Tellurium Oxide Research Articles

Structural Analysis, Characterization, and First-Principles Calculations of Bismuth Tellurium Oxides, Bi6Te2O15

A single crystal of Bi6Te2O15 was obtained from the melt of the solid-state reaction of Bi2O3 and TeO3. Bi6Te2O15 crystallizes in the Pnma space group (No. 62) and exhibits a three-dimensional network structure with a =10.5831(12) Å, b = 22.694(3) Å, c = 5.3843(6) Å, α = β = γ = 90°, V = 1293.2(3) Å3, and Z = 4. The structure was determined using single-crystal X-ray diffraction. An asymmetric unit in the unit cell, Bi3Te1O7.5, uniquely composed of four Bi3+ sites, one Te6+ site, and nine O2− sites, was solved and refined. As a bulk phase, Bi6Te2O15 was also synthesized and characterized using powder X-ray diffraction (XRD), infrared (FT-IR) spectrometry, and the thermogravimetric analysis (TGA) method. Through bond valence sum (BVS) calculations from the single crystal structure, Bi and Te cations have +3 and +6 oxidation numbers, respectively. Each Bi3+ cation forms a square pyramidal structure with five O2− anions, and a single Te6+ cation forms a six-coordinated octahedral structure with O2− anions. Since the lone-pair electron (Lp) of the square pyramidal structure, [BiO5]7−, where the Bi+ cation occupies the center of the square base plane, exists in the opposite direction of the square plane, the asymmetric environments of all four Bi3+ cations were analyzed and explored by determining the local dipole moments. In addition, to determine the extent of bond strain and distortion in the unit cell, which is attributed to the asymmetric environments of the Bi3+ and Te6+ cations in Bi6Te2O15, bond strain index (BSI) and global instability index (GII) were also calculated. We also investigated the structural, electronic, and optical properties of the structure of Bi6Te2O15 using the full potential linear augmented plane wave (FP-LAPW) method and the density functional theory (DFT) with WIEN2k code. In order to study the ground state properties of Bi6Te2O15, the theoretical total energies were calculated as a function of reduced volumes and then fitted with the Birch–Murnaghan equation of state (EOS). The band gap energy within the modified Becke–Johnson potential with Tran–Blaha parameterization (TB-mBJ) revealed a value of 3.36 eV, which was higher than the experimental value of 3.29 eV. To explore the optical properties of Bi6Te2O15, the real and imaginary parts of the dielectric function, refraction index, optical absorption coefficient, reflectivity, the real part of the optical conductivity extinction function, and the energy loss function were also calculated.

Epitaxial Stabilization of Perovskite ATeO3 Thin Films

Tellurium oxides of the ATeO3 form typically do not crystallize in perovskite structures. Here, we show that perovskite-like ATeO3 (A = Ca, Sr, Ba) thin films can be grown on perovskite single-crystal substrates via epitaxial stabilization. These films are stable with high optical bandgaps, low dielectric losses, and a high electric breakdown strength. Hysteretic dielectric behavior found in SrTeO3 and BaTeO3 strongly suggests the presence of antiferroelectricity and ferroelectricity, respectively. These properties make perovskite tellurium oxides possibly appealing candidates for thin film coating or insulator materials in advanced microelectronics. Tellurium oxides constitute a largely unexplored class of materials that might show new and interesting functionalities in epitaxial thin-films. Our work encourages new work within this field.

Femtosecond laser-induced glass refractive index change in tellurite glass

Tellurite glass has excellent infrared optical properties and is widely used in lasers, optical communications, and sensing. Femtosecond laser direct writing is a preferred method for manufacturing tellurite photonic devices, which requires precise control of the variable of refractive index. However, accurate testing of the refractive index changes induced by femtosecond laser in tellurite glass is challenging due to the small magnitude of change and localized region. In this study, we present a novel approach to measure the refractive index change of tellurite glass through the utilization of volume phase grating (VPG) diffraction. We first investigated the laser-induced damage threshold (LIDT) of tellurite glass and then proceeded to prepare VPGs inside the glass by using femtosecond laser direct writing technology, ensuring that the laser energy remained below the LIDT. By measuring the thickness and diffraction efficiency of VPGs prepared under different laser energies, we determined the associated change in refractive index. In our experiment, when subjected to laser incidence with wavelengths of 632.8 and 808 nm, the maximum values of refractive index change in the laser-modified region are measured to be 1.97 × 10−3 and 1.61 × 10−3, respectively. This method offers a precise means of measuring refractive index change within the microregion of tellurite glass induced by femtosecond laser. This capability holds great significance for the fabrication of high-quality tellurite glass photonic devices using lithography-based techniques.

