Transition Metal Tellurides Research Articles

Ferrimagnetic Co1+δTe nanostructures

Transition metal telluride, Co1+δTe nanostructures are synthesized using the hydrothermal method. These nanostructures exhibit filled NiAs-type hexagonal crystal structure also known as Ni2In structure with the space group p63/mmc. The Co1+δTe nanostructures exhibit hard ferrimagnetic behavior below 40 K. The coercivity increases with the decrease in temperature, which is around 4.90 kOe at 3 K. The saturation magnetization is 0.6 μB/Co atom. Electrical transport measurements show that the Co1+δTe nanostructures are nonmetallic in nature with the resistance increases with the decrease in temperature. It does not follow the thermal excitation law for semiconductors, but can be explained by the Motts three-dimensional variable range hopping model.

Pressure-driven superconductivity in the transition-metal pentatellurideHfTe5

Layered transition-metal tellurides have attracted considerable attention because of their rich physics; for example, tungsten ditelluride WTe2 exhibits extremely large magnetoresistance; the tritelluride ZrTe3 shows a charge density wave transition at low temperature; and the pentatelluride ZrTe5 displays an enigmatic resistivity anomaly and large thermoelectric power. Recently some transition-metal tellurides are predicted to be quantum spin Hall insulators (e.g. ZrTe5 and HfTe5) or Weyl semimetals (e.g. WTe2 and MoTe2) and were subjected to intensive investigations. Here, we report on the discovery of superconductivity in hafnium pentatelluride HfTe5 under high pressure. We observe two structural phase transitions and metallization with superconductivity developing at around 5 GPa. A maximal critical temperature of 4.8 K is attained at a pressure of 20 GPa, and superconductivity persists up to the maximum pressure in our study (42 GPa). Theoretical calculations indicate that the superconductivity develops mainly in the Te atom layers at medium pressure and in the Te atom chains at high pressure.

Iron Telluride-Decorated Reduced Graphene Oxide Hybrid Microspheres as Anode Materials with Improved Na-Ion Storage Properties.

Transition-metal telluride materials are studied as the anode materials for Na-ion batteries (NIBs). The FeTe2-reduced graphene oxide (rGO) hybrid powders (first target material) are prepared via spray pyrolysis and subsequent tellurization. The H2Te gas treatment transforms the Fe3O4-rGO powders to FeTe2-rGO hybrid powders with FeTe2 nanocrystals (various sizes <100 nm) embedded within the rGO. The FeTe2-rGO hybrid powders contain 5 wt % rGO. The Na-ion storage mechanism for FeTe2 in NIBs is described by FeTe2 + 4Na(+) + 4e(-)↔Fe + 2Na2Te. The FeTe2-rGO hybrid discharge process forms metallic Fe nanocrystals and Na2Te by a conversion reaction of FeTe2 with Na ions. The discharge capacities of the FeTe2-rGO hybrid powders for the first and 80th cycles are 493 and 293 mA h g(-1), respectively. The discharge capacities of the bare FeTe2 powders for the first and 80th cycles are 462 and 83 mA h g(-1), respectively. The FeTe2-rGO hybrid powders have superior Na-ion storage properties compared to bare FeTe2 powders owing to their high structural stability and electrical conductivity.

Electrical transport and magnetic properties of cobalt telluride nanostructures

Transition metal telluride CoTe nanostructures have been synthesized using a wet-chemical method. These nanostructures exhibit NiAs-type hexagonal crystal structure with a space group of P63/mmc. The magnetic measurements show spontaneous magnetization and hysteresis, and the coercivity increases with a decrease in temperature. The saturation magnetization was calculated to be around 0.2 μB/Co atom. The magnetic transition temperature was found to be above room temperature similar to that of the bulk CoTe. The measured bandgap of the nanostructures is 2.15 eV and they exhibit p-type semiconducting behavior.

Extremely large and significantly anisotropic magnetoresistance in ZrSiS single crystals

Recently, the extremely large magnetoresistance (MR) observed in transition metal telluride, like WTe2, attracted much attention because of the potential applications in magnetic sensor. Here, we report the observation of extremely large magnetoresistance as 3.0 × 104% measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (∼1.4 × 104%) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the magnetic sensors.

Multiband superconductivity in Ta4Pd3Te16 with anisotropic gap structure

We carried out measurements of the magnetoresistance, magnetic susceptibility and specific heat on crystals of the low-dimensional transition metal telluride Ta4Pd3Te16. Our results indicate that Ta4Pd3Te16 is an anisotropic type-II superconductor in the clean limit with the extracted Ginzburg–Landau parameter 84. The upper critical field Hc2(T) shows an anomalous temperature dependence at low temperatures and the anisotropy of Hc2(T) is strongly T-dependent, both of which indicate a multiband scenario. The electronic specific heat (T) can be consistently described by a two-gap (s + d waves) model from the base temperature up to . Our results suggest nodal and multiband superconductivity in Ta4Pd3Te16.

