(Ba, Ca)TiO3 PTCR ceramics with LaNiO3 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^sup -3^Ωcm at 20°C. The PTCR ceramic consisted of μm sized particles and exhibited an electronic resistivity of about 10 Ωcm at 20°C and a steep increase of the resistivity of a few orders of magnitude above the Curie point at about 120°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.[PUBLICATION ABSTRACT]