Synthesis and investigation of solid solutions based on praseodymium oxide in a Pr6O11– MoO3system

Abstract

To enhance mixed ionic-electronic conductivity in praseodymium oxide for SOFC applications, novel Mo-substituted Pr6O11 solid solutions (0–16.67 mol.% MoO3) were synthesized via solid-state reaction in air. Phase purity was confirmed by X-ray diffraction analysis, while homogeneity and uniformity were verified through EDX mapping. The system exhibits exceptional MoO3 solubility despite significant cation size and charge mismatch (r(Mo6+) = 0.59 Å, c.n. = 6 vs. r(Pr3+/Pr4+) = 1.13/0.96 Å, c.n. = 8). The crystal structure was refined using high-resolution time-of-flight neutron diffraction data, confirming a disordered fluorite structure (space group Fm3m) with anomalous oxygen displacement (Biso > 3 Å2). Electrical properties, investigated via impedance spectroscopy, revealed a composition-dependent transition in conductivity. Below 11 mol.% MoO3, bulk conductivity decreased due to Pr4+ reduction and suppressed electronic contribution. Remarkably, at 11.11 mol.% MoO3, enhanced conduction yielded a maximum conductivity 3.2 × 10−3 S/cm at 700 °C, comparable to undoped Pr6O11. Impedance spectra showed emergent low-frequency arcs above 600 °C in Mo-rich compositions, possibly signifying activated oxygen-ion transport. The incorporation of molybdenum oxide into Pr6O11 in an amount greater than 4 % increases the stability of the material during storage by preventing adsorption of atmospheric components. This study establishes Mo-doped Pr6O11 as a promising electrode material for intermediate-temperature SOFCs.