(Ba,Ca)TiO sub(3) PTCR Ceramics with LaNiO sub(3) Thin-Film Electrodes: Preparation and Characterization of the Interface

Conductive LaNiO sub(3) thin film electrodes were deposited by chemical solution deposition (CSD) from nitrate solutions onto polycrystalline Al sub(2)O sub(3) and (Ba,Ca)TiO sub(3) PTCR ceramic substrates. The electrical properties of the LaNiO sub(3) thin film on Al sub(2)O sub(3) and of the interface consisting of LaNiO sub(3) and the semiconductive oxide ceramic were investigated. The deposited LaNiO sub(3) films were about 250 nm thick and consisted of nanosized particles. The resistivity of the LaNiO sub(3) film was about 3 10 super(-3) Omega cm at 20 degree C. The PTCR ceramic consisted of mu m sized particles and exhibited an electronic resistivity of about 10 Omega cm at 20 degree C and a steep increase of the resistivity of a few orders of magnitude above the Curie point at about 120 degree C. The electrical properties of the LaNiO sub(3)/PTCR interface were dominated by the properties of a barrier layer between the PTCR ceramic and the LaNiO sub(3) electrode. The potential dependence of the impedance indicated that the barrier layer consisted of a depletion layer within the PTCR ceramic, when the flat band potential of LaNiO sub(3) on the PTCR ceramic at about -250 mV was exceeded. Additionally the formation of an insulating layer at the LaNiO sub(3) electrode has to be taken into account.