Coalescence growth mechanism of inserted tin dioxide belts in polycrystalline SnO2-based ceramics

SnO2-based varistors have been considered promising technological devices. However their practical application is usually stated as limited to high voltage circuits based on the high breakdown electric field exhibited by these ceramics. Recently, authors have shown that the insertion of one-dimensional (1D) SnO2 belts allows overcoming this limitation. In this work, we present a detailed study of the growth mechanism of the belts inside varistors using electron microscopy techniques. We were able to show that mass transport has an intrinsic dependence on the sintering time and requires similar crystalline structure between the belts and the matrix. Dual beam and high-resolution transmission electron microscopy techniques permitted determining that 3D growth of belts occurs by coalescence. [Display omitted] •Grain growth in SnO2-based varistors was studied.•The growth of 1D SnO2 belts in the SnO2-CoO-Cr2O3-Nb2O5 system occurs by coalescence process.•Cross-Section and Tomography images showed tridimensional and pore free “giant grains”.•TEM was used to prove the alignment of the grains towards the SnO2 belt.•The coalescence growth just occurs with 1D structure and grains having the same crystal structure.