Evidence of Chlorotellurate(IV) – Hydroxochlorotellurate(IV) species equilibrium upon dissolution of tellurite glasses in aqueous hydrochloric acid: A Raman spectroscopic study

Raman spectroscopy has been used to elucidate the structure of tellurium (IV) oxide and its binary mixtures with thallium oxide both in the glassy state and in aqueous hydrochloric acid solutions. The addition of Tl2O in pure TeO2 glass results in the progressive transformation of TeO4 trigonal bipyramid (tbp) to TeO3 trigonal pyramid (tp) units in agreement with the literature findings. Thallium oxide acting as a modifier for the tellurite network, reduces the functionality of the initial unit and lowers the continuous network rigidity. The spectral changes upon dissolution of the 0.2Tl2O-0.8TeO2 glass in aqueous hydrochloric acid solution have also been measured revealing that the main structural units of the glass structure did not survive in a solution state and the connectivity of the glass network has completely collapsed. The systematics and the concentration dependence of the spectra acquired from different solutions indicate the presence of several chlorotellurate(IV) and hydroxochlorotellurate(IV) ionic species. The spectroscopic data are interpreted in such a way in order to indicate a dynamic equilibrium between the TeCl62− anion and the TeCl4(OH)− species. A combined analysis of the polarized and depolarized scattered intensity is presented here which aimed at elucidating the presence of additional species including the TeCl4(OH)22− and TeCl3(OH) species, respectively. The proposed model is discussed in the framework of the current phenomenological status of the field.

Passivation effect on Cd0.95Mn0.05Te0.98Se0.02 radiation detection performance

CdTe-based detectors have the problem of Te-rich surface layers caused by Br etching, which is one of fabrication steps. Te-rich layer acts as a trapping center and serves as an additional source of charge carriers, thereby degrading transport property of charge carriers and enriching leakage current on surface of detector. To solve this problem, we introduced sodium hypochlorite (NaOCl) as a passivant, and investigated its effect on Cd0.95Mn0.05Te0.98Se0.02 (CMTS), by analyzing chemical state of surface and its performance. After passivation with NaOCl, the results of X-ray photoelectron spectroscopy (XPS) shows the formation of tellurium oxide and elimination of water on CMTS surface, and CMTS presented enhanced performance with Am-241 radioisotope. Consequently, it is demonstrated that the passivation with NaOCl reduces leakage current, compensates defect, and elevates transport of charge carriers, thereby decreasing charge loss of carriers and improving performance of CMTS detector.

AAl(Te4O10) (A = Na, Ag) and K2Ga2(HTe6O16)(HTeO3): Three Aluminum/Gallium Tellurites with Large Birefringence and Wide Band Gap

The exploration of novel inorganic tellurites is significant because of their promising applications in nonlinear-optical materials and birefringent materials. Herein, three new aluminum/gallium tellurites, namely, NaAl(Te4O10) (1), AgAl(Te4O10) (2), and K2Ga2(HTe6O16)(HTeO3) (3), have been successfully obtained by mild hydrothermal reactions. The isostructural compounds 1 and 2 contain the Te3O8 trimer, while compound 3 contains an unprecedented Te6O16 hexamer. Notably, all three compounds exhibit large birefringence values of over 0.1 at 532 nm, which are currently the largest reported birefringence values among tellurium(IV) oxides without additional anionic groups.

