Te Ions Research Articles

Bi6Te2-xRxO13 (R=Ti, Si, Ce) Systems: A Investigation for Fuel Cell Applications

In recent years, the increase of economic and environmental problems related to energy generation has increased researches at renewable energy sources. Among others, the fuel cells excel as promising alternative technology of electricity generation and materials science is an ally in the search for better and more efficient materials for this application. In particular, solid-state ionic conductors represent functional materials with promising advantages for fuel cells, as is the case of Bi2O3-based oxygen ion conductors, however, they need to have its cubic phase stabilized at room temperature. This paper presents a study of the Bi6Te2-xRxO13 (R = Ti, Si and Ce) systems for such an application. Solid state reaction was used to materials synthesis. The 3Bi2O3:2TeO2 system present two phases, an orthorhombic one (Bi6Te2O15) stable at room temperature and another high temperature cubic (Bi6Te2O13). Experiments of substitution of Te ions by Ti, Si and Ce ions using the Bi6Te2- xRxO13 matrix were done intending to stabilize the cubic phase at room temperature and the results are presented as well as discussed here.

In situ, synthesis of chitosan fabricated tellurium nanoparticles for improved antimicrobial and anticancer applications

The emergence of antibiotic resistance has had a severe impact on human health and economic burdens, drawing attention to the development of novel antimicrobial therapies. Polymer-metal composites have shown evidence of therapeutic applications by exerting antimicrobial effects and delivering these antimicrobials with biocompatibility. Therefore, this study prepared and characterized chitosan (CS)-fabricated tellurium nanoparticles (Te NPs) for enhanced antimicrobial, antioxidant, and cytotoxicity applications. The CS-Te NPs were spherical, polydisperse, and distributed within the CS matrix with an average size of 37.48 ± 14.56 nm, as confirmed by TEM analysis. CS-Te NPs exhibited positive zeta potential in neutral (pH 7.0: 7.90 ± 1.86 mV) and acidic environment. XRD analysis confirmed the crystalline nature of CS-Te NPs, and these nanoparticles exhibited good thermal and less porosity. A higher release of Te ions occurred from CS-Te NPs at an acidic pH. Further, CS-Te NPs displayed stronger antibacterial and antibiofilm activity against E. coli and S. enterica. Furthermore, CS-Te NPs exhibited significant free radical scavenging activity against ABTS and DPPH free radicals. Moreover, these nanoparticles demonstrated cytotoxicity against cancerous cells (A549 and PC3 cells) when compared to normal cells (NIH3T3 cells). Therefore, this study suggests that CS-Te NPs could serve as a substantial therapeutic agent.

Alginic acid-functionalized silver nanoparticles: A rapid monitoring tool for detecting the technology-critical element tellurium

The increasing global demand for tellurium, driven by its critical role in alloys, photovoltaic devices, and electronics, has raised concerns about its environmental pollution and neurotoxicity. In response, the potential of alginic acid (AA), a renewable, low-cost, and sustainable biopolymer, was explored for the biosynthesis of ultra-small silver nanoparticles (AgNPs) and their application in the detection of tellurium (Te(IV)). The effect of key synthesis parameters on desired physicochemical properties and yield of AgNPs was established to ensure high specificity and sensitivity towards Te(IV). The purified AgNPs with AA surface ligands were utilized to demonstrate a ratiometric absorbance sensor that exhibits excellent linearity and nanomolar-level affinity. This approach achieved a high correlation coefficient of ∼ 0.982, with a low detection limit of about 22 nM. Further investigations into the effect of pH, ionic strength, and organic molecules were conducted to elucidate detection performance and molecular understanding. The detection mechanism relies on the coordination between Te(IV) ions and the carboxylate groups of AA, which initiates aggregation-induced plasmon coupling in adjacent AgNPs. The capability of this analytical method to monitor Te(IV) in real-world water samples features its rapidity, user-friendliness, and suitability for point-of-care monitoring, making it a promising alternative to more complex techniques.

