| The impacts of defect chemistry on a perovskite oxide are significant. A mass of oxygen vacancies defects exist in the oxide if it is annealed in nonstoichiometric oxygen atmospheres. Epitaxial LaNiO3, La0.5Sr0.5CoO3 and Pb(Zr0.4Ti0.6)O3 have been prepared, and the impact of the cooling oxygen pressure on the structure and physical properties of the films is investigated especially.1. La0.5Sr0.5CoO3(70 nm)/Pb(Zr0.4Ti0.6)O3(70nm)/La0.5Sr0.5CoO3(70nm)(LSCO/PZT/LSCO) capacitor is fabricated on SrTiO3(001) substrate using RF magnetron sputtering and pulsed laser deposition (PLD). It is found that the coercive voltage, remnant polarization, leakage current density and the maximum dielectric constant of LSCO/PZT/LSCO capacitor, measured at the voltage of 5 V, are 0.49 V, 41.7μC/cm2, 1.97×10-5 A/cm2, 1073, respectively. Leakage current density of the LSCO/PZT/LSCO capacitor is further investigated, which meets ohmic behavior at low voltage(<0.6 V) and agrees well with the space-charge-limited current (SCLC) theory at higher voltage(>0.6 V).2. La0.5Sr0.5CoO3 (LSCO) and LaNiO3 (LNO) thin films have been prepared by rf magnetron sputtering method in different annealing oxygen pressures and the impact of cooling oxygen pressure on the structural and transport properties is investigated. X-ray diffraction shows LSCO (002) peaks left shifted with reducing cooling oxygen pressure. The lattice constants and resistivities of LSCO films increase with reducing cooling oxygen pressure. AFM images indicate that cooling oxygen pressure greatly impacts the morphologies of LSCO films. Grain size of LSCO film decreases with the decrease of cooling oxygen pressure, and very smooth LSCO surface with extreme ultrafine and uniform grains is obtained for the LSCO/STO sample cooled at 1×10-4 Pa. In comparison to LSCO films, the properties of LNO films change smaller with the reduction of cooling oxygen pressure. LSCO films are more sensitive to oxygen atmosphere.3. La0.5Sr0.5CoO3 (LSCO) bottom electrodes grown on SrTiO3 (STO) substrates is annealed in oxygen pressures ranging from 8×104 to 1×10-4 Pa, and the impact of the LSCO bottom electrodes on the structure and physical properties of epitaxial La0.5Sr0.5CoO3/PbZr0.4Ti0.6O3/La0.5Sr0.5CoO3 (LSCO/PZT/LSCO) capacitors is investigated. It is found that ferroelectric properties of LSCO/PZT/LSCO capacitors strongly depend on the annealing oxygen pressures of the LSCO bottom electrodes. The higher annealing oxygen pressure of the LSCO bottom electrodes, the larger the switchable polarization of the LSCO/PZT/LSCO capacitor. Serious fatigue phenomena is observed when LSCO bottom electrodes are cooled in reducing oxygen pressure, ~ 60% maximum polarization degradation occurs for the capacitor with LSCO bottom electrodes cooled in 1×10-4 Pa oxygen, indicating oxygen vacancy of bottom electrode can result in fatigue of LSCO/PZT/LSCO capacitor. |
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