High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition ${\mathrm{Ta}}_{34}{\mathrm{Nb}}_{33}{\mathrm{Hf}}_8{\mathrm{Zr}}_{14}{\mathrm{Ti}}_{11}$ (in at. %), which possesses an average body-centered cubic structure of lattice parameter $a=3.36\AA$. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the ${\mathrm{Ta}}_{34}{\mathrm{Nb}}_{33}{\mathrm{Hf}}_8{\mathrm{Zr}}_{14}{\mathrm{Ti}}_{11}$ HEA is a type II superconductor with a transition temperature $T_c\approx 7.3\mathrm{K}$, an upper critical field ${\mu }_0{H}_{c2}\approx 8.2\mathrm{T}$, a lower critical field ${\mu }_0{H}_{c1}\approx 32\mathrm{mT}$, and an energy gap in the electronic density of states (DOS) at the Fermi level of $2\mathrm{\Delta }\approx 2.2\mathrm{meV}$. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a “dirty” superconductor. We show that the lattice degrees of freedom obey Vegard’s rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a “cocktail” of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable.

We report on the discovery of a high-entropy alloy (HEA) with a hexagonal crystal structure. Equiatomic samples in the alloy system Ho–Dy–Y–Gd–Tb were found to solidify as homogeneous single-phase HEAs. The results of our electron diffraction investigations and high-resolution scanning transmission electron microscopy are consistent with an Mg-type hexagonal structure. The possibility of hexagonal high-entropy alloys in other alloy systems is discussed.

Bulk samples of Pd41Ni10Cu29P20 glass were tested at constant true stress (20–636MPa) in compression at 550, 555, and 565K to study the transition from steady-state creep at low stress to deformation-induced softening at high stress. In the high-stress regime strongly accelerating creep was observed. All deformation was homogeneous. The activation volume was 106Å3. The isoconfigurational activation energy was 9.03±0.64eV. The disordering rate is proportional to the applied power density (stress×strain rate). The disordering process is inefficient in energy and in the production of free volume.

For the first time quasicrystal surfaces produced by in situ cleavage in ultrahigh vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster aggregates formed on the basis of an elementary cluster whose contrast behavior and diameter of about 1 nm point to the Mackay-type cluster. Crack propagation occurs along zones of lower strength between clusters. This supports the cluster approach to quasicrystal structure.