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

• Published in: Applied sciences Vol. 11; no. 13; p. 5939
• Main Authors: Natoli, Alejandro, Frade, Jorge R., Bamburov, Aleksandr, Żurawska, Agnieszka, Yaremchenko, Aleksey
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2021
• Subjects: Air temperature; Alternative energy sources; Cations; Ceramics; Conduction; Conductors; Cooling; Electrical conductivity; Electrical resistivity; Electrodes; Electrolytes; Electrolytic cells; Energy conversion; Energy storage; Fluorite; Fuel cells; High temperature; ionic conductivity; Oxidation; Partial stabilization; Partially stabilized zirconia; Point defects; Porosity; Praseodymium; Praseodymium oxide; Radiation; Renewable resources; solid electrolyte; Solid electrolytes; Solid solutions; Thermal expansion; Transport properties; yttria-stabilized zirconia; Yttrium oxide; Zirconia; Zirconium dioxide; Portugal
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app11135939

Ceramics samples with the nominal composition [(ZrO2)0.95(Y2O3)0.05]1-x[PrOy]x and praseodymia contents of x = 0.05–0.15 were prepared by the direct firing of compacted 5YSZ + PrOy 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 PrOy 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 p-type electronic contribution increasing with Pr content but not exceeding 2% for x = 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.