Te doping effects on the ferromagnetic performance of the MnGe/Si quantum dots grown by ion beam sputtering deposition

Dilute magnetic MnGe quantum dots (QDs) have been a popular research topic due to their great potential application on spintronics and their natural compatibility with today's highly developed silicon-based complementary metal oxide semiconductor (CMOS) technology. However, the relatively low Curie temperature impedes their ability to maintain the ferromagnetic phase and creates difficulty for their practical application in spintronics at room temperature. Here, we report the first preparation of the Te-doped dilute-magnetic Mn0.064Ge0.895Te0.041/Si QDs by using the ion beam composite target sputtering technique. Growth temperature and deposition thickness dependent QDs density and magnetic properties were investigated systematically. The experimental results indicate that the QD density of Mn0.064Ge0.895Te0.041/Si sample increases first and then reduces with the deposited thickness, while the QDs' diameters increase monotonously from 10.18 ± 0.21–33.6 ± 0.34 nm. Curie temperature of 369 K observed in Mn0.064Ge0.895Te0.041 QDs is higher than that of 295 K observed in Mn0.061Ge0.939 counterparts grown at the same conditions. Correspondingly, the saturation and residual magnetization in the former are much higher than in the latter. The ferromagnetic enhancement can be attributed to that the nonpolar Mn0.064Ge0.936 QDs transform into Rashba polar Mn0.064Ge0.895Te0.041 QDs with the doping of Te ions, which obviously promotes the exchange coupling between holes and Mn atoms. Our work provides a practical approach for improving the ferromagnetism and Curie temperature of silicon-based diluted magnetic semiconductor QDs.

Defect diamond-like tellurides as infrared nonlinear optical materials with giant second-harmonic generation tensor

As promising candidate for mid- and far-infrared (MFIR) nonlinear optical (NLO) materials, diamond-like (DL) chalcogenides have been extensively studied because of their considerable advantages. Among them, tellurides attract our attention as their stronger electron polarization and wider transmittance range than those of sulfides and selenides. Herein, the insightful structural characteristics and NLO properties of defect DL MGa2Te4 (M = Zn, Cd) were studied for the first time at experimental and theoretical level. They crystallize in the non-centrosymmetric I-4 space group (No.82), with a three-dimensional structure consisting of highly oriented [MTe4] and [GaTe4] tetrahedra, which can be viewed as derived from AgGaS2 (AGS). Experimental results illustrate that MGa2Te4 (M = Zn, Cd) exhibits moderate band gaps, strong SHG intensities about 4.9–10.6 times that of AGSe at 90–125 μm, and congruent-melting behavior. Theoretical calculations based on E-field DFPT method indicate that the tremendous SHG tensors d14 of ZnGa2Te4 and CdGa2Te4 are 127.67 and 105.19 pm/V. SHG-density analysis reveals that the lone-pair packets of Te ions in [GaTe4] units are the main source of SHG responses. In addition, calculations on Mulliken bond order index imply that the main difference between these two crystals is the bonding modes of M−Te. Special care was also given to ensure convergence of k-mesh for both conventional and primitive cells of the crystals, with two different methods for calculating linear and non-linear optical properties compared side by side. This work demonstrates the potential applications of these two defect DL tellurides in the MFIR NLO field.

Active sites of Te-hyperdoped silicon by hard x-ray photoelectron spectroscopy

Multiple dopant configurations of Te impurities in close vicinity in silicon are investigated using photoelectron spectroscopy, photoelectron diffraction, and Bloch wave calculations. The samples are prepared by ion implantation followed by pulsed laser annealing. The dopant concentration is variable and high above the solubility limit of Te in silicon. The configurations in question are distinguished from isolated Te impurities by a strong chemical core level shift. While Te clusters are found to form only in very small concentrations, multi-Te configurations of type dimer or up to four Te ions surrounding a vacancy are clearly identified. For these configurations, a substitutional site location of Te is found to match the data best in all cases. For isolated Te ions, this matches the expectations. For multi-Te configurations, the results contribute to understanding the exceptional activation of free charge carriers in hyperdoping of chalcogens in silicon.

