 mol %) by a controlled oxidant-peroxo synthesis method. The water uptake increases as the partial pressure of water increases; however, no saturation in the hydration isotherm is observed, implying further reaction at higher pH₂O. The results suggest three distinct regions of hydration energies as a function of water content. The first water uptake enthalpy values showed high exothermicity, −140, −158, and −157 kJ mol–¹ for BaZr₁–ₓYₓO₃ (x = 10, 20, and 30 mol %), respectively, at 400 °C, and the strong exothermic contribution supports the dissociative incorporation of water. The stepwise in situ hydration energetics is essential to understand the mechanisms of water incorporation and the role of H₂O uptake in transport properties.
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