Use Of Tellurium Research Articles

Evaluation of Efficiency for Miniscale Thermoelectric Converter under the Influence of Electrical and Thermal Resistance of Contacts

Mass-produced thermoelectric modules are mainly fabricated with Bi2Te3-based materials. Due to the limited world reserves and the high price of tellurium, it must be saved. The miniaturization of thermoelectric converters is one of the modern trends to diminish the use of tellurium, reduce the cost of modules and expand the range of their applications. The main disadvantage of miniature thermoelectric converters operating in cooling or generating modes is their low energy efficiency, caused by the effect of electrical and thermal resistances of contacts, interconnectors and insulating plates. We propose an improved method for evaluating the maximum efficiency that takes into consideration the impact of these unwanted resistances. This method can also be used to design the modules with the optimal structure for cooling and energy generation, and not only to study their performance. The effect of undesirable electrical and thermal resistances on the maximum efficiency of cooling and generating converters made of Bi2Te3-based materials is analyzed. It is shown that the efficiency of miniature modules can be significantly improved if these resistances are reduced to their rational values. The decrease in electrical contact resistance is the predominant factor. The rational values to which it is advisable to decrease the electrical contact resistance have been determined. In the development of miniscale module technology, it is necessary to focus on such rational contact resistance values.

Tolerance, Adaptation, and Cell Response Elicited by Micromonospora sp. Facing Tellurite Toxicity: A Biological and Physical-Chemical Characterization.

The intense use of tellurium (Te) in industrial applications, along with the improper disposal of Te-derivatives, is causing their accumulation in the environment, where oxyanion tellurite (TeO32−) is the most soluble, bioavailable, and toxic Te-species. On the other hand, tellurium is a rare metalloid element whose natural supply will end shortly with possible economic and technological effects. Thus, Te-containing waste represents the source from which Te should be recycled and recovered. Among the explored strategies, the microbial TeO32− biotransformation into less toxic Te-species is the most appropriate concerning the circular economy. Actinomycetes are ideal candidates in environmental biotechnology. However, their exploration in TeO32− biotransformation is scarce due to limited knowledge regarding oxyanion microbial processing. Here, this gap was filled by investigating the cell tolerance, adaptation, and response to TeO32− of a Micromonospora strain isolated from a metal(loid)-rich environment. To this aim, an integrated biological, physical-chemical, and statistical approach combining physiological and biochemical assays with confocal or scanning electron (SEM) microscopy and Fourier-transform infrared spectroscopy in attenuated total reflectance mode (ATR-FTIR) was designed. Micromonospora cells exposed to TeO32− under different physiological states revealed a series of striking cell responses, such as cell morphology changes, extracellular polymeric substance production, cell membrane damages and modifications, oxidative stress burst, protein aggregation and phosphorylation, and superoxide dismutase induction. These results highlight this Micromonospora strain as an asset for biotechnological purposes.

Tellurium spectrometer for 1S0-1P1 transitions in strontium and other alkaline-earth atoms.

We measure the spectrum of tellurium-130 in the vicinity of the 461nm S01-P11 cycling transition in neutral strontium, a popular element for atomic clocks, quantum information, and quantum-degenerate gases. The lack of hyperfine structure in tellurium results in a spectral density of transitions nearly 50 times lower than that available in iodine, making use of tellurium as a laser-frequency reference challenging. By frequency-offset locking two lasers, we generate the large frequency shifts required to span the difference between a tellurium line and the S01-P11 resonance in strontium or other alkaline-earth atoms. The resulting laser architecture is long-term frequency stable, widely tunable, and optimizes the available laser power. The versatility of the system is demonstrated by using it to quickly switch between any strontium isotope in a magneto-optical trap and by adapting it to spectroscopy on a thermal beam with a different alkaline-earth atom.

Unraveling H+/Zn2+ Sequential Conversion Reactions in Tellurium Cathodes for Rechargeable Aqueous Zinc Batteries.