Gate and Temperature Driven Phase Transitions in Few-Layer MoTe2

MoTe2 has a stable hexagonal semiconducting phase (2H) as well as two semimetallic phases with monoclinic (1T') and orthorhombic (Td) structures. A structural change can thus be accompanied by a significant change in electronic transport properties. The two semimetallic phases are connected by a temperature driven transition and could exhibit topological properties. Here we make extensive Raman measurements as a function of layer thickness, temperature, and electrostatic doping on few layer 2H-MoTe2 and also on 1T'-MoTe2 and Td-WTe2. Recent work in MoTe2 has raised the possibility of a 2H-1T' transition through technology compatible pathways. It has been claimed that such a transition, of promise for device applications, is activated by electrostatic gating. We investigate this claim and find that few-layer tellurides are characterized by high mobility of Te ions, even in ambient conditions and especially through the variation of external parameters like electric field or temperature. These can generate Te clusters, vacancies at crystalline sites, and facilitate structural transitions. We however find that the purported 2H-1T' transition in MoTe2 cannot be obtained by a pure electrostatic field.

The performance evaluation of Alamine336 in solvent extraction and polymer inclusion membrane methods for valuable ions extraction: A case study of Te(IV) separation intensification

In this research, extraction of Te(IV) from chloride solution was studied using Alamine336 extractant. In the solvent extraction experiments, Response Surface Methodology was employed to evaluate the effect of operating parameters on the extraction and stripping of Te(IV). According to results, two models were proposed for Te(IV) extraction and stripping. The ANOVA study verified the ability of the presented models to predict the experimental results. under the optimum operating parameters (Alamine336 concentration of 0.03 mol L−1, feed solution acidity of 2.36 mol L−1, temperature of 25°C, initial Te(IV) concentration of 210 mg L−1 and stripping phase pH of 8.5), Te(IV) extraction and stripping efficiency were 99.05% and 79.32%, respectively.In the polymer inclusion membrane (PIM) experiments, maximum transport of Te(IV) ions (64.58%) was achieved for membrane containing 40 wt.% Alamine336, initial acid concentration of 4 mol L−1, and receiving phase pH of 8.5.Under the optimum conditions, the extraction of Te(IV) from anodic copper sludge leach solution was 62.16% and 55.56% using the SX and the PIM processes, respectively. However, the PIM method had a higher selectivity towards Te(IV) ions.

Atomic scale analysis of Zn2+ storage in robust tunnel frameworks.

Realizing rapid and reversible Zn2+ storage at the cathode is imperative for the advancement of aqueous Zn-ion batteries (ZIBs), which offer an excellent option for large-scale electrochemical energy storage. However, owing to limitations of the structural stability of previously investigated frameworks, the Zn2+ storage processes remain unclear, thus hindering progress towards the above goal. Herein, we present the novel application of MoVTe oxide with an M1 phase (MVT-M1) as a potential cathode material for ZIBs. MVT-M1 features broad and robust tunnels that facilitate reversible Zn2+ insertion/extraction during cycling, as well as rich redox centers (Mo, V, and Te) to aid in charge redistribution, resulting in good performances in ZIBs. The exceptional resilience of MVT-M1 to high-energy electron beams allows for direct observation of Zn2+ insertion/extraction at the atomic scale within the tunnels for the first time using high-angle annular dark field scanning transmission electron microscopy; the storage location of zinc ions within the cathode is accurately determined layer by layer from the surface to the bulk phase by employing time-of-flight secondary ion mass spectrometry. Additionally, solvent molecules (H2O and methanol) are also found inside the tunnels along with Zn2+. Due to the broader heptagonal tunnels and Te ions in the hexagonal tunnels, MVT-M1 exhibits good cycling stability, outperforming MoVTe oxide with the M2 phase (no heptagonal tunnels) and MoV oxide with the M1 phase (no Te). These findings hold significant importance in advancing our understanding of the Zn2+ storage mechanism and enable the design of novel materials specifically optimized for efficient Zn2+ storage.

Facile synthesis strategy for cesium tin halide perovskite crystals toward light emitting devices and anti-counterfeiting flexible fiber.

