Plasma dynamic synthesis of composite ZnO-Bi₂O₃ material with a core-shell structure for varistor ceramics

Zinc oxide has been studied for many years and found many applications in different areas, including the power engineering, where the ZnO-based ceramics could be used as a varistor. However, there is a necessity to add different oxides to ZnO to make a uniform ceramics structure with well enough nonlinear characteristics. In this regard, the uniform distribution of additives in the structure of a composite based on ZnO becomes an urgent task to prepare the high-quality ceramics. This work shows the possibility to obtain the composite powdered material with the uniformly distributed Bi₂O₃ addition in the ZnO crystallites by a plasma dynamic method. The features of this method and flowing reactions allow forming the ZnO-Bi₂O₃ particles with the core-shell structure. The spark plasma sintering of the ZnO-Bi₂O₃ composite material with such particles structure provides the production of varistor ceramics characterized by a fine-grained ZnO structure (average grain size is about 1 µm) with uniformly filled intergranular spaces by Bi₂O₃. The comparison of voltage-current characteristics with the ceramics made of ball-milled commercial powders showed the prospects of using as-prepared ZnO-Bi₂O₃ composite with core-shell structure.