Progress toward practical rechargeable aqueous zinc (Zn) batteries is impeded by the low energy density. The use of tellurium (Te) cathodes featuring multielectron redox reactions offers one possible approach to mitigating this dilemma. However, the corresponding energy-storage mechanisms in aqueous electrolytes are not established yet. Here, we uncover a H+/Zn2+-involved sequential conversion reaction with 6e- transfer for Te-based cathodes, which accounts for the outstanding capacity (over 460 mAh g-1 at 50 mA g-1). Two distinct redox processes, corresponding to TeO2 ↔ Te and Te ↔ ZnTe, are explicitly revealed within the electrochemical window of routine aqueous Zn electrolytes. The mechanism elucidated here complements the understanding of energy-dense Te centers and propels the exploration of high-capacity electrodes for multivalent battery chemistries.

Anisotropic thermoelectric transport in textured Sb1.5Bi0.5Te3 nanomaterial synthesized by facile bottom-up physical process

High anisotropy in thermal conductivity (κ) coupled with anisotropy in Seebeck coefficient (S) has resulted in peak zT value of 0.85 at 150 °C in the textured Sb1.5Bi0.5Te3 nanomaterial in perpendicular to the preferential ab-plane direction. Further, strong and opposite temperature dependences in electrical conductivity (σ) and thermal conductivity, in the ranges of 1.6–1.8 and 1.4–1.8 respectively, have resulted in better average zT value of 0.72 in the 50°C–250 °C temperature range along this direction, where zT = (S2σ/κ)T. The high anisotropy in Seebeck coefficient in the range of 0.82–0.84 is peculiar, which may be attributed to differential scattering for holes and electrons by oxide interface on the ab-planes. Sample temperature and laser power dependent Raman spectroscopy have revealed that Eg(2) mode is dominant phonon transfer mode in this material and therefore, scattering of Eg(2) mode phonons may be critical in obtaining thermal conductivity reduction. The nanomaterial has been synthesized by a facile bottom-up physical synthesis process and consolidated by direct current hot pressing. Our synthesis process requires controlled melting of ingredient metals at just above their melting points-rocking and air quenching. The synthesized nanomaterial hardly experiences its melting point in this process. This energy efficient process does not require any kind of milling and produces single phase nanomaterial in unique plate-like morphology, which easily results in high texturing. This texturing has been studied by XRD analysis as well as SEM images and is also correlated with texture factor in the thermoelectric measurements. HRTEM image has shown high grain boundary density within the plates, but these have not been able to scatter phonons for thermal conductivity reduction within ab-plane. This is possibly due to smaller than optimum size of these randomly oriented grains. Such features also offer possibility of zT enhancement along preferential ab-plane direction in the textured specimen. Further, the study of anisotropy in power output density and thereby, engineered power factor under practical temperature gradients is also presented. The process also offers simplicity in obtaining further thermal conductivity reduction in perpendicular to the preferential ab-plane direction by use of tellurium or semiconductor interface layer or by use of metallic cluster in the ab-plane direction.

Lithium–Tellurium System: Thermodynamic and Electrochemical Studies and Prospects for Use in Chemical Current Sources

Published data on the lithium–tellurium phase diagram and on thermodynamic properties of liquid alloys and solid phases formed are summarized and comprehensively analyzed in connection with prospects for using tellurium and its compounds and composites in various energy conversion systems involving lithium. The results of studying the thermodynamic properties of lithium tellurides by different methods are compared. The results of the main studies dealing with the use of tellurium in chemical current sources (CCSs) of various designs are briefly considered.

