A new thermodynamic-based design was proposed to improve the stability of La2NiO4 (+) (delta) (LNO) in the presence of lanthanum doped-ceria. Phase analysis of La2NiO4 (+) (delta):LaxCe1 - xO2 (-) (delta) (LNO:LDC) composites (sintered at 1300 degrees C) was studied via X-ray diffraction (XRD) as a function of dopant concentration in the ceria phase (0.2 < x < 0.48) and volume fractions of LNO in the composite. Previously studied sub-solidus phase equilibria between NiO, La2O3, and CeO2 at 1200 degrees C was revisited and studied at 1300 degrees C and 800 degrees C. A thermodynamics-based design for LNO:LDC composites was suggested to improve the phase stability of the LNO component. Elemental analysis via wavelength dispersive X-ray spectroscopy (WDS) confirmed the chemical composition of the stable phases in the composites. The coefficient of thermal expansion (CTE) of LNO:LDC composites as a function of LNO volume fraction further supported the stability of LNO and LDC (for x = 0.4). Additionally, electrical conductivities of La2NiO4 (+) (delta):La0.4Ce0.6O2 (-) (delta) composites were evaluated as a function of LNO volume fraction between 600 and 800 degrees C in air. The electrical conductivity behavior was then analyzed via the resistive network approach, and electronic conductivity of LDC and ionic conductivity of LNO were modeled.