The microstructure, lattice parameters, electrical conductivity, thermal expansion, and mechanical properties of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δ (x = 0.03, 0.06, 0.09, 0.12) were systematically investigated in this work. Nickel doping of (La0.8Ca0.2)(Cr0.9Co0.1)O3–δ is an effective way of increasing the thermal expansion coefficient (TEC) and stabilizing the high-temperature phase transformation from rhombohedral to tetragonal. As the nickel-doped content increases, the TEC increases parabolically by TEC (x) (ppm/°C) = 10.575 + 63.3x−240x2 (x = 0.03−0.12). The electrical conductivity of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δ specimens increases systematically with increasing nickel substitution in the range of 0.03 ≤ x ≤ 0.09 and reaches a maximum for the composition of (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δ (σ850 °C ∼60.36 S/cm). There is a slight increase in the fracture toughness with increasing nickel doping content, and the fracture toughness is strongly affected by the grain size. It seems that there is an increase in the fracture toughness with decreasing grain size. However, the microhardness does not significantly depend on the grain size in this study. The (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δ specimen shows high electrical conductivity, a moderate thermal expansion coefficient, and nearly linear thermal expansion behavior from room temperature to 800 °C. It will be suitable for interconnect materials for intermediate temperature solid oxide fuel cells (IT-SOFCs).