Semiconducting Polymers Containing Tellurium: Perspectives Toward Obtaining High-Performance Materials

The development of high-carbon-content polymers for optoelectronics is an area of intense research; however, carbon-rich materials have certain limitations that arise from their composition. Some of these limitations can be overcome by the judicious incorporation of heavier elements which do not significantly change the carbon content to a point where it adversely affects cost and processability. Here we examine the use of tellurium as a heavy atom in the design of optoelectronic polymers. Group 16 atom (O, S, Se, Te) substitution is a promising strategy for the development of high performance materials for organic electronic applications. The use of tellurium in place of selenium or sulfur in conjugated polymers lends new properties to these materials such as red-shifted optical absorption, high polarizability, high dielectric constant, and strong intermolecular interactions. These properties are favorable for organic photovoltaics (OPVs) and organic field effect transistors (OFETs). In particular, extending the absorption range to the near-IR allows for more efficient solar harvesting since low-energy photons are most abundant. Additionally, strong Te–Te interactions lead to enhanced interchain electronic coupling, which is expected to facilitate charge transport. The use of polymers containing tellurophene, the tellurium analogue of the well-studied thiophene, has only recently begun to emerge in the literature. New synthetic routes have been developed, and there now exist a handful of tellurophene-containing polymers that have been synthesized and used to fabricate OPVs and OFETs. Their performance in OPVs has not surpassed that of their lighter chalcogen analogues; however, the use of tellurophene-containing materials is a young field, and continued efforts in the development of new materials and device optimization should lead to improved performance. In this Perspective we discuss the current status of tellurium-containing polymers in terms of their synthesis, properties, and performance. We highlight the challenges that have been overcome thus far and emphasize those that should be the focus of future work. This includes overcoming synthetic challenges and developing an understanding of the current limitations in device performance with tellurium-containing polymers through studies of materials properties and excited state dynamics. We also suggest new applications and directions for tellurium-containing materials beyond OPVs and OFETs.

Tellurium Compound AS101 Ameliorates Experimental Autoimmune Encephalomyelitis by VLA-4 Inhibition and Suppression of Monocyte and T Cell Infiltration into the CNS

Multiple sclerosis (MS) is an inflammatory autoimmune disease of the central nervous system (CNS) involving demyelinating and neurodegenerative processes. Several of the major pathological CNS alterations and behavioral deficits of MS are recapitulated in the experimental autoimmune encephalitis (EAE) mouse model in which the disease process is induced by administration of myelin peptides. Development of EAE requires infiltration of inflammatory cytokine-generating monocytes and macrophages, and auto-reactive T cells, into the CNS. Very late antigen-4 (VLA-4, α4β1) is an integrin molecule that plays a role in inflammatory responses by facilitating the migration of leukocytes across the blood-brain barrier during inflammatory disease, and antibodies against VLA-4 exhibit therapeutic efficacy in mouse and monkey MS models. Here, we report that the tellurium compound AS101 (ammonium trichloro (dioxoethylene-o,o') tellurate) ameliorates EAE by inhibiting monocyte and T cell infiltration into the CNS. CD49d is an alpha subunit of the VLA-4 (α4β1) integrin. During the peak stage of EAE, AS101 treatment effectively ameliorated the disease process by reducing the number of CD49d(+) inflammatory monocyte/macrophage cells in the spinal cord. AS101 treatment markedly reduced the pro-inflammatory cytokine levels, while increasing anti-inflammatory cytokine levels. In contrast, AS101 treatment did not affect the peripheral populations of CD11b(+) monocytes and macrophages. AS101 treatment reduced the infiltration of CD4(+) and CD49(+)/VLA4 T cells. In addition, treatment of T cells from MS patients with AS101 resulted in apoptosis, while such treatment did not affect T cells from healthy donors. These results suggest that AS101 reduces accumulation of leukocytes in the CNS by inhibiting the activity of the VLA-4 integrin and provide a rationale for the potential use of Tellurium IV compounds for the treatment of MS.

