Study The Electrical Properties Of Perovskite Cobalt Oxide Preparation And Electroluminescence

CER materials in recent years has become a large area of concern to thescientists a hot topic. The perovskite cobaltates have attracted significant scientificattention due to their Colossal Magnetoresistnace effect （CMR） and charge orderphenomena, their Colossal Magnetoresistnace effect have very broad prospect ofapplication in magnetic storage, magnetic sensor pieces, spin valve and spintransistor. In cobaltate system, freedoms of spin, charge, rail and crystal lattice havestrong relevance, their interaction and mutual competition caused rich physicalphenomenon, which led that the transport properties of cobaltate very sensitive tothe magnetic field and the electric field. In the last few years, a new physicalphenomenon known as the resistance switching effect, which is induced by anelectric current or electric field, has become an interesting topic of study forgeneration non-volatile memory.In this work, conventional solid state reaction method was used to preparepolycrystalline samples of perovskite cobaltites Nd_1xSr_xCoO₃（NSCO） ceramics. Thecomposition, morphology, R-T, I-V, magnetoresistance effect and electroresistanceeffect were systematically studied. In order to promote of the giant electroresistanceeffect with perovskite cobalt oxide material, sol-gel method was used to preparepolycrystalline samples of perovskite cobaltites Nd_1xSr_xCoO₃films andLa1-xNaxCoO3（LNCO） films. The main works in this dissertation are as follows:1. Conventional solid state reaction method was used to prepare polycrystallinesamples of perovskite cobaltites Nd_1xSr_xCoO₃ceramics. The samples have the sameorthorhombic perovskite structure with Pbnm space group at room temperature. Theresistivity of the samples decrease dramatically with the currents increase especiallyin the low temperatures. When the Sr contents increase, the resistivity of thesamples reduces gradually in the whole temperature measurement range due to thehole doping. The maximum ER ratios was-99.51%in the low temperature. It’s thatthe ER ratios at room temperature was-81.31%. We propose FM/NM interfaceregion may be converted to FM metallic by injected current, result in the reduction of resistivity and CER effect in the polycrystalline perovskite cobaltites NSCO.2. Sol-gel method was used to prepare polycrystalline samples of perovskitecobaltites Nd_1xSr_xCoO₃（LNCO）. The resistivity of the samples decrease dramaticallywith the currents increase especially in the low temperatures. The I-V curve ofnonlinear hysteresis phenomenon is observed in x=0.18. Positive and negativeelectric resistance ratio are calculated and one of the biggest ratio is-99.6%. Inx=0.26, it appears giant magnetoresistance and reaches489%.3. Sol-gel method was used to prepare polycrystalline samples of perovskitecobaltites La1-xNaxCoO3（LNCO） films. No obvious peak shift with Na content isdetected from the XRD results; that means the structure of Na-doped samples is notobviously changed. The resistivity of all the four samples decrease dramatically withthe currents increase especially in the low temperatures. When the Na contentsincrease, the resistivity of the samples reduces gradually in the whole temperaturemeasurement range due to the hole doping. The maximum ER ratios was-99.0%inthe low temperature. It’s worth noting that the ER ratios at room temperature of thesamples was-98.4%. Typical non-linear I-V characteristics are observed.