382 research outputs found
Structure and superconductivity in the binary ReMo alloys
The binary ReMo alloys, known to cover the full range of solid
solutions, were successfully synthesized and their crystal structures and
physical properties investigated via powder x-ray diffraction, electrical
resistivity, magnetic susceptibility, and heat capacity. By varying the Re/Mo
ratio we explore the full ReMo binary phase diagram, in all its
four different solid phases: hcp-Mg (), -Mn
(), -CrFe (), and bcc-W (),
of which the second is non-centrosymmetric with the rest being centrosymmetric.
All ReMo alloys are superconductors, whose critical temperatures
exhibit a peculiar phase diagram, characterized by three different
superconducting regions. In most alloys the is almost an order of
magnitude higher than in pure Re and Mo. Low-temperature electronic
specific-heat data evidence a fully-gapped superconducting state, whose
enhanced gap magnitude and specific-heat discontinuity suggest a moderately
strong electron-phonon coupling across the series. Considering that several
-Mn-type Re alloys ( = transition metal) show time-reversal
symmetry breaking (TRSB) in the superconducting state, while TRS is preserved
in the isostructural MgIrB or NbOs, the
ReMo alloys represent another suitable system for studying the
interplay of space-inversion, gauge, and time-reversal symmetries in future
experiments expected to probe TRSB in the Re family.Comment: 8 pages, 7 figures, accepted for publication on Physical Review
Material
Cutting edge of high-entropy alloy superconductors from the perspective of materials research
High-entropy alloys (HEAs) are a new class of materials which are being
energetically studied around the world. HEAs are characterized by a
multi-component alloy in which five or more elements randomly occupy a
crystallographic site. The conventional HEA concept has developed into simple
crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc)
and hexagonal-closed packing (hcp) structures. The highly atomic-disordered
state produces many superior mechanical or thermal properties.
Superconductivity has been one of the topics of focus in the field of HEAs
since the discovery of the bcc HEA superconductor in 2014. A characteristic of
superconductivity is robustness against atomic disorder or extremely high
pressure. The materials research on HEA superconductors has just begun, and
there are open possibilities for unexpectedly finding new phenomena. The
present review updates the research status of HEA superconductors. We survey
bcc and hcp HEA superconductors and discuss the simple material design. The
concept of HEA is extended to materials possessing multiple crystallographic
sites; thus, we also introduce multi-site HEA superconductors with the
CsCl-type, {\alpha}-Mn-type, A15, NaCl-type, {\sigma}-phase and layered
structures and discuss the materials research on multi-site HEA
superconductors. Finally, we present the new perspectives of eutectic HEA
superconductors and gum metal HEA superconductors.Comment: to be published in Metal
Structure and superconductivity of tin-containing hftizrsnm (M = cu, fe, nb, ni) medium-entropy and high-entropy alloys
In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)5Sn3 partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors
Superconducting transition temperatures of the elements related to elastic constants
For a given crystal structure, say body-centred-cubic, the many-body
Hamiltonian in which nuclear and electron motions are to be treated from the
outset on the same footing, has parameters, for the elements, which can be
classified as (i) atomic mass M, (ii) atomic number Z, characterizing the
external potential in which electrons move, and (iii) bcc lattice spacing, or
equivalently one can utilize atomic volume, Omega. Since the thermodynamic
quantities can be determined from H, we conclude that Tc, the superconducting
transition temperature, when it is non-zero, may be formally expressed as Tc =
Tc^(M) (Z, Omega). One piece of evidence in support is that, in an atomic
number vs atomic volume graph, the superconducting elements lie in a well
defined region. Two other relevant points are that (a) Tc is related by BCS
theory, though not simply, to the Debye temperature, which in turn is
calculable from the elastic constants C_{11}, C_{12}, and C_{44}, the atomic
weight and the atomic volume, and (b) Tc for five bcc transition metals is
linear in the Cauchy deviation C* = (C_{12} - C_{44})/(C_{12} + C_{44}).
Finally, via elastic constants, mass density and atomic volume, a correlation
between C* and the Debye temperature is established for the five bcc transition
elements.Comment: EPJB, accepte
Investigation of superconducting interactions and amorphous semiconductors
Research papers on superconducting interactions and properties and on amorphous materials are presented. The search for new superconductors with improved properties was largely concentrated on the study of properties of thin films. An experimental investigation of interaction mechanisms revealed no new superconductivity mechanism. The properties of high transition temperature, type 2 materials prepared in thin film form were studied. A pulsed field solenoid capable of providing fields in excess of 300 k0e was developed. Preliminary X-ray measurements were made of V3Si to determine the behavior of cell constant deformation versus pressure up to 98 kilobars. The electrical properties of amorphous semiconducting materials and bulk and thin film devices, and of amorphous magnetic materials were investigated for developing radiation hard, inexpensive switches and memory elements
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