Analysis of tellurium as n-type dopant in GaInP: Doping, diffusion, memory effect and surfactant properties

The use of tellurium as n-type dopant for GaAs and InP has several advantages, including a high incorporation efficiency, the very high doping levels achievable and a low diffusion coefficient. However, its use to dope Ga x In 1− x P is not straightforward, since it shows several problems like a remarkable memory effect and an acute inertia of the material to become Te-doped, which gives rise to gradual doping profiles. In this paper, all these phenomena are studied and quantified using secondary ion mass spectroscopy (SIMS) and electrochemical CV profiling (ECV) measurements. Concerning the gradual doping profiles, their origin is linked to the interaction of Te and In in the gas phase and on the growth surface. A phenomenological explanation is given for this effect although the exact physical processes behind remain to be defined.

The influence of stoichiometry on the growth of tellurium-doped indium antimonide for magnetic field sensors

Indium antimonide magnetoresistors are used as magnetic position sensors in very demanding automotive environments such as crankshaft and camshaft sensors for engine control. The use of tellurium as an n-type dopant was studied using Hall effect measurements up to 200°C, Hall depth profiling, and secondary ion mass spectroscopy. The films were grown by metal organic chemical vapor deposition using trimethyl indium, trisdimethylamino antimony, and diethyl telluride. It was found that the incorporation of tellurium strongly depends upon the V/III ratio during growth, implying that it is influenced by the availability of antimony vacancies. Thus, our results show that the reproducibility of tellurium doping is not limited by memory effects in a well-designed reactor, but by the control of stoichiometry. It is now possible to grow films with optimum doping profile and with good uniformity and reproducibility over hundreds of growth runs. These films can be used to make magnetoresistors that have good sensitivity to a magnetic field and good stability over a wide temperature range.

INVESTIGATIONS OF HETEROCYLIC SYSTEMS CONTAINING NITROGEN-TELLURIUM BONDS

The syntheses of 2,1,3-benzotellaradiazole and 3,4-dimethylbenzo-2,1,3-telluradiazole were attempted by reacting tellurium dioxide with the relevant diamine. The structures of the synthesised tellurium compounds, however, were not as expected. The attempted synthesis of 2,1,3-benzotelluradiazole yielded, instead, its hydrated analogue; benzo-2-telluroxo-1,3-diazole (1). The high melting point and lack of solubility in all common solvents of (1) suggests that it may exist in a polymeric form in the solid state. The attempted synthesis of 3,4-dimethylbenzo-2,1,3-telluradiazole afforded, in small yield, an organic compound, 1 -amino-3,4,7,8-tetraethylphenazine (2), the crystal structure of which was elucidated. This compound is believed to have arisen from the removal of tellurium from the expected diazole, thus yielding a highly reactive intermediate. An attempt to trap this intermediate using dimethyl fumarate proved unsuccessful. The use of tellurium tetrachloride as the tellurium source, in place of tellurium dioxide, yielded 3,4-dimethylbenzo-2,2dichloro-2,1,3-telluradiazole.

Pseudomorphic high electron mobility heterostructures with extremely high conductivity using Te as n-type dopant by low-pressure metal organic chemical vapor deposition

Modulation-doped AlxGa1−xAs/InyGa1−yAs/GaAs single-quantum-well structures have been grown by low-pressure metal organic vapor phase epitaxy and characterized by Hall, C-V measurements, and photoluminescence spectroscopy. The use of tellurium instead of silicon as an n-type dopant for AlxGa1−xAs increases the electron concentration without decreasing the electron mobility. High free-electron concentrations of ns=7.5×1012 cm−2 (300 K) and ns=3.7×1012 cm−2 (77 K), and Hall mobilities of μ=5470 cm2 (V s)−1 (300 K) and μ=24 600 cm2 (V s)−1 (77 K) were obtained. The high concentration and mobility product of the channel: nsμ=4.1×1016 (V s)−1 at 300 K and nsμ=9.1×1016 (V s)−1 at 77 K, makes it a preferred choice for high-speed applications.

Use of tellurium(IV) and tellurium(VI) as oxidants in organic synthesis

Use of tellurium(IV) and tellurium(VI) as oxidants in organic synthesis