Hideaki Hikosaka

Yield properties, phase transition, and equation of state of aluminum nitride (AlN) under shock compression up to 150 GPa

Inclined-mirror Hugoniot measurements were performed on pure AlN polycrystals in the pressure range up to 150 GPa to study the yield properties, phase transition, and equation of state. The Hugoniot-elastic limit (HEL) stress was approximately 9.4 GPa. Above the HEL, the Hugoniot data converged to a static compression curve despite the high thermal conductivity, which indicated that the thermal property is not an important factor in determining the shock yield property. The phase transformation from wurtzite-type (B4) to rock salt-type (B1) structure took place at approximately 19.4 GPa, and was completed by about 75 GPa. The corrected transition pressure at 298 K was 19.2 GPa. Shock velocity (Us) versus particle velocity (Up) relation of the final phase was given by Us=3.27+1.81Up km/s. The Birch–Murnaghan fitting curve of the calculated isothermal compression curve of the B1-type phase roughly coincided with the recent static x-ray diffraction data up to over 100 GPa. The Gruneisen parameter, bulk modul...

Oriented Bulk Consolidation of Bi–Sr–Ca–Cu–O by Shock-Loading Method

Shock compaction experiments were carried out for Bi2Sr2CaCu2Oy particles sorted to 46–74 µ m and packing density of 50–82% at a shock pressure of 8 GPa. Bulk density reached 95% by shock compaction independent of the porosity. The most effective orientation was achieved by shock loading for the packing density of 67% and with post annealing at 870°C. The texture of the shocked plus postannealed specimen showed crystal growth not only within the c-plane but also along the c-axis. The Meissner volume fraction of the shock compacted specimen decreased with decreasing packing density but the onset temperature did not change. The magnetic torque of shock plus annealed specimen showed the alignment of particles.

Characterization of grain-structure in shocked YBCO particles

Abstract Fine YBCO powders were shock-compacted at around 5 GPa using a propellant gun. Shock-compacted pellets have large grains of 5–25 μm in length with large growth-steps caused mainly by heats generated in a shock-loading.

Shock-synthesis of a metastable tetragonal phase of EuBa2Cu3Oy

Shock-synthesized EuBa2Cu3Oy was found to be a metastable tetragonal phase with c/a=3.00, which is only obtainable at relatively low temperatures by conventional solid state reactions. The annealing of the shock-synthesized phase above 900 °C and subsequent oxidation lead to superconduction together with the increase in the c/a ratio to 3.05, presumably due to formation of perfect ordering of Eu and Ba atoms. These results suggest that no complete ordering between Eu and Ba, hence incomplete formation of CuO2 plane necessary for superconduction, would be established during a short time interval of shock synthesis process.

Magnetic Torque of Oriented Bulk Bi-Sr-Ca-Cu-O by Shock-Loading Method

Crystalline orientation and flux pinning of oriented bulk specimen of Bi2Sr2CaCu2O8+δ (Bi2212) and Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi2223) prepared by the shock loading method were investigated by the magnetic torque measurement under magnetic fields up to 8 kOe in the temperature range from 4.2 to 100 K. In the case of Bi2212, the angular dependence of the torque, was reproduced by assuming the Gauss-type distribution for the crystalline orientation. It became clear that the magnetic torque of the shocked specimen showed the high degree of crystalline orientation in which the c-a.xis is perpendicular to the pellet disk plane and that the flux pinning perpendicular to the pellet disk plane was enhanced by shock-loading.

Characterization of EuBa2Cu3Oy Synthesized in Shock Processes

We synthesized a homogeneous, tetragonal EuBa2Cu3Oy with c/a=3.00 by the shock compression method. The phase is considered to be similar to the tetragonal YBa2Cu3Oy metastably formed at relatively low temperature with the c/a ratio=3.00. Electron diffraction patterns indicate ordering of Eu and Ba atoms to some extent, but ordering is presumably not perfect. High resolution trasmission electron microscory images show that shock-synthesized EuBa2Cu3Oy consists of 60-80-A-size domains, whose principal axes are perpendicular to each other. Perfect ordering of Eu and Ba atoms was achieved by annealing the shock-synthesized specimen above 900° C, resulting in the increase of the c/a ratio from 3.00 to 3.05 as well as superconduction upon O2 annealing. This result is explained by the shortness of the reaction time in shock processes.