Shoji Miyashita

Synthesis of superconducting Pb‐doped HgBa2CaCu2Oy films by laser ablation and post‐annealing

Superconducting Pb‐doped HgBa2CaCu2Oy films have been successfully synthesized on the (100) SrTiO3 substrate by laser ablation using a Pb‐doped Hg‐1212 target and post‐annealing. The as‐deposited film was post‐annealed with a pellet of the same powders as those of the target at 760 °C for 20 min in an evacuated quartz tube. The obtained film exhibited the (00n) oriented x‐ray diffraction pattern of the Hg‐1212. The superconducting transition temperature, Tczero, was 117 K. Anisotropy of magnetization, M(T) and M‐H curves in the directions of two different fields was confirmed.

The Structure and Superconducting Properties of Multifilamentary Nb3Sn Wires Prepared by Internal Sn Diffusion Process Using Sn-Ti Cores

The multifilamentary Nb3Sn superconducting wires with the titanium addition have been fabricated by internal tin diffusion process to improve critical current density (J) at high fields (>12T). The wires fabricated have seven modules in a copper matrix. The module is composed of the Sn-2wt%Ti alloy core instead of the tin core at the center and 90 niobium filaments located by three layers around the Sn-Ti core.

Improvements in critical current densities of internal tin diffusion process Nb 3 Sn wires by additions of third elements

Improvements in critical current densities of internal tin diffusion process Nb 3 Sn multifilamentary wires have been attempted by indium and titanium additions. The Nb 3 Sn wires with the indium addition to the Sn core and the titanium addition to the Cu matrix have been fabricated. The indium addition increases critical current density (Jc) at each field compared with pure Nb 3 Sn wire, and Jc at higher fields increases with increasing filament diameter. An overall Jc of 6.2 × 104A/cm2at 12T and 4.2K is obtained for the 4.2 μm-filament indium addition wire reacted at 750 °C-50h. The titanium addition increases the Nb 3 Sn layer growth rate and Jc in fields over 13T. An overall Jc of 3.0 ×104A/cm2at 15T and 4.2K is obtained for the 11.7 μm-filament titanium addition wire. Moreover, the simultaneous indium addition to the titanium addition wire produces further improvement in Jc. The indium and titanium addition Nb 3 Sn wires are the most favorable superconductors for generating magnetic field over 10T.

Characterization of LiNb1-xTaxO3 composition-spread thin film by the scanning microwave microscope

Dielectric property of a composition-spread LiNb 1-x Ta x O 3 thin film, fabricated by the combinatorial pulsed-laser deposition (PLD) method, was systematically characterized by the scanning microwave microscope (SμM). Measured frequency shift showed a broad maximum around x = 0.2-0.5, and gradually decreased with x, resulting in a lower dielectric constant in the LiTaO 3 side compared to the LiNbO 3 side. The trend of frequency shift has been revealed to possess a strong correlation with the sharpness of XRD peak, suggesting that lowering of dielectric constant is principally brought about by the degradation of crystallinity.

High pressure synthesis and magnetic properties for Hg1−xRexBa2Ca2Cu3Oy

Abstract Hg 1− x Re x Ba 2 Ca 2 Cu 3 O y samples with a nominal composition of x =0, 0.1 and 0.2 were synthesized at a high pressure from the powders of raw materials without calcination. We investigated the influence of the nominal Re content ( x ) and the nominal oxygen content ( y ) on the crystallization, critical temperature and magnetic properties. Almost a single phase of Hg-1223 was obtained in the range 0≤ x ≤0.1. The substitution of Re for Hg caused a decrease of T c mag . The lattice parameter ratio ( c / a ) of the Re-substituted samples was smaller than that for the non-substituted samples. The intragrain J c values at B ≤5 T for the Re-substituted samples were higher than those for the non-substituted samples at 60–100 K. The irreversibility field ( B irr ) at J c =1000 A/cm 2 was improved by Re substitution at 80–100 K. The post oxygenation of our samples was less effective in increasing B irr . This was probably due to Hg depletion during oxygenation.

