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In this study, bulk and porous SiOC materials were synthesized via a polymer-derived ceramic (PDC) method from a base polysiloxane (PSO) precursor and an iron (Fe) catalyst under an inert pyrolytic atmosphere. Fe catalyzes not only the formation and nucleation of β-SiC at lower temperatures but also promotes phase separation of the amorphous SiO x C y phase, compared to PDCs without the Fe catalyst. Samples with Fe pyrolyzed at 1100 °C have an appreciable β-SiC content compared to a negligible/unobservable β-SiC content in the corresponding Fe-less samples. Selective etching of the SiO 2 phase shows that Fe also induces segregation of the amorphous SiO x C y phase, yielding larger specific surface areas and gas sorption capability below 1300 °C. At 1500 °C, the pore structure changes to form interconnected networks due to the highly phase separated SiO 2 and β-SiC microstructure. A Gibbs free energy minimization method was used to determine the relative phase content of the pyrolyzed samples, with the effect of Fe quantified with simplified vapor–liquid–solid (VLS), solid–liquid–solid (SLS), and classical nucleation theories.