Two-step sintering technique for enhancing mechanical and oxygen permeation properties of dual-phase oxygen transport membranes

•Both sintering conditions (CS and TSS) exhibited similar relative densities and negligible effect on the structural and elastic properties.•With the use of TSS, about 31 % (142 → 187 MPa) and 7% (8.71 → 9.31 GPa) increase in flexural strength and hardness values, respectively, was observed.•TSS membrane showed remarkably 1.5‒2 times higher oxygen permeation flux than membrane sintered by CS method.•CS membrane showed 2‒10 times lower conductivities than TSS membrane between 850 to 650 °C.•TSS is an effective approach in controlling the microstructures and thus enhancing the mechanical and oxygen permeation properties.