Electronic Conduction Mechanisms in BaTiO 3 –Ni Composites with Ultrafine Microstructure Obtained by Spark Plasma Sintering

Spark plasma sintering (SPS) was used to densify BaTiO 3 –Ni composite powders to relative densities above 92.8%. With the increasing Ni content, a decrease in relative density is observed, suggesting that Ni hampers the consolidation process. The microstructures of the BaTiO 3 –Ni composites were of duplex character. The crystallite size of the BaTiO 3 ‐grains was around 100 nm in average. The ceramic matrix phase of BaTiO 3 surrounded Ni inclusions of approximately 1 μm in diameter that were completely incorporated without the formation of any elongated metallic filaments. The ac conductivity of these BaTiO 3 –Ni composites increased with increasing Ni content and with temperature. The dominant conduction mechanisms in SPSed BaTiO 3 –Ni composites showed quite a complicated behavior. A gradual change from band conduction of trapped electrons in oxygen vacancies to a hopping‐type motion of small polarons between Ti 4+ and Ti 3+ is suggested to occur, when the Ni content increases. The influence of oxygen vacancies and other lattice defects on the electrical properties of BaTiO 3 –Ni composites is discussed.