This work evaluates microwave-assisted calcination as a rapid, energy-efficient alternative to conventional resistive heating for complex oxide synthesis. Ce0.9Gd0.1O1.95 (GDC10) and La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF6428) were investigated using solid-state and co-precipitated precursors to assess the influence of precursor chemistry on microwave coupling, reaction kinetics, and powder characteristics. Experiments were conducted in a single-mode magnetic-field-extended reactor using a silicon carbide/alumina susceptor–insulation package to ensure uniform and reproducible heating. Microwave processing reduced calcination time to ~1 h, compared to >21 h in a conventional furnace, while yielding powders with 28% higher surface area. High-temperature dielectric measurements of LSCF (450–1000 oC) revealed strong temperature-dependent increases in dielectric constant and loss factor, governing self-heating behavior and distinct microwave-driven reaction pathways. Phase evolution and surface area were characterized by TGA, XRD, and BET. These results clarify microwave–material coupling mechanisms and demonstrate synergistic effects between precursor chemistry and microwave heating in complex oxide synthesis.