As one of the most essential electrochemical devices for a sustainable zero pollution future, ceramic membrane reactor has been developed for high purity O2 production and partial oxidation of CH4, as well as water splitting. The performance of the reactor is governed by the oxygen transport membrane made of mixed ionic and electronic conducting oxide. The classic single-phase membrane materials, e.g. barium/lanthanum strontium cobalt ferrite perovskite-type oxides, suffer from irreversible material deteriorations in application-relevant conditions despite the high oxygen permeation. By contrast, dual phase membrane materials combined from an ionic conductive oxide, e.g. Gd doped CeO2, and an electronic conductive oxide, e.g. iron cobalt/nickel spinel, possess high tolerance in CO2- and SO2-containing gas mixtures, and thus show good chemical stability for long term operation. However, their transport properties and oxygen permeation are commonly not competitive to those of single-phase perovskite compounds. The aim of the current work is to optimize the performance of dual phase membrane materials via tailoring the sintering profile. The 85 wt% Ce0.8Gd0.2O2-d-15 wt% FeCo2O4 membrane material is studied as an example, and prepared via solid state reactive sintering from commercially available Ce0.8Gd0.2O2-d, Fe2O3, and Co3O4 powders. A highly densified membrane is sintered using a comparably low temperature of 1050 °C, and exhibits the highest oxygen performance. The mechanism for the enhanced performance is explored through nano- and microscale investigations and revealed to be strongly associated to the successful tuned microstructure and phase interaction, as well as elemental interdiffusion.