Effects of pressure on tiny antiferromagnetic moments in the heavy-electron compound URu2Si2 Amitsuka, H.; Sato, M.; Metoki, N.; Yokoyama, M.; Kuwahara, K.; Sakakibara, T.; Morimoto, H.; Kawarazaki, S.; Miyako, Y.; Mydosh, J.A.

No abstract

Crystallization of an amorphous solid is usually accompanied by a significant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the importance of crystalline order for the transport of charge and heat. Phase-change materials, however, reveal a remarkably low thermal conductivity in the crystalline state. The small change in this conductivity upon crystallization points to unique lattice properties. The present investigation reveals that the thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These fi ndings are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time.

The deformation behavior of the surrounded Cu stabilized YBCO coated conductor based on the Hastelloy substrate and its influence on the critical current were precisely investigated. The mechanical properties were assessed at room temperature and 77 K. The greatest contribution was brought by two metallic components of the Hastelloy substrate and Cu stabilized layers. The internal strain exerted on the superconducting YBCO layer was determined directly by using synchrotron radiation facilities. The thermally induced residual strain with compressive component decreased during the tensile loading and changed to a tensile component at the force free strain (Aff), at which the internal stress becomes zero in the YBCO layer. Beyond Aff, the increasing rate of internal strain slowed down, suggesting brittle behavior, that is, the formation of micro-cracks. The applied strain dependence of the critical current could be divided into two regions. In the reversible region, the strain dependence obeyed the intrinsic strain effect and was well expressed by the Ekin formula. Beyond the reversible limit, the critical current decreased rapidly with strain. The degradation is suggested to be attributed to the formation of cracks in the YBCO layer. The force free strain evaluated from the mechanical properties was 0.26%. On the other hand, the strain at the critical current maximum was observed to be 0.035–0.012%. These facts suggest re-examining the hypothesis supposing that the critical current maximum appears at the force free strain in YBCO coated conductors.

A method to estimate the thermally induced residual strain accumulation under varying temperature in a Bi2223/Ag/Ag alloy composite superconductor was presented, in which the mechanical property values measured from the stress-strain curves of the samples with different residual strain states, the residual strain value of Bi2223 filaments in the composite tape at room temperature measured by x-ray diffraction and the reported coefficients of thermal expansion of the constituents (Bi2223, Ag and Ag alloy) in the relevant temperature range were incorporated. This method was applied to estimate the change of the residual strain of all constituents of the high critical current type composite tape fabricated by American Superconductor Corporation as a function of temperature. The residual strain value at 77 K estimated by this method and the reported fracture strain of Bi2223 filaments accounted well for the measured strain tolerance of the critical current at 77 K.