Origin of micro-scale local hotspots during the microwave processing of the YBCO conductive ceramics

In this letter, in situ investigation on the microstructure evolution of YBa2Cu3O7-x (YBCO) ceramics with a high electrical conductivity on a microscopic scale during microwave heating was carried out by the synchrotron radiation computed tomography technique. The experimental results indicate that the local melting exist inside the particle composed of smaller particles, leading to the heterogeneous heating or thermal runaway, which has not been reported elsewhere. Subsequently, considering the conductivity and morphology of YBCO particles, the novel phenomena has been interpreted by the calculated results from a constructed model, and it reveals that the non-uniform distribution of the focused electric field stems from the high conductivity and aggregated-particles of YBCO. Moreover, the high conductivity in combination with more and smaller aggregated-particles will intensify the non-uniformity of the focused electric field and heterogeneous heating for different microstructures.