Construction of structural phase diagram of Nd2Ni1-xCuxO4+δ and effect of crystal structure and phase transition on electrical conduction behavior

The structural phase diagram of Nd2NiO4-Nd2CuO4 system, which has potential as new cathode material for solid oxide fuel cells, is established using HT-XRD and SEM-EDX. The Nd2Ni1-xCuxO4+delta showed single phase of orthorhombic and tetragonal K2NiF4-type crystal structure for 0.0 <= x <= 0.1 and 0.2 <= x <= 0.3, respectively. For the specimens with x = 0.0 and 0.1, phase transition from orthorhombic to tetragonal K2NiF4 phase was detected at 570 degrees C and 530 degrees C, respectively. The specimens with 0.4 <= x <= 0.9 were mixture of tetragonal K2NiF4 type structure and Nd2CuO4-type structure owing to the miscibility gap, which remained between 30 and 1000 degrees C in air. The electrical conductivity increased by increasing the Cu content from 0.0 to 0.3, which may be due to the decrease in the electrical resistivity at the grain boundary owing to the increased particle size; however, it decreased by further substitution to 0.4, which was attributed to the generation of the Nd2CuO4 phase by the miscibility gap.