Elucidating the structure-nonlinear optical property relationship of Te2O4(OH)2

A mixed-valent tellurium oxide hydroxide, Te2O4(OH)2, containing both tetravalent (IV) and hexavalent (VI) tellurium cations has been synthesized using a hydrothermal reaction method. Single crystal X-ray diffraction reveals that the compound crystallizes in the polar noncentrosymmetric space group, Pna21 (no. 33). The reported compound has a layered structure consisting of Te(VI)O4(OH)2 octahedra and Te(IV)O4 seesaw, in which each layer is aligned through interlayer hydrogen bonds. In addition to the structural refinements, the structure and optical properties of the material have been studied and compared with Te2O5, which is dehydrated residue of the title compound. Second harmonic generation (SHG) measurements indicate that the Te2O4(OH)2 exhibits a large SHG efficiency of ca. 4.7 times that of KH2PO4. The ultraviolet–visible diffuse reflectance spectrum shows that the material has a band gap of ca. 3.5 eV, corresponding to a UV cutoff edge of 354 nm. These values suggest that the compound has expanded its band gap while maintaining its SHG response, compared to Te2O5. Theoretical calculations using the density functional theory have been also performed to clarify the structure-property relationship of the reported material more effectively.

Iron nanoparticles embedded in polypyrrole and tellurium oxide ternary nanocomposites for electrical conductivity and electromagnetic interference shielding

Iron nanoparticles embedded in polypyrrole and tellurium oxide ternary nanocomposites for electrical conductivity and electromagnetic interference shielding

Formation and Transformation of Cu2-xSe1-yTey Nanoparticles Synthesized by Tellurium Anion Exchange of Copper Selenide.

Ion exchange reactions of colloidal nanoparticles post-synthetically modify the composition while maintaining the morphology and crystal structure and therefore are important for tuning properties and producing otherwise inaccessible and/or metastable materials. Reactions involving anion exchange of metal chalcogenides are particularly interesting, as they involve the replacement of the sublattice that defines the structure while also requiring high temperatures that can be disruptive. Here, we show that the tellurium anion exchange of weissite Cu2-xSe nanoparticles using a trioctylphosphine-tellurium complex (TOP═Te) yields weissite Cu2-xSe1-yTey solid solutions, rather than complete exchange to weissite Cu2-xTe, with compositions that are tunable based on the amount of TOP═Te used. Upon storage at room temperature in either solvent or air, tellurium-rich Cu2-xSe1-yTey solid solution nanoparticles transform, over the span of several days, to a selenium-rich Cu2-xSe1-yTey composition. The tellurium that is expelled from the solid solution during this process migrates to the surface and forms a tellurium oxide shell, which correlates with the onset of particle agglomeration due to the change in surface chemistry. Collectively, this study demonstrates tunable composition during tellurium anion exchange of copper selenide nanoparticles along with unusual post-exchange reactivity that transforms the composition, surface chemistry, and colloidal dispersibility due to the apparent metastable nature of the solid solution product.

TeO2–ZnO (tellurium oxide – Zinc oxide) thin film deposition by the thermionic vacuum arc plasma

In this study, 75TeO2–25ZnO and 70TeO2–30ZnO (mol %) (TZ) glasses were synthesized by using a traditional melt-quenching method. The synthesized TZ glasses were deposited as a thin film using the thermionic vacuum arc (TVA) system. The structure of the deposited TZ thin films and the synthesized TZ bulk glass samples were compared. The structural properties of the TZ thin films and bulk glass samples were determined by using X-ray diffraction (XRD) analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy (FT-IR). The morphological properties of the TZ thin films were obtained by using field emission scanning electron microscopy (FE-SEM) images and atomic force microscopy (AFM). The optical properties of bulk glass samples are obtained with ultraviolet–visible spectrophotometry in the range of 350–1000 nm. Lastly, the electrical properties were obtained by using dielectric spectroscopy. XRD and Raman analysis showed that the TZ thin films had an amorphous structure similar to the synthesized bulk glasses with limited crystallization. The results show homogenous and amorphous thin film structures with few polycrystalline formations.

High-Performance Hexagonal Tellurium Thin-Film Transistor Using Tellurium Oxide as a Crystallization Retarder

This study investigates the effect of oxygen plasma (PO) on the crystalline structure of tellurium (Te) thin films during reactive sputtering. Introduction of oxygen radicals suppresses uncontrolled rapid growth of hexagonal Te crystals, amorphizing the deposited Te thin film. This amorphous phase changes to the hexagonal phase upon alumina encapsulation. A 4-nm-thick Te transistor with a PO of 7% exhibits outstanding device performances, with a field-effect mobility up to 40.8 cm2