Microstructural analysis of Nd1.85Ce0.15CuO4−y superconductor sintered under high pressure and ambient pressure

The microstructure of Nd_1.85Ce_0.15CuO_4−y superconductor sintered under high pressure and ambient pressure has been characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HREM). It has been observed that the conventional sample is porous, while the high-pressure sample is almost pore-free. It is confirmed that the thermal treatment under high pressure recovers fairly well connections between grains which were partly crushed during the compression process; hence the weak links at grain boundary are improved. Furthermore, a high density of defects induced by pressure is observed in the high-pressure sample. In contrast, the conventional sample is nearly perfect. For comparison, the microstructure of a sample pressed at high pressure at room temperature is also examined. The influence of pressure on the microstructure and the superconductivity is discussed.