Electronic Conduction Mechanisms in BaTiO3-Ni Composites with Ultrafine Microstructure Obtained by Spark Plasma Sintering

Abstract

Spark plasma sintering (SPS) was used to densify BaTiO3–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 BaTiO3–Ni composites were of duplex character. The crystallite size of the BaTiO3-grains was around 100 nm in average. The ceramic matrix phase of BaTiO3 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 BaTiO3–Ni composites increased with increasing Ni content and with temperature. The dominant conduction mechanisms in SPSed BaTiO3–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 Ti4+ and Ti3+ is suggested to occur, when the Ni content increases. The influence of oxygen vacancies and other lattice defects on the electrical properties of BaTiO3–Ni composites is discussed.