Hydrostatic Compression Effects on Fifth-Group Element Superconductors V, Nb, and Ta Subjected to High-Pressure Torsion

Abstract

In fifth-group element superconductors V, Nb, and Ta, the increase in superconducting transition temperature (T c) was attempted by using both high-pressure torsion (HPT) and additional hydrostatic pressure (HP) compression. The former brings about the grain refinement and strain accumulation in the unit-cell level. The additional compression for severely strained superconductors triggers strengthening intergrain-contact and/or structural deformation in the unit-cell level. The manner of the appearance of the above two effects depends on the kind of elements: First, in V, there is no prominent effect of HPT, comparing to the hydrostatic compression effects on its non-strained material. Next, in Ta, the effect of strengthening intergrain-contact appears at small hydrostatic compression, resulting in temporal increase in T c. Finally, Nb exhibits prominent increase in T c by both effects and, in particular, the structural deformation in the unit-cell level promotes the increase in T c. Thus, the accumulation of residual strain in the level of starting material can be a promising work to manipulate T c under HP compression.

High pressure studies of the T−P phase diagrams of erbium and thulium up to 30 GPa by using ac magnetization experiments

“…Therefore with increasing the frequency of H ac , the intensity of background signal increases and broad humps appear over a wider temperature range. Indeed, most of the metallic background contributions appeared in m (out of phase for H ac ), while the magnetic signal of Er and Tm mainly appeared in m (in phase for H ac ) [37,[40][41][42][43][44][45][46][47]. Even if utilizing favorable phase separation, in the M ac measurement using DAC, discerning between the two anomalies for Er and Tm is more challenging because of small T N signal, compared to previous experiments involving Gd-Ho [11].…”

Advanced Photocatalysts for CO2 Conversion by Severe Plastic Deformation (SPD)

“…The SPD field experienced significant progress in the past three decades, as discussed in several review papers [ 124 , 125 , 126 , 127 , 128 , 129 ], and more recently in a special issue in 2019 [ 130 ], which gathered overviews on both historical developments [ 131 ] and recent advancements [ 132 ]. A survey of these overviews indicates that despite significant progress on theoretical aspects [ 133 , 134 ], mechanisms [ 135 , 136 ], processing [ 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 ], microstructure [ 145 , 146 , 147 , 148 , 149 ], and mechanical properties [ 150 , 151 , 152 , 153 , 154 , 155 ] of metallic materials, there is a recent tendency to apply SPD to a wider range of materials (oxides [ 156 ], semiconductors [ 157 ], carbon polymorphs [ 158 ], glasses [ 159 ], and polymers [ 160 ]) to control phase transformations [ 161 ] and solid-state reaction [ 162 , 163 , 164 ] for achieving advanced functional properties [ 165 , 166 , 167 , 168 , 16...…”

Superconductivity of barium with highest transition temperatures in metallic materials at ambient pressure

“…Herein, the compressive stress allows only the diagonal components in the strain tensor, whereas the shear strain leads to the nondiagonal components and plays an imperative role in generating possible crystal structures that realize a strain-induced superconducting state. In earlier studies, HPT processing of Re 21 and Nb 22 – 24 stabilized the superconductivity, and the increase in T c for Re was due to the increase of the density of states (DOS) at the Fermi level with the expansion of the unit cell volume 21 , and that for Nb also to the DOS increase with the deformation of the unit cell 22 – 24 . In general, shear strain is known to introduce not only such simple structural deformations but also an accumulation of dislocations and leads to the formation of a fine-grained structure, resulting in a long-lived quasi-stable state even after releasing stress 25 , 26 .…”