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A group of multi-component oxides based on BaZrO₃ have been prepared using a solid-state reaction method and examined in terms of their water uptake and thermodynamics of formation. Depending on the type and amount of acceptor substitution, the synthesized compounds exhibit various proton defect concentrations, reaching up to 0.2 mol/mol for a compound containing 10 different elements in the B-sublattice, where 50% of them are acceptors. Further, for the most promising materials, van’t Hoff plots were created and the enthalpies and entropies of hydration were calculated. At higher temperatures, these parameters do not differ from the values for the referencemore » yttrium doped barium zirconate. However, at lower temperatures they are more negative, indicating a more exothermic process of proton incorporation.« less

Surface energetics of zinc sulfide nanoparticles determines their structure, properties, and occurrence. Using a combination of experimental techniques, we investigated the thermodynamics of the two polymorphs, sphalerite and wurtzite at bulk and nanoscale to understand their occurrence. Calorimetric measurements confirmed that wurtzite has a lower surface energy than sphalerite, which causes a reversal in phase stability at the nanoscale, with wurtzite energetically stable for particle size below 10 nm. Taking these surface energies into account, a simple model of the thermodynamics of the sphalerite - wurtzite transformation as a function of particle size and temperature can explain the occurrence ofmore » the zinc sulfide polymorphs in environments as diverse as ore bodies and planetary atmospheres.« 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