Thermodynamics of BaCa(1 + y)/3Nb(2 − y)/3O3 − δ·xH2O proton-conducting perovskites
| Autor: | Dmitry Malyshkin, A. Yu. Zuev, I.L. Ivanov, Vladimir V. Sereda, Dmitry S. Tsvetkov, Anton L. Sednev-Lugovets |
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| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Journal of Thermal Analysis and Calorimetry. 142:1989-2001 |
| ISSN: | 1588-2926 1388-6150 |
| DOI: | 10.1007/s10973-020-09852-z |
| Popis: | Complex perovskites BaCa(1 + y)/3Nb(2 − y)/3O3 − δ (y = 0, 0.18 and 0.5) with 1:1-ordered structure ( $$ Fm\bar{3}m $$ space group) were synthesized by standard ceramic technique. The enthalpy increments for these oxides were measured in the temperature range of (295–1273) K by drop calorimetry, and experimental points were fitted with an integral of a single Einstein term. The hydration enthalpies for BaCa(1.18)/3Nb(1.82)/3O2.91 (BCN18), directly measured by calorimetry, were found to be equal to (− 86.7 ± 4.2) kJ (mol H2O)−1 and (− 88.8 ± 4.0) kJ (mol H2O)−1 at (673.8 ± 0.8) K and (872.8 ± 1.1) K, respectively. The calorimetrically determined enthalpies of hydration were found to be in agreement with those calculated using water vapor pressure–temperature–composition data. The increase in the off-stoichiometry index y in BaCa(1 + y)/3Nb(2 − y)/3O3 − δ leads to more exothermic hydration heats. The enthalpies of formation from elements, determined by drop solution calorimetry for dehydrated BaCa(1 + y)/3Nb(2 − y)/3O3 − δ with y = 0, 0.18 and 0.5, become less exothermic with increasing calcium content, and are equal to (− 1577.5 ± 14.5) kJ mol−1, (− 1533.6 ± 14.8) kJ mol−1 and (− 1492.2 ± 14.6) kJ mol−1, respectively. The thermodynamic data obtained allow calculating the enthalpies of formation and enthalpy increments for BaCa(1 + y)/3Nb(2 − y)/3O3 − δ with arbitrary water content. |
| Databáze: | OpenAIRE |
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