All-inorganic metal halide perovskites are widely studied because of their excellent photoelectric properties. However, due to the toxicity of CsPbX3 (X = Cl, Br, I) perovskites, it is difficult to apply them on a large scale. The lead-free nature and air stability make Cs2SnX6 (X = Cl, Br, I) perovskites possible candidates to replace CsPbX3 perovskites. Herein, we report the perovskite crystals (PCs) based on Te(IV)-doped Cs2SnCl6: Cs2Sn1-xTexCl6. Cs2Sn1-xTexCl6 PCs showed yellow emission under a 365 nm ultraviolet lamp. The photoluminescence quantum yield (PLQY) of Cs2Sn0.94Te0.06Cl6 PCs was 57.09%, which was proposed to be from the triplet Te(IV) ion 3P1 → 1S0 self-trapping excitons (STE) recombination. The perovskite crystals can be used to fabricate light-emitting diodes (LEDs). The fiber paper prepared from aramid chopped fibers (ACFs) and polyphenylene sulfide (PPS) fibers showed a bright yellow light under 365 nm ultraviolet light after being post-processed with Cs2Sn1-xTexCl6 PCs solution. The ACFs/PPS compound fiber paper modified with Cs2Sn1-xTexCl6 PCs maintained exceptional optical properties and could be stored in air for more than 4500 h. The fluorescence performance of the modified ACFs/PPS compound fiber paper could be applied to fluorescence anti-counterfeiting. The modification strategy and the applications in this work will provide a good choice for studying the optical performance of perovskites and broaden the application of ACFs/PPS compound fiber paper.

Evidence of exchange striction and charge disproportionation in the magnetoelectric material Ni3TeO6

The chiral magneto-electric compound Ni3TeO6 is investigated through temperature-dependent synchrotron-based powder x-ray diffraction and x-ray absorption spectroscopy between 15 to 300 K. Our work provides direct evidence for the exchange-striction in the material around the concomitant onset point of collinear antiferromagnetic and magneto-electric phases. The x-ray absorption near edge spectra and x-ray photoelectron spectra show that the sample consists of both Ni2+ and Ni3+ ions in the lattice. The ionic state of Ni is found to be quite robust, and it is largely independent of the preparation route. Additionally, the minority Te4+ state is found to coexist with the majority Te6+ state, which may arise from the charge disproportionation between Ni and Te ions (Ni2+ + Te6+ --> Ni3+ + Te4+). The observed mixed valency of Ni is also confirmed by the total paramagnetic moment per Ni atom in the system. This mixed valency in the metal ions and the exchange-striction may be attributed to the observed magneto-electric effect in the system.

Simultaneously improving Rashba-type and Zeeman effects in two-dimensional multiferroics

First-principles calculations are performed to investigate Rashba-type and Zeeman effects in two-dimensional three-atom-layer structures $X\mathrm{Te}$/MnTe/$X\mathrm{Te}$ ($XMX, X=\text{Sn}$, Ge). It is found that the Rashba-type and Zeeman effects that typically compete against each other rather cooperatively work together and are improved in $XMX$, as compared to $X\mathrm{Te}/X\mathrm{Te}/X\mathrm{Te}$ ($XXX$). This cooperation and improvement are highly required in Majorana qubits for topological quantum computing, Josephson junction of topological superconductivity, and other phenomena. The Rashba-type effect is improved because replacing $X\mathrm{Te}$ by MnTe leads to a reduction of the thickness of $XMX$ and increases the interaction between the surface state of the lowest conduction bands and its neighboring states. The improved Zeeman effect in the $XMX$ structure arises from s-d and p-d exchange interactions between Te and Mn ions. The present strategy of simultaneously largely improving Rashba-type and Zeeman effects therefore provides a route to realize stable Majorana fermions, topological superconductivity, and other phenomena that require both large Rashba-type and Zeeman effects.

Te doping effect on the structure and ionic conductivity of LiTa2PO8 solid electrolyte

LiTa2PO8 (LTPO) is a new solid-state electrolyte material, which has high bulk ionic conductivity and low grain boundary ion conductivity. However, the conductivity of materials synthesized by conventional methods is much lower than the theoretically calculated values. In this work, large radius Te ion are doped at Ta (3)-site in order to enlarge the lattice parameters and increase Li content, which are beneficial for increasing ionic conductivity. The Te substitution changes the Ta surrounding environment, increases the binding capacity of Ta–O, and reduces the attraction of oxygen to lithium ions in the system. The prepared dense Li1.04Ta1.96Te0.04PO8 ceramic electrolyte exhibits a low activation energy of 0.193 eV and four times higher ion conductivity (4.5 × 10−4 S cm−1) than undoped samples. Moreover, Li1.04Ta1.96Te0.04PO8 shows a stable cycling performance in the symmetric Li/Li cells and the Li/CPE/Li1.04Ta1.96Te0.04PO8/LiFePO4 batteries with the separation of a thin PEO membrane.

