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YBCO samples were prepared using different types of precursor powders: quenched, or YBa2Cu3O7−x and Y2BaCuO5 commercial powders, with and without Pt addition. Two stoichiomctrics, corresponding to 0 and 40% molar excess of the Y2BaCuO5 phase, were adopted. The behavior of the Y2BaCuO5 phase through thermal treatments, typical of melt processes, was observed by quenching the samples at various stages. YBa2Cu3O7−x grain growth kinetics was enhanced and liquid phase losses were limited by optimizing the morphology of the Y2BaCuO5 phase in the partially melted state, with the simultaneous presence of round particles ≤1 μm and needle-like particles with very high aspect ratio. The optimized processing conditions were adopted, together with a seeding technique, to grow YBCO samples. At 77 K, a magnetic levitation force of 2.5 kg was measured for a sample with 18 mm diameter, and magnetization critical current densities over 104 A/cm2 were reached at 1 T.

We have studied imprint mechanism of ferroelectric memory based on the oxygen-vacancy screening model. Interface charge density and offset bias for PZT resulted from the imprint were estimated as a function of effective depth for diffusion of oxygen vacancy based on this model. In order to understand microscopic dynamics during the imprint that might affect the interface charge density, molecular dynamics simulation (MD) was carried out. Diffusion length during the real imprint test for PZT was estimated based on the diffusion constant obtained from the MD simulation. By using the diffusion length, interface charge density and, in turn, offset bias was quantitatively estimated. Based on the quantitative analysis, it is found that the oxygen-vacancy screening model with microscopic dynamics obtained from the simulation explains well the imprint mechanism for PZT materials family.

Using first principles calculations, we have investigated the electronic structure of Pb(ZrTiNb)O3 (PZTN), a system with a low leakage current and high reliability in thin films. We proposed that in PZTN, the oxygen vacancy is suppressed due to the addition of a Nb atom at the B site and that this change prevents a bandgap narrowing which would enhance the leakage current. The oxygen vacancy in the perovskite structure reduces the bandgap because it lowers the d orbital energy of the nearest-neighbor transition metal through the Madelung potential; this bandgap narrowing induces the leakage current in conventional Pb(ZrTi)O3 (PZT) systems with the Shottky type Pb-O deficit. In contrast, the PZTN systems, which also have the Pb deficit but lack the oxygen vacancy, can maintain the bandgap, and attain a low leakage current.

Pseudocubic SrRuO3 (100) epitaxial thin films were fabricated on Si (100) with a YBa2Cu3Ox / CeO2 / YSZ (yttria-stabilized-zirconia) triple buffer layer ∼ 14 nm thick by pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) revealed that the first buffer layer of YSZ (100) was epitaxially grown on naturally oxidized Si (100) substrates with the process condition of PB (base pressure) = 1×10-Torr, PO2 (oxygen partial pressure) = 5×10- Torr, and Ts (substrate temperature) = 700 °C. Higher deposition rate of YSZ in the range of 0 ∼ 0.6 nm/min brought about better crystallinity with a smaller value of a full-width at half maximum (FWHM) in the YSZ (200) rocking curve. Subsequent deposition of CeO2, YBa2Cu3Ox, and SrRuO3 resulted in an SrRuO3 (100) epitaxial thin film exhibiting good crystallinity with FWHM = 1.7° in the SrRuO3 (200) rocking curve.