Microstructure evolution and conductivity of Bi2CuO4–Bi2O3 composites nearby the eutectic point

In the present work, the detailed investigation of microstructure evolution of Bi2CuO4–Bi2O3 composites nearby the eutectic point (770 °C) was carried out by scanning electron microscopy. For this purpose, the microstructure of Bi2CuO4+20 wt.% of Bi2O3 samples quenched at 750, 760, 765, 770, 775 and 780 °C was investigated. It has been found that initially randomly distributed Bi2O3 became localized at three-grain junctions and Bi2CuO4 grain boundaries after quenching from temperatures above the eutectic point. Such evolution in location of Bi2O3 is most likely caused by grain boundary wetting and grain boundary liquid channel structure (GBLCS) formation. Conductivity measurements of Bi2CuO4–Bi2O3 composites were performed by four-point DC technique and two-point AC impedance spectroscopy in the temperature range 660–790 °C in air. It was shown that conductivity vs. temperature dependences of Bi2CuO4+10, 20 wt.% of Bi2O3 composites exhibit jump near 770 °C. The observed conductivity jump once more supports the processes of grain boundary wetting and grain boundary liquid channel structure formation.