Impact of Praseodymia Additions and Firing Conditions on Structural and Electrical Transport Properties of 5 mol.% Yttria Partially Stabilized Zirconia (5YSZ)

• Main Authors: Alejandro Natoli, Jorge R. Frade, Aleksandr Bamburov, Agnieszka Żurawska, Aleksey Yaremchenko
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Applied Sciences
• Subjects: solid electrolyte; yttria-stabilized zirconia; praseodymium oxide; electrical conductivity; ionic conductivity; thermal expansion
• Online Access: https://www.mdpi.com/2076-3417/11/13/5939

Ceramics samples with the nominal composition [(ZrO₂)_0.95(Y₂O₃)_0.05]_1-<i>x</i>[PrO<i>_y</i>]<i>_x</i> and praseodymia contents of <i>x</i> = 0.05–0.15 were prepared by the direct firing of compacted 5YSZ + PrO<i>_y</i> mixtures at 1450–1550 °C for 1–9 h and characterized for prospective applicability in reversible solid oxide cells. XRD and SEM/EDS analysis revealed that the dissolution of praseodymium oxide in 5YSZ occurs via the formation of pyrochlore-type Pr₂Zr₂O₇ intermediate. Increasing PrO<i>_y</i> additions results in a larger fraction of low-conducting pyrochlore phase and larger porosity, which limit the total electrical conductivity to 2.0–4.6 S/m at 900 °C and 0.28–0.68 S/m at 700 °C in air. A longer time and higher temperature of firing promotes the phase and microstructural homogenization of the ceramics but with comparatively low effect on density and conductivity. High-temperature processing leads to the prevailing 3+ oxidation state of praseodymium cations in fluorite and pyrochlore structures. The fraction of Pr⁴⁺ at 600–1000 °C in air is ≤2% and is nearly independent of temperature. 5YSZ ceramics with praseodymia additions remain predominantly oxygen ionic conductors, with <i>p</i>-type electronic contribution increasing with Pr content but not exceeding 2% for <i>x</i> = 0.15 at 700–900 °C. The average thermal expansion coefficients of prepared ceramics are in the range of 10.4–10.7 ppm/K.