Epitaxial Orientation Angle Tuned Disk-on-Rod Nanoheterostructures for Boosting Charge Transfer.

Controlling the compositions of Se(VI) and Te(VI) ions in a 2D disk on 1D structures of Sb(V) chalcogenides, disk-on-rod heterostructures having three different epitaxial angles with different surface facets are reported. Te injection temperature determined the composition, ensuring heterostructure formation with trigonal Sb2SexTe3-x disks on orthorhombic Sb2Se3 rods having orientation angles 180°, 135°, and 90°. The growth kinetics of disks connected at one/two heads of parent rods is manipulated using an Se precursor as a limiting reagent. Theoretical calculations established the energy minimization of different orientations, their possible formation, and suitability in energy transfer applications. Electrochemical measurements were also in agreement with theoretical calculations. Hence, this is a case study of advanced modular synthesis of disk-on-rod nanostructures, leading a step further in nanocrystal engineering for more desirable complex structures and their charge transfer property.

Quantitation of Estradiol and Testosterone in Serum Using LC-MS/MS.

Adult and pediatric endocrinology and oncology often requires measuring serum estrogens and testosterone at very low concentrations. Conventional immunoassay methods often lack the required performance to meet this analytical need, and mass spectrometry techniques must be employed. Our aim was to develop a sensitive HPLC-MS/MS assay for both estradiol (E2) and testosterone (Te) in serum, utilizing commercially available calibrators and without the need for chemical derivatization. Serum samples, after the addition of an internal standard, are combined with a hexane:ethyl acetate extraction solution. The samples are vortexed, and the organic layer is decanted into a clean sample tube and evaporated to dryness under a stream of nitrogen. The samples are reconstituted in a water:methanol solution and separated chromatographically using a reversed-phase HPLC column. Subsequent mass spectrometry is performed using both positive ion mode for Te and negative ion mode for E2.

ТЕСТ-РОССЫПИ НА ОСНОВЕ МОДИФИЦИРОВАННОЙ КОСТРЫ КОНОПЛИ ДЛЯ ЭКСПРЕССНОГО ОПРЕДЕЛЕНИЯ ПОДВИЖНЫХ ФОРМ ФОСФОРА И СУЛЬФИТОВ В ПОЧВАХ И ВОДНЫХ ПРОБАХ

The methods of manufacturing test placers and compositions for visual-blister colorimetric determination of concentrations of phosphate ions and sulfi te ions for their quantitative determination in soils and water bodies have been optimized. The test placer contains all the reagents for the analytical reaction. Placers allow the quantitative determination of phosphates and sulfi des in aqueous samples without prior preparation of reagent solutions. In a blister cell with a diameter of 6 mm, a much more intense color was achieved with a solution layer of no more than 2 mm. The application of reagents to the surface of homogenized and discolored hemp awns avoids their contact until the chemical analytical reaction takes place. The composition of placers and the conditions for applying reagents are optimized. Suffi ciently high acidity can be provided by hydrosulfate ions with the addition of a few drops of solution. The reaction proceeds in the volume of the added test solution, which is 2-3 drops.

Role of electronegativity to induce magnetism in ZnX1−x Y x (X = S/Se/Te and Y = Li/Be/B) chalcogenides

Ab-initio calculations were performed to investigate the structural, electronic, and magnetic characteristics of the selected first row (Y = Li, Be, and B) doped zinc-blende ZnX (X = S, Se, and Te) chalcogenides. Firstly, the structural stability of the doped materials is analyzed by computing the formation energies, which substantially depends on the dopant atomic numbers and Y-doped ZnSe systems are energetically more stable. It is established that when the electronegativity of the dopant is less than that of the host atom, magnetism is induced. Our results revealed that selected intrinsically non-magnetic dopants (Y = Li, Be, and B) induce magnetic characteristics in all the studied ZnX chalcogenides structures except the B-doped ZnTe system due to a very small electronegativity difference between B and Te ions. The most striking feature of the present study is that Be-doped ZnX materials display the half-metallic ferromagnetism, and Be 2p non-degenerate orbitals are playing a major role in inducing magnetism and metallicity. Hence, the present work proposed that doping engineering with suitable impurity elements having electronegativity larger than that of the host atom could be an effective way to tune the physical properties of chalcogenides for their technological potential applications in advanced-spin-based devices.

