Conductivity, structure, and thermodynamics of Y 2 Ti 2 O 7 –Y 3 NbO 7 solid solutions

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-08, Vol.49 (31), p.10839-10850
• Main Authors: Winiarz, Piotr, Mielewczyk-Gryń, Aleksandra, Lilova, Kristina, Wachowski, Sebastian, Subramani, Tamilarasan, Abramchuk, Mykola, Dzik, Ewa, Navrotsky, Alexandra, Gazda, Maria
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/D0DT02156C

The defect fluorite yttrium niobate Y 3 NbO 7 and pyrochlore yttrium titanate Y 2 Ti 2 O 7 solid solutions have been synthesized via a solid state synthesis route. The resulting stoichiometry of the oxides is Y 2+x Ti 2−2x Nb x O 7 , 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 calculated 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 Y 3 NbO 7 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.