Electronic transport properties of the Al0.5TiZrPdCuNi alloy in the high-entropy alloy and metallic glass forms

High-entropy alloys (HEAs) are characterized by a simultaneous presence of a crystal lattice and an amorphous-type chemical (substitutional) disorder. In order to unravel the effect of crystal-glass duality on the electronic transport properties of HEAs, we performed a comparative study of the electronic transport coefficients of a 6-component alloy Al0.5TiZrPdCuNi that can be prepared either as a HEA or as a metallic glass (MG) at the same chemical composition. The HEA and the MG states of the Al0.5TiZrPdCuNi alloy both show large, negative-temperature-coefficient resistivity, positive thermopower, positive Hall coefficient and small thermal conductivity. The transport coefficients were reproduced analytically by the spectral conductivity model, using the Kubo-Greenwood formalism. For both modifications of the material (HEA and MG), contribution of phonons to the transport coefficients was found small, so that their temperature dependence originates predominantly from the temperature dependence of the Fermi-Dirac function and the variation of the spectral conductivity and the related electronic density of states with energy within the Fermi-level region. The very similar electronic transport coefficients of the HEA and the MG states point towards essential role of the immense chemical disorder

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

Principle of work of the vortex heat generator installation

Представленная статья содержит краткий анализ вихревых теплогенерирующих установок (ВТУ), обзор актуальности темы исследования, патентноинформационное обоснование, а также проанализированы современные научнообоснованные факты и результаты, как теоретических, так и экспериментальных работ. Исследованы основные основополагающие (физико-химические, технологические процессы, технико-экономические и законодательные обоснования), а также и другие актуальные вопросы касательно ВТУ. The presented article contains a brief analysis of vortex heat-generating plants, an overview of the relevance of the research topic, patent information justification, and also analyzes modern scientifically-based facts and results of both theoretical and experimental work. The basic fundamental (physicochemical, technological processes, feasibility and legislative justifications), as well as other relevant issues regarding vortex heat-generating installations are investigated

Dipolar spin ice states with a fast monopole hopping rate in CdEr2X4 ( X=Se , S)

Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr 2 Se 4 is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy 2 Ti 2 O 7 . In this Letter we use diffuse neutron scattering to show that both CdEr 2 Se 4 and CdEr 2 S 4 support a dipolar spin ice state—the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy 2 Ti 2 O 7 , i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er 3 + ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr 2 X 4 ( X = Se , S) are primarily due to much faster monopole hopping. Our work suggests that CdEr 2 X 4 offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples

Magnetic properties of FeAl(2) and Fe(2)Al(5)

We have investigated magnetic properties of the FeAl2 and Fe2Al5 intermetallic compounds. By measuring the zero-field-cooled and field-cooled static (dc) magnetic susceptibilities in low and high magnetic fields, the frequency-dependent (ac) susceptibility, the magnetization versus the magnetic field, and the thermoremanent magnetization time decay, we found that the magnetic structures of FeAl2 and Fe2Al5 are richer than those published so far in the literature. FeAl2 undergoes complex two-step magnetic ordering. At T approximate to 32 K, a magnetic phase transition (not yet specified) takes place in which a small fraction of the Fe spins participate, whereas at T-f2 approximate to 12 K, the majority spin fraction undergoes a spin-freezing transition to a spin glass phase. Fe2Al5 undergoes a transition to a spin glass phase at the spin freezing temperature T-f approximate to 3 K, which was not reported previously. The spin glass phase in Fe2Al5 is "soft" and fragile with respect to the external magnetic field and can only be observed in low magnetic fields below similar to 100 Oe. The origins of the spin glass ordering in the FeAl2 and Fe2Al5 phases are randomness and frustration that are present on the Fe sublattices of both compounds. In FeAl2, the Fe spins are positioned randomly on the three mixed-occupation Al/Fe sites of the unit cell, whereas in Fe2Al5, partial occupation of the Fe-neighboring Al2 and Al3 atomic sites imposes different degrees of Fe moment screening by the electron cloud, resulting in a random distribution of the magnetic moment sizes. Geometric frustration because of positioning of the antiferromagnetically coupled Fe spins on triangles is present in both compounds as well

Mechanochemically assisted solid-state and citric acid complex syntheses of Cu-doped sodium cobaltite ceramicsh

In the last decade, the sodium cobaltite ceramic became a promising candidate for potential thermoelectric applications, because of its large thermopower and low resistivity. In this work, polycrystalline samples of NaCo(2-x)CuxO(4) (x = 0, 0.01, 0.03, 0.05) were prepared using mechanochemically assisted solid-state reaction method (MASSR) and the citric acid complex method (CAC). Bulk samples were prepared by pressing into disc-shaped pellets and subsequently subjected to a thermal treatment at 880 degrees C in inert argon atmosphere. Changes in structural and microstructural characteristics of the samples, caused by the substitution of Cu for Co, were characterized using X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM), respectively. The results of inductively coupled plasma (ICP) analysis showed that the compositions of the final products correspond to gamma-NaCo2O4 and confirmed that desired compound was obtained in both syntheses procedures. The advantages and disadvantages of these two syntheses procedures have been observed and discussed: the CAC method enabled obtaining samples with higher density and fine microstructure compared to the MASSR method, thus better thermoelectric properties. The Cu2+ substitution led to the increase in Seebeck coefficient in both synthesis routes. The highest figure of merit of 0.022 at 300 K was observed for the sample doped with 1 mol% Cu, obtained by the CAC method, and it was almost twice higher than in the undoped sample confirming the significant influence of Cu-doping with even small concentrations

Superconductivity in thermally annealed Ta-Nb-Hf-Zr-Ti high-entropy alloys

We present a study of superconductivity in Ta-Nb-Hf-Zr-Ti high-entropy alloys (HEAs) by investigating four samples of different atomic concentrations (equimolar and off-equimolar) and number of components (4 and 5), subjected to different thermal treatments. The structure of the samples varied between a homogeneous random solid solution and a partially ordered nanostructure in the form of a three-dimensional grid of short-range ordered atomic clusters enriched in Zr and Hf that has developed during long-time annealing. Superconductivity was found to be a robust phenomenon, being quite insensitive to the actual structure of the material. All investigated samples were superconducting in the entirety of their volumes. The superconducting transition temperatures TC of the samples are scattered in the range between 5.0 and 7.3 K and this scatter could be related to the degree of structural and chemical inhomogeneity of the samples. In the samples with partially ordered nanostructure, short-range atomic clusters possess a slightly different TC than the Ta- and Nb-rich matrix. Our results also demonstrate the important fact that the formation, stability and structure of a regular (non-ideal) HEA mixture are determined by both, the minimization of the mixing enthalpy that favors local atomic ordering and the maximization of the mixing entropy that favors a random solid solution. The actual equilibrium state achieved during long-time thermal annealing via the atomic diffusion is generally partially ordered, and the resulting nanostructure is a sensitive function of the number of components constituting the HEA, their concentrations, the differences in the atomic radii and the annealing temperature and time. This nanostructure essentially determines the electronic properties of HEA materials