Superconductivity in a new hexagonal high entropy alloy

High entropy alloys (HEAs) are the new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal close-packed (hcp) structure are highly desirable in connection to their in general high hardness. Herein, we report the synthesis, structure and detailed superconducting properties of Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$-the first hexagonal superconducting high entropy alloy (HEA) composed of five randomly distributed transition-metals. Combination of room temperature precession electron diffraction, precession electron diffraction tomography and powder X-ray diffraction is utilized to determine the room temperature crystal structure. Transport, magnetic and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at $T_{c}$ = 4.4 K, lower critical field $H_{c1}$(0) = 2.3 mT and upper critical field $H_{c2}$(0) = 3.6 T. Low-temperature specific heat measurement indicates that Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$ is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific heat jump $\frac{\Delta C_{el}}{\gamma_{n}T_{c}}$ = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and $T_{c}$ follows crystalline-like behaviour.Comment: 6 Pages, 9 Figures. arXiv admin note: text overlap with arXiv:1804.1009

Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO4_4

Geometrically frustrated structures combined with competing exchange interactions that have different magnitudes are known ingredients for achieving exotic properties. Herein, we studied detailed structural, magnetic, thermal (specific heat), magneto-dielectric, and magnetic exchange bias properties of a mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed magnetization, heat capacity, and neutron powder diffraction studies (NPD) highlight long-range ferrimagnetic ordering with an onset at 355 K. The magnetic structure is established using a ferrimagnetic model (collinear-type) that has a propagation vector k = 0, 0, 0. The magneto-dielectric effect appears below the magnetic ordering temperature, and the exchange bias (EB) effect is observed in field cooled (FC) conditions below 355 K. The magneto-dielectric coupling in CoFeRhO$_4$ originates due to the frustration in the structure, collinear ferrimagnetic ordering, and uncompensated magnetic moments. The unidirectional anisotropy resulting from the uncompensated magnetic moments causes the room-temperature exchange bias effect. Remarkably, the appearance of technologically important properties (ferromagnetism, magnetodielectric effect, and EB) at room temperature in CoFeRhO$_4$ indicates its potential use in sensors or spintronics.Comment: 8 pages, 11 Figure

Electron doping and phonon scattering in Ti1+xS2 thermoelectric compounds

Bulk polycrystalline samples in the series Ti1+xS2 (x = 0 to 0.05) were prepared using high temperature synthesis from the elements and spark plasma sintering. X-ray structure analysis shows that the lattice constant c expands as titanium intercalates between TiS2 slabs. For x=0, a Seebeck coefficient close to -300 μV/K is observed for the first time in TiS2 compounds. The decrease in electrical resistivity and Seebeck coefficient that occurs upon Ti intercalation (Ti off stoichiometry) supports the view that charge carrier transfer to the Ti 3d band takes place and the carrier concentration increases. At the same time, the thermal conductivity is reduced by phonon scattering due to structural disorder induced by Ti intercalation. Optimum ZT values of 0.14 and 0.48 at 300K and 700K, respectively, are obtained for x=0.025

Ordering process and ferroelectricity in a spinel derived from FeV2O4

The spinel FeV2O4 is known to exhibit peculiar physical properties, which is generally ascribed to the unusual presence of two cations showing a pronounced interplay between spin, orbital and lattice degrees of freedom (Fe2+ and V3+ on the tetrahedral and octahedral sites, respectively). The present work reports on an experimental re-investigation of this material based on a broad combination of techniques, including x-ray diffraction, energy dispersive and M\"ossbauer spectroscopies, as well as magnetization, heat capacity, dielectric and polarization measurements. Special attention was firstly paid to establish the exact cationic composition of the investigated samples, which was found to be Fe1.18V1.82O4. All the physical properties were found to point out a complex ordering process with a structural transition at TS = 138 K, followed by two successive magnetostructural transitions at TN1 = 111 K and TN2 = 56 K. This latter transition marking the appearance of electric polarization, magnetization data were analysed in details to discuss the nature of the magnetic state at T< TN2. An overall interpretation of the sequence of transitions was proposed, taking into account two spin couplings, as well as the Jahn-Teller effects and the mechanism of spin-orbit stabilization. Finally, the origin of ferroelectricity in Fe1.18V1.82O4 is discussed on the basis of recent models.Comment: 26 pages, 9 figures,59 references.Accepted by Physical Review

