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A group of multi-component oxides based on BaZrO ₃ have been prepared using a solid-state reaction method and examined in terms of their water uptake and thermodynamics of formation.

This study concerns energetics of formation and the stability in high water partial pressure of BaLnCo ₂ O _{6− δ} , (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd _{1− x} La _x Co ₂ O _{6− δ} , where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites.

High entropy oxides are emerging as an exciting new avenue to design highly tailored functional behaviors that have no traditional counterparts. Study and application of these materials are bringing together scientists and engineers from physics, chemistry, and materials science. The diversity of each of these disciplines comes with perspectives and jargon that may be confusing to those outside of the individual fields, which can result in miscommunication of important aspects of research. In this Perspective, we provide examples of research and characterization taken from these different fields to provide a framework for classifying the differences between compositionally complex oxides, highmore » entropy oxides, and entropy stabilized oxides, which is intended to bring a common language to this emerging area. We highlight the critical importance of understanding a material’s crystallinity, composition, and mixing length scales in determining its true definition.« less

The defect fluorite yttrium niobate Y₃NbO₇ and pyrochlore yttrium titanate Y₂Ti₂O₇ solid solutions have been synthesized via a solid state synthesis route. The resulting stoichiometry of the oxides is Y_2+xTi_2-2xNb_xO₇, where x = 0 to x = 1. All of the samples were single-phase; however, for those with a predominant fluorite phase, a small amount of additional pyrochlore phase was detected. The volume of the solid solution unit cells linearly increases with increase in yttrium niobate content. The water uptake increases with (x) and the protonic defect concentration reaches almost 4.5 × 10^-3 mol mol^-1 at 300 °C. The calculatedmore » enthalpy of formation from oxides suggests strong stability for all of the compositions, with the values of enthalpy ranging from -84.6 to -114.3 kJ mol^-1. The total conductivity does not have a visible dependence on Y₃NbO₇ content. For each compound, the total conductivity is higher in wet air. Interestingly, for samples where x < 0.5, the ratio of conductivity in hydrogen to air increases with increasing temperature, while for x > 0.5, the trend is the opposite.« less

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. Themore » 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.« less