Enhancement of the spin-glass transition temperature through pd -orbital hybridization in Zn1−xMnxTe

To gain insight into the spin-glass state of diluted magnetic semiconductors, we have examined the magnetic and electronic properties of ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ using density-functional theory as well as performed magnetization measurements on the $x=0.43$ and 0.55 systems to demonstrate a clear spin-glass transition consistent with previous literature. Using a generalized gradient approximation, we investigate the electronic and magnetic properties for $x=0$, 0.075, 0.15, 0.25, and 0.50 doping levels using the magnetic moment of ${\mathrm{Mn}}^{2+}$ as guide for the dependence of the Hubbard onsite potential on the electronic structure. Simulations on both ferromagnetic (FM) and antiferromagnetic (AFM) configurations yield a distinct AFM ground-state preference, which is consistent with a zero-magnetic-moment spin-glass state. Here an onsite potential of up to 8 eV on the Mn $3d$ orbitals is needed to harden the magnetic moment toward $S=5/2$. From our analysis of the electronic structure evolution with doping and onsite potential, we confirm the semiconducting state of the Mn-doped ZnTe as well as show that the presence of Mn incorporated into the ZnTe matrix at the Zn lattice site produces magnetic interactions through the Te ions with a distinct Te-Mn $pd$-orbital hybridization. Furthermore, we show that this hybridization is activated with the Mn doping above 0.25 concentration, which corresponds to the doping level in which the spin-glass transition begins to rise. Therefore, it is likely that the coupling of $pd$-orbital hybridization of the Mn and Te $p$ orbitals is a precursor to the enhancement of the spin-glass transition temperature.

Fabrication of defect-rich bifunctional hollow NiTe2 nanotubes for high performance hydrogen evolution electrocatalysts and supercapacitors

Design and fabrication of bifunctional nanomaterials for energy conversion and storage systems have been receiving great attention. In this report, hollow NiTe2 nanotubes were efficiently synthesized utilizing a hydrothermal reaction route, and were subsequently employed as bifunctional materials for hydrogen evolution reaction (HER) and supercapacitors (SCs). The unique hollow structure can't only supply large surface area and abundant ions transport channels, but also shorten the ions transfer pathways between electrode and electrolyte. Furthermore, the rich defects and Te ions also improve the electrochemical performances to some extent. The electrochemical measurement results show the superior electrocatalytic activity of hollow NiTe2 nanotubes for HER (85 mV under 10 mA cm−2) and electrochemical capacitance for SCs (566 F g−1 @ 1.5 A g−1). Additionally, the hollow NiTe2 nanotubes-based electrodes present excellent electrochemical stabilities in HER and SCs, respectively. Our findings demonstrate that the hollow NiTe2 nanotubes should be good candidates as bifunctional materials for HER and SCs.

MXenes@Te as a composite material for high-performance aluminum batteries

The emerging two-dimensional (2D) materials, MXenes, play an important role in various fields of energy storage and exhibit excellent electrochemical performance. Herein, we prepared few-layered MXenes (F-Ti3C2Tx) and loaded Te on the surface of F-Ti3C2Tx by using a simple high-temperature evaporation method. In addition, the electrochemical performance of the aluminum battery with F-Ti3C2Tx as support material was studied. The initial charge/discharge specific capacities are 987/1096 mA h g−1 at 0.2 A g−1. An obvious discharge voltage plateau of about 1.3 V appears at various current densities. The specific capacity is about 258 mA h g−1 with MXenes@Te as the active material in the aluminum battery, which benefits from the excellent electronic conductivity of the MXenes and their 2D layered structure. Density functional theory calculations were carried out to explore the mechanism. Ti3C2O2@Te is more inclined to adsorb [AlCl4]− than Ti3C2O2. Furthermore, the valence change behavior of element Te was studied by using thermodynamic calculation (FactSage 7.1). X-ray photoelectron spectroscopy results show that when the battery is fully charged to 2.4 V element Te and Ti ions (Ti3+, Ti2+) are oxidized to Te4+ and Ti4+. In contrast to the charging process, the high-valence Te4+ and Ti4+ are reduced again during discharging. Element Te is reduced to lower-valence Te2− when the discharge voltage is lower than 0.6 V, and a higher charge voltage (2.56 V) is required for Te to be oxidized to Te6+.