Development and evaluation of real time RT-PCR assays for detection and typing of Bluetongue virus

Bluetongue virus is the type species of the genus Orbivirus, family Reoviridae. Bluetongue viruses (BTV) are transmitted between their vertebrate hosts primarily by biting midges (Culicoides spp.) in which they also replicate. Consequently BTV distribution is dependent on the activity, geographic distribution, and seasonal abundance of Culicoides spp. The virus can also be transmitted vertically in vertebrate hosts, and some strains/serotypes can be transmitted horizontally in the absence of insect vectors. The BTV genome is composed of ten linear segments of double-stranded (ds) RNA, numbered in order of decreasing size (Seg-1 to Seg-10). Genome segment 2 (Seg-2) encodes outer-capsid protein VP2, the most variable BTV protein and the primary target for neutralising antibodies. Consequently VP2 (and Seg-2) determine the identity of the twenty seven serotypes and two additional putative BTV serotypes that have been recognised so far. Current BTV vaccines are serotype specific and typing of outbreak strains is required in order to deploy appropriate vaccines. We report development and evaluation of multiple ‘TaqMan’ fluorescence-probe based quantitative real-time type-specific RT-PCR assays targeting Seg-2 of the 27+1 BTV types. The assays were evaluated using orbivirus isolates from the ‘Orbivirus Reference Collection’ (ORC) held at The Pirbright Institute. The assays are BTV-type specific and can be used for rapid, sensitive and reliable detection / identification (typing) of BTV RNA from samples of infected blood, tissues, homogenised Culicoides, or tissue culture supernatants. None of the assays amplified cDNAs from closely related but heterologous orbiviruses, or from uninfected host animals or cell cultures

Evolution and Phylogenetic Analysis of Full-Length VP3 Genes of Eastern Mediterranean Bluetongue Virus Isolates

Bluetongue virus (BTV) is the ‘type’ species of the genus Orbivirus within the family Reoviridae. The BTV genome is composed of ten linear segments of double-stranded RNA (dsRNA), each of which codes for one of ten distinct viral proteins. Previous phylogenetic comparisons have evaluated variations in genome segment 3 (Seg-3) nucleotide sequence as way to identify the geographical origin (different topotypes) of BTV isolates. The full-length nucleotide sequence of genome Seg-3 was determined for thirty BTV isolates recovered in the eastern Mediterranean region, the Balkans and other geographic areas (Spain, India, Malaysia and Africa). These data were compared, based on molecular variability, positive-selection-analysis and maximum-likelihood phylogenetic reconstructions (using appropriate substitution models) to 24 previously published sequences, revealing their evolutionary relationships. These analyses indicate that negative selection is a major force in the evolution of BTV, restricting nucleotide variability, reducing the evolutionary rate of Seg-3 and potentially of other regions of the BTV genome. Phylogenetic analysis of the BTV-4 strains isolated over a relatively long time interval (1979–2000), in a single geographic area (Greece), showed a low level of nucleotide diversity, indicating that the virus can circulate almost unchanged for many years. These analyses also show that the recent incursions into south-eastern Europe were caused by BTV strains belonging to two different major-lineages: representing an ‘eastern’ (BTV-9, -16 and -1) and a ‘western’ (BTV-4) group/topotype. Epidemiological and phylogenetic analyses indicate that these viruses originated from a geographic area to the east and southeast of Greece (including Cyprus and the Middle East), which appears to represent an important ecological niche for the virus that is likely to represent a continuing source of future BTV incursions into Europe