Fabrication of Bi-La-Sr-Mn-O uncooled microbolometer

Since perovskite manganese oxide Bi–La–Sr–Mn–O (BLSMO) has a large temperature coefficient of resistance (TCR: defined as 1/R dR/dT) of above 3%/K, it has been considered to be a suitable candidate for use as an uncooled IR bolometer material. We fabricated a single pixel device of the BLSMO microbolometer and evaluated it. The BLSMO film was deposited by RF magnetron sputtering at ambient temperature in an oxygen atmosphere. The film showed the TCR of 3.1%/K at room temperature. The size of the single pixel device is 38×38 µm2. To achieve high infrared absorption, the detector contains an infrared absorbing membrane with a high fill factor of 90%. In a vacuum, the detector showed a thermal conductance of 1.3×10-7 W/K and a responsivity of 4.8×105 V/W. According to these numerical values, a noise equivalent temperature difference (NETD) of the BLSMO microbolometer was estimated as being about 0.1 K with f/1.0 optics.

Structure and Superconducting Properties of HgBa2CaCu2Oy Films Prepared by Laser Ablation

Hg-1212 films were prepared on the (100) SrTiO3 substrate by laser ablation and subsequent annealing. The as-grown film was annealed with a Hg-1212 bulk pellet in a quartz tube. The superconducting transition temperature T c(onset) was 123 K and T c(ρ=0) was 97 K. This film was shown to have a preferential orientation of the c-axis perpendicular to the (100) SrTiO3 substrate, and was composed of Hg-1212 platelike grains and Ba–Cu–O compounds.

Effects of titanium addition to the Nb 3 Sn wires fabricated by the internal tin diffusion process

The titanium-doped Nb 3 Sn wires have been successfuly fabricated by the internal tin diffusion process (IDP). These wires consist of a Sn-4.8 at%Ti alloy core at the center and 99 pure niobium and/or Nb-1.9at%Ti alloy filaments placed in three layers around the Sn-Ti core. These wires were easily drawn to the final sizes without any intermediate annealing, and were heat treated at 650-750°C for 30 - 300 hr. The Electron Probe Micro Analysis analysis (EPMA) has revealed that, when the titanium is added only to the tin core, the titanium content in Nb 3 Sn filaments decreases with increasing distance from the center of the wire. On the other hand, the simultaneous titanium addition to the tin core and two outer layers of niobium filaments has attained the uniformity of the titanium content; ∼ 0.8at%Ti is incorporated in all Nb 3 Sn filaments. The overall J c of \sim 4 \times 10^{4} A/cm2at 15 T and the improved B c2 have been obtained for the Nb 3 Sn wires with the simultaneous titanium addition. These results indicate that the IDP Nb 3 Sn wires with simultaneous titanium addition to the tin core and niobium filaments are the most promising candidate materials for high field magnets.

The Superconducting Properties for La–Sr–Cu–O Systems

Superconducting oxides, La–Sr–Cu–O and Y–Ba–Cu–O were prepared using nitrate mixture by spray dry method and/or oxide and carbonate powder mixtures followed by pressing and sintering. The superconducting properties such as critical temperature (Tc) and critical current density (Jc) were measured by resistive and inductive methods, and transport current and magnetization measurements, respectively. The Tcs(the resistive offset) were 32, 91 K for La and Y system, respectively. The Jc(77K) of 1,840 A/cm2 was observed for Y system by transport current measurement.

YBa2Cu3O7 growth on metal substrates with SrTiO3 buffer layer by metal-organic chemical vapor deposition

We prepared oxide superconducting YBa2Cu3O7-x thin films on Hastelloy substrates with a SrTiO3 buffer layer by metal-organic chemical vapor deposition (MOCVD) using a single source of tetrahydrofuran solution. To clarify the cause of poor superconducting properties, the cross section of YBa2Cu3O7-x/SrTiO3/Hastelloy was examined by TEM. The YBa2Cu3O7-x and SrTiO3 layers grew perpendicular to the Hastelloy surface, which was columnar. The orientation of the YBa2Cu3O7-x layer seems to depend on that of the SrTiO3 layer. As a result, it is considered that the deposition of a good single-crystalline buffer layer on Hastelloy is the most important factor for obtaining excellent YBa2Cu3O7-x films.