Thermodynamics of BaCa(1 + y)/3Nb(2 − y)/3O3 − δ·xH2O proton-conducting perovskites

• Published in: Journal of thermal analysis and calorimetry Vol. 142; no. 5; pp. 1989 - 2001
• Main Authors: Sereda, V. V., Sednev-Lugovets, A. L., Malyshkin, D. A., Ivanov, I. L., Tsvetkov, D. S., Zuev, A. Yu
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2020; Springer Nature B.V
• Subjects: Analytical Chemistry; Chemistry; Chemistry and Materials Science; Dehydration; Enthalpy; Heat measurement; Hydration; Inorganic Chemistry; Mathematical analysis; Measurement Science and Instrumentation; Moisture content; Perovskites; Physical Chemistry; Polymer Sciences; Stoichiometry; Vapor pressure; Water vapor; Hydration enthalpy; Formation enthalpy; Proton-conducting perovskites; Enthalpy increments
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-020-09852-z

Complex perovskites BaCa (1   +   y)/3 Nb (2   −   y)/3 O 3   −   δ ( y  = 0, 0.18 and 0.5) with 1:1-ordered structure ( F m 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)/3 Nb (1.82)/3 O 2.91 (BCN18), directly measured by calorimetry, were found to be equal to (− 86.7 ± 4.2) kJ (mol H 2 O) −1 and (− 88.8 ± 4.0) kJ (mol H 2 O) −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)/3 Nb (2   −   y)/3 O 3   −   δ leads to more exothermic hydration heats. The enthalpies of formation from elements, determined by drop solution calorimetry for dehydrated BaCa (1   +   y)/3 Nb (2   −   y)/3 O 3   −   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)/3 Nb (2   −   y)/3 O 3   −   δ with arbitrary water content.