Novel structural phases and superconductivity of iridium telluride under high pressures.

Transition metal selenide and telluride have recently receive considerable attention due to their possible structural relation to ferropnictide. Pressure is often used as an efficient way to modify the crystal or electronic structure that in many cases lead to new material states of interest. Here we search the structures of IrTe2 up to 150 GPa using crystal structure prediction techniques combining with ab initio calculations. Three new stable phases under high pressures are predicted, and their electronic structure properties, phonon spectra, and electron-phonon couplings are also investigated. Significant reconstructions of band structures and Fermi surfaces are found in these new phases. Calculated results show that while the C2/m-2 phase has bad metal behavior and very weak electron-phonon coupling, the and I4/mmm phases have relatively higher electron-phonon coupling up to ~ 1.5 and 0.7, respectively. The variable-composition searching have been performed, newly compounds with different stoichiometries, such as IrTe3, IrTe, and Ir3Te, are predicted to be thermodynamically and dynamically stable at high pressures. The pressure range investigated here is accessible in the diamond anvil cell experiments, thus our results might stimulate further experimental studies.

Highly efficient telluride electrocatalysts for use as Pt-free counter electrodes in dye-sensitized solar cells

Two transition metal tellurides, CoTe and NiTe2, were synthesized and for the first time employed as the counter electrodes (CEs) with high catalytic activity for reduction of I3(-) in dye-sensitized solar cells (DSCs). Using CoTe and NiTe2-based CEs, photoelectric conversion efficiencies (PCEs) of 6.92% and 7.21% were achieved for DSCs, respectively, comparable to that of 7.04% achieved when using a Pt-based CE. The results indicated that, serving as a CE in DSCs, telluride could be a cost-effective and efficient alternative to the noble metal Pt.

ChemInform Abstract: Neutrons Not Entitled to Retire at the Age of 60. More than Ever Needed to Reveal Magnetic Structures

AbstractReview: 25 refs.

Neutrons Not Entitled to Retire at the Age of 60: More than Ever Needed to Reveal Magnetic Structures

In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.

ChemInform Abstract: Reduced Ternary Rare‐Earth—Transition Metal Tellurides for the Smaller Rare‐Earth Elements. An Exploration and an Explanation of the Marked Stability Differentiation among the Rare‐Earth Elements in these Phases.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reduced Ternary Rare‐Earth–Transition Metal Tellurides for the Smaller Rare‐Earth Elements. An Exploration and an Explanation of the Marked Stability Differentiation among the Rare‐Earth Elements in These Phases

AbstractThe existence of further metal‐rich condensed cluster compounds in R–Z–Te systems has been synthetically explored for R = Sc, Y, Pr, Dy, Er, Tm, Yb, Lu and, mainly, Z = Ru, Rh, Pd, Ag, Ir, Pt, Au. Ten new examples of orthorhombic Er7Ni2Te2‐type (Imm2) have been identified and that for Dy7Ir2Te2 has been refined. Seven new examples of other ternary structure types plus X‐ray powder pattern evidence for 14 unknown phases have also been identified. To date the family of ternary R–Z–Te phases appears to be limited to those for R = Sc, Y, and Dy–Lu, a trend that is parallel to but more emphatic than those variations found among parallel cluster halide systems. Stability trends among the halide and especially the telluride series follow the I1 + I2 sums for the R elements well, the larger values of which are considered to reflect better mixing of R and Z valence d orbitals in the more stable phases.

Growth and Microstructural Characterization of Single Crystalline Nb3Te4 Nanowires

Novel Nb3Te4 nanowires have been successfully synthesized through the direct reaction and annealing of the elemental powders, by means of a vapor transport mechanism. This is the first instance of the production of group 5 transition metal telluride nanowires. Synthesis involved the initial formation of NbTe2 crystallites which were subsequently annealed to generate crystalline Nb3Te4 nanowires. Characterization using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS) confirmed the wires to be single crystalline, with their longitudinal axes coincident with the crystallographic c-direction of Nb3Te4. The nanowires ranged in dimension from 50 nm to ∼1 μm in diameter and from 1 to 30 μm in length.

