The SFMNR sample sintered at 1000 °C for 4 h exhibits a cubic structure with a space group of Pm-3m (Figure ). In-situ XRD characterizations up to 800°C in a 10%H2/N2 atmosphere indicate that the primary phase remains stable, with the lattice parameter increasing from 3.91 Å at room temperature to 3.98 Å at 800°C. The increased lattice parameters at higher temperatures are attributed to thermal expansion, cation reduction, and oxygen vacancy formation in the lattice (Figures and). Temperature programmed reduction (TPR) in a 5% H2/Ar atmosphere (Figure ) reveals that the desorption temperature of oxygen from the Sr2Fe1.5Mo0.5O6-δ (SFM) sample is 450°C, while the SFMNR sample exhibits the desorption temperatures of 340°C and 770°C. This reduction of 110°C in the SFMNR sample, attributed to the substitution of the B-site cation with 5 at% Ni and Ru in the SFM perovskite, suggests weakened chemical bonding within the BO6 octahedra. The high-temperature peak at 770°C indicates further reduction associated with the formation of Fe-Ni-Ru alloys. In situ XRD at 800 o C under various atmospheres, in fact, shows a slight intensity increase at 43.4°, indicative of Fe-Ni-Ru alloy nucleation under a reducing environment over a duration of 1 h (Figures ).