Jose J. Saavedra-Arias

High energy density metal-insulator-metal capacitors with Ba[(Ni1∕2,W1∕2)0.1Ti0.9]O3 thin films

Metal-insulator-metal capacitors with high-k Ba[(Ni1∕2,W1∕2)0.1Ti0.9]O3 thin film dielectrics were fabricated by chemical solution deposition technique. High dielectric constant (85), low dielectric loss (0.007), and high breakdown field (∼3.0MV∕cm) at room temperature were achieved. The temperature and frequency dependences of capacitance and loss tangent were small around room temperature (300±25K). At room temperature, high capacitance density (3.1fF∕μm2) along with high energy density (34J∕cm3) and low leakage current (7.7×10−6A∕cm2 at 20V) were obtained, indicating high potential for this material in the integrated circuits and power electronic applications.

Structural and Electrochemical Characterization of Pure LiFePO 4 and Nanocomposite C- LiFePO 4 Cathodes for Lithium Ion Rechargeable Batteries

Pure lithium iron phosphate () and carbon-coated (C-) cathode materials were synthesized for Li-ion batteries. Structural and electrochemical properties of these materials were compared. X-ray diffraction revealed orthorhombic olivine structure. Micro-Raman scattering analysis indicates amorphous carbon, and TEM micrographs show carbon coating on particles. Ex situ Raman spectrum of C- at various stages of charging and discharging showed reversibility upon electrochemical cycling. The cyclic voltammograms of and C- showed only a pair of peaks corresponding to the anodic and cathodic reactions. The first discharge capacities were 63, 43, and 13 mAh/g for C/5, C/3, and C/2, respectively for where as in case of C- that were 163, 144, 118, and 70 mAh/g for C/5, C/3, C/2, and 1C, respectively. The capacity retention of pure was 69% after 25 cycles where as that of C- was around 97% after 50 cycles. These results indicate that the capacity and the rate capability improved significantly upon carbon coating.

Electrochemical Hydrogen Oxidation on Pt(100): a Combined Direct Molecular Dynamics/Density Functional Theory Study

We have studied the hydrogen oxidation reaction on various catalytic sites at the water/Pt(100) interface with first-principles direct molecular dynamics and minimum energy pathway calculations. The calculations indicate that the mechanism for electro-oxidation of H2 on terrace sites of the Pt(100) surface depends on the concentration of inactive adsorbed hydrogen on the electrode surface. Near the reversible potential, the electro-oxidation follows the Tafel-Volmer homolytic cleavage of H2 at low coverage of adsorbed hydrogen. If the surface is covered with ca. 1 monolayer of hydrogen, however, the oxidation proceeds by the Heyrovsky-Volmer mechanism. We found good agreement between measured and predicted Tafel plots, indicating that hydrogen oxidation/reduction reaction on Pt(100) takes place via the Heyrovsky-Volmer mechanism under ca. 1 monolayer coverage of inactive adsorbed hydrogen.

Structural and Electrochemical Characterization of Pure and Nanocomposite C- Cathodes for Lithium Ion Rechargeable Batteries

Pure lithium iron phosphate () and carbon-coated (C-) cathode materials were synthesized for Li-ion batteries. Structural and electrochemical properties of these materials were compared. X-ray diffraction revealed orthorhombic olivine structure. Micro-Raman scattering analysis indicates amorphous carbon, and TEM micrographs show carbon coating on particles. Ex situ Raman spectrum of C- at various stages of charging and discharging showed reversibility upon electrochemical cycling. The cyclic voltammograms of and C- showed only a pair of peaks corresponding to the anodic and cathodic reactions. The first discharge capacities were 63, 43, and 13 mAh/g for C/5, C/3, and C/2, respectively for where as in case of C- that were 163, 144, 118, and 70 mAh/g for C/5, C/3, C/2, and 1C, respectively. The capacity retention of pure was 69% after 25 cycles where as that of C- was around 97% after 50 cycles. These results indicate that the capacity and the rate capability improved significantly upon carbon coating.

Structural and Electrochemical Characterization of PureLiFePO4and Nanocomposite C-LiFePO4Cathodes for Lithium Ion Rechargeable Batteries

Pure lithium iron phosphate () and carbon-coated (C-) cathode materials were synthesized for Li-ion batteries. Structural and electrochemical properties of these materials were compared. X-ray diffraction revealed orthorhombic olivine structure. Micro-Raman scattering analysis indicates amorphous carbon, and TEM micrographs show carbon coating on particles. Ex situ Raman spectrum of C- at various stages of charging and discharging showed reversibility upon electrochemical cycling. The cyclic voltammograms of and C- showed only a pair of peaks corresponding to the anodic and cathodic reactions. The first discharge capacities were 63, 43, and 13 mAh/g for C/5, C/3, and C/2, respectively for where as in case of C- that were 163, 144, 118, and 70 mAh/g for C/5, C/3, C/2, and 1C, respectively. The capacity retention of pure was 69% after 25 cycles where as that of C- was around 97% after 50 cycles. These results indicate that the capacity and the rate capability improved significantly upon carbon coating.

Effect of Sr substitution on tunability and dielectric properties in Pb(Zr0.50Ti0.50)O3 thin films fabricated by chemical solution deposition

(Pb1¿xSrx)(Zr0.5Ti0.5)O3 ( x= 0 to 0.65) thin films were grown on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. Films were crystallized in the single phase perovskite structure in the temperature range ( 550¿700°C). Dielectric constant and loss tangent at room temperature reduced as the percentage of Sr substitution increased at the A-site of this perovskite structure. The phase transition temperature (Tc) lowered with Sr-substitution and Tc below the room temperature was obtained for composition with Sr ¿ 40%. The room temperature tunability reduced with Sr substitution, however, the k-factor slightly improved.