Thermoelectric properties and antiferromagnetism of the new ternary transition metal telluride CrAuTe 4

The new ternary transition metal telluride CrAuTe 4 has been discovered through solid-state reaction of the elements. The crystal structure is solved in the monoclinic space group P2/ m (No. 10) with lattice parameters a=5.4774(7) A ̊ , b=4.0169(6) A ̊ , c=7.3692(13) A ̊ , and β=90.604(10)°. The structure is related to that of the binary compound AuTe 2, and a derivation of the structure of CrAuTe 4 from AuTe 2 is shown. Measurements of the thermopower, thermal conductivity, electrical resistivity, and magnetic susceptibility are presented. The compound undergoes a paramagnetic to antiferromagnetic transition at 255 K .

Crystal structure, electrical properties and electronic band structure of tantalum ditelluride

Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of . Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of -bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements.

Transition metal silicides and tellurides: Crystal structure, heat capacities, and derived thermodynamic properties from absolute zero to 2200 K

Abstract

Electrocatalytic properties of mixed transition metal tellurides (Chevrel-phases) for oxygen reduction

Pseudobinary molybdenum cluster tellurides (Chevrel phases) with mixed transition metal clusters of the type M x Mo6−xTe8 (M = Pt, Os, Ru, Rh) and the binary phase Mo6Te8 have been synthesized, structurally characterized and electrochemically investigated with respect to their electrocatalytic properties for oxygen reduction. A correlation of the number of electrons per cluster unit (NEC) with the open circuit potential (o.c.p.) in saturated oxygen electrolyte was found. The limitation of the o.c.p. values are due to the mixed potential developed with each electrode material due to molybdenum oxidation. The lowest corrosion tendency and highest catalytic activity are found in the telluride phases when NEC (in the valence band) approaches 24.

Transition metal chalcogenides: new views on an old topic

In this contribution we discuss a group of layered tellurides with modular structures (tinker toy phases) and possible low temperature routes for the synthesis of chalcogenides with porous structures. Layer compounds of general composition [(M2Te2)(ATe2)](MTe2)n and related phases have been synthesized as main group counterparts of layered metal-rich early transition metal tellurides. Special features of these compounds are (i) the unusual square planar Te coordination of the main group atoms Ga, Si, and Ge and (ii) their modular structure based on four building blocks. Similarly to layered metal-rich early transition metal tellurides these phases are electronically stabilized by extensive bonding between early transition metals and main group “heteroatoms”. Size effects are important for the structural stability of the tinker toy phases; attempts to substitute A = Ga by the group homologues B or In lead to the formation of alternate phases such as Ta4BTe8 containing metal clusters with interstitial atoms or intercalate phases such as InxNb3Te4. Reactions in thiophosphate fluxes and under solvothermal conditions have been explored in order to synthesize materials with microporous structures. The formation of (poly)thiophosphates such as K2MP2S7 (M = V, Cr) and K4Ti2P6S25 shows that reactions in molten thiophosphates are controlled by the redox equilibria and the basicity of the flux. The reaction conditions prevent the use of templates which are needed for the formation of compounds with porous structures. Reaction of telluroarsenates with Cr(CO)6 under solvothermal condition, however, results in the formation of a unique polytelluride [Cr(en)3][Te6] with a microporous structure. Solvated Cr(en)33+ cations serve as templates in the synthesis of this material.

Electron correlations in transition metal-telluride cluster compounds

Abstract We report the magnetic properties of a new class of materials: Ni9Te6n+ with n = 0, 1, 2. These cluster compounds, which can be charged by chemical means from neutral to 2 +, provide a unique and novel way to change the Fermi level. For most charge states, we observe quenching of the spin and orbital moments at low temperatures, accompanied by a large value for the temperature-independent susceptibility of the ground state. The magnitude and universality of these results among different charge states can be explained neither by local moments in a finite size system nor by the molecular orbital approximation. The generic presence of low-energy magnetic excitations in these compounds indicates that these systems exhibit strong electron correlations and form mesoscopic analogues of the mixed valence/heavy fermion compounds.

Thermochemistry of transition metal tellurides of interest in nuclear technology

The binary systems of tellurium with the alloying constituents of stainless steel, viz. Fe, Cr, Ni, Mo and Mn, were investigated by using high temperature mass spectrometry. The partial pressures of Te 2 and Te, which were the only species detected in the vapour phase in all the cases except MnTe, were obtained as a function of temperature and composition. All the telluride phases were found to be nonstoichiometric and their homogeneity ranges broader than hitherto recognised. Thermodynamic parameters such as enthalpy of vaporisation, enthalpy of formation and Gibbs free energy of formation were deduced for various compositions. The threshold tellurium potential necessary for the corrosion of the clad was calculated for each alloying constituent, and this data was compared with the estimated tellurium potential in the fuel-clad gap of the fuel pins in fast breeder reactors. The role of fission product tellurium in the internal corrosion of the clad is discussed in the light of the above data.