Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution . The presence of such solid solution caused a depression in the superconducting transition temperatures , particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, values of these superconductors were larger than that of a good quality Y123 superconductor in high magnetic fields at 77 K. In this article, on the basis of our study over the last several years, the melt processes for LRE - Ba - Cu - O are described, the microstructural and superconducting properties of the superconductors are reviewed and the flux pinning mechanism is also discussed.

https://iopscience.iop.org/article/10.1088/0953-2048/9/12/001/pdf

Melt-processed light rare earth element - Ba - Cu - O

We review recent progress made in the field of semiconductor spintronics, a branch of semiconductor electronics where both charge and spin degrees of freedom play an important role in realizing unique functionalities. We first describe the new spin-dependent phenomena found in semiconductors including carrier-induced ferromagnetism in III-V compounds, followed by an account of our current understanding of such spin-dependent phenomena. Then we summarize the challenges the semiconductor spintronics has to meet in order for it to be a success as "electronics".

http://ieeexplore.ieee.org/iel5/7729/21698/01005423.pdf

Semiconductor spintronics

Although the vast majority of high-$T_c$ cuprate superconductors are hole-doped, a small family of electron-doped compounds exists. Under investigated until recently, there has been tremendous recent progress in their characterization. A consistent view is being reached on a number of formerly contentious issues, such as their order parameter symmetry, phase diagram, and normal state electronic structure. Many other aspects have been revealed exhibiting both their similarities and differences with the hole-doped compounds. This review summarizes the current experimental status of these materials, with a goal to providing a snapshot of our current understanding of electron-doped cuprates. When possible we put our results in the context of the hole-doped compounds. We attempt to synthesize this information into a consistent view on a number of topics important to both this material class as well as the overall cuprate phenomenology including the phase diagram, the superconducting order parameter symmetry, phase separation, pseudogap effects, the role of competing orders, the spin-density wave mean-field description of the normal state, and electron-phonon coupling.

Progress and perspectives on electron-doped cuprates

Experiments are reported on two techniques for melt‐texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper‐rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser‐heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: ‘‘faceted plane front,’’ ‘‘cellular dendritic’’ or ‘‘equiaxed blocky.’’ The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the ‘‘root’’ of the solidification front dropped, but temperature of the solidification front ‘‘tip’’ did not. A solidification model is ...

Semisolid solidification of high temperature superconducting oxides

Cubic and orthorhombic NaNbO3 were fabricated to study the effects of crystal structure and electronic structure on the photocatalytic activities in detail. The samples were characterized by X-ray diffraction, field emission transmission electron microscopy, high-resolution transmission electron microscopy, UV–visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the two phases of NaNbO3 have been assessed by H2 evolution from aqueous methanol solution and CO2 photoreduction in gas phase. The photocatalytic H2 evolution and CO2 reduction activities over cubic NaNbO3 were nearly twice of those over orthorhombic NaNbO3. The first-principles calculation reveals that the higher activity over cubic NaNbO3 can be attributed to its unique electronic structure, which is beneficial for electron excitation and transfer.

/pdf/the-effects-of-crystal-structure-and-electronic-structure-on-4gg5i6rg72.pdf

The Effects of Crystal Structure and Electronic Structure on Photocatalytic H2 Evolution and CO2 Reduction over Two Phases of Perovskite-Structured NaNbO3

${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ grown by the traveling-solvent floating-zone method shows a large inhomogeneity both in structural and physical properties, such as lattice parameters and transport and magnetic properties. Some parts of this sample exhibit bulk superconductivity. The c-axis lattice constant is longer than that of nonsuperconducting samples grown by the flux method. However, the magnetic susceptibility of the superconducting sample suggests the valence of Pr is $+3$. The superconducting transition temperature exceeds 100 K under a pressure over 8 GPa and still has a potential to increase.

Superconducting PrBa 2 Cu 3 O x

A phase-equilibrium diagram of the ternary system of Y2O3-BaO-CuO was investigated. The temperature vs concentration diagrams are given on four binary systems ranging from YBa2Cu3O7-y to CuO, to BaCuO2·3CuO, to 3BaCuO2·4CuO and to 3BaCuO2·2CuO mixtures. A liquidus line required for the preparation of YBa2Cu3O7-y single crystal from solution was found to be extremely narrow in concentration range.

Phase-Equilibrium Diagram in the Ternary System Y2O3-BaO-CuO

We report the observation of bulk superconductivity in PrBa2Cu3Ox single crystals for the first time. These samples were grown by the travelling-solvent floating-zone (TSFZ) method in oxygen-reduced atmosphere. The as-grown crystal has a longer c-axis lattice constant an than any values previously reported for oxygen-reduced PrBa2Cu3Ox . After oxygen annealing, resistivity becomes zero below T=80 K, and zero-field-cooled magnetization shows diamagnetism with full volume fraction. X-ray energy dispersion spectrum and X-ray diffraction analyses show that this superconducting phase is orthorhombic PrBa2Cu3Ox .

http://iopscience.iop.org/article/10.1143/JJAP.36.L18/pdf

Bulk Superconductivity in Single Crystals of PrBa 2Cu 3Ox

We report on the successful growth of an isotopically enriched 28Si bulk single crystal of the size ~4 mm in diameter and ~50 mm in length. The isotopic enrichement of 28Si (99.924 at%), 29Si (0.073 at%), and 30Si (0.003 at%) has been determined by secondary-ion-mass spectroscopy (SIMS). The crystal is entirely p-type with the room temperature free-hole concentration ~ 5×1017 cm-3. The majority impurity is found to be aluminum which can be removed easily in the future zone purification process.

Growth and Characterization of the Isotopically Enriched 28Si Bulk Single Crystal

Single crystals of (NdCe)2CuO4 have been grown by the travelling-solvent floating-zone (TSFZ) method. The single crystal grown in a deoxidized atmosphere exhibits superconductivity. Part of the crystallographic phase diagram of the Nd2O3-CuO system has been derived by conventional means to determine the concentration and temperature range of the liquidus line.

Kunihiko Oka

Papers

Superconducting PrBa 2 Cu 3 O x

Phase-Equilibrium Diagram in the Ternary System Y2O3-BaO-CuO

Bulk Superconductivity in Single Crystals of PrBa 2Cu 3Ox

Growth and Characterization of the Isotopically Enriched 28Si Bulk Single Crystal

Phase Diagram and Crystal Growth of Superconductive (NdCe)2CuO4