Nonohmic behavior of SnO2-MnO polycrystalline ceramics.: I.: Correlations between microstructural morphology and nonohmic features

This report discusses important microstructural features of SnO2.MnO-based polycrystalline ceramics. The influence of the sintering time and the concentration of donor Nb2O5 on the microstructure of these ceramics are investigated, and the correlation between the microstructural features and nonohmic behavior are also discussed. High resolution analytical electron microscopy was used for a detailed characterization of the microstructure and grain boundary chemistry of the compositions, revealing that SnO2-MnO dense ceramics consist of two phases, SnO2 grains and Mn2SnO4, precipitated mainly at triple grain points. In addition, two types of SnO2-SnO2 grain boundary were identified: type I, Mn-rich and thin, and type II, Mn-poor and thick. Changes in Mn concentrations at the grain boundaries are ascribed to both grain misorientation and Mn diffusivity along the grain boundary. The identification of two kinds of junctions in SnO2-MnO has significant implications in the material's nonohmic behavior, as will be discussed in detail here and in Part II, and is important in understanding the sintering mechanism and microstructural formation of SnO2 ceramics. (C) 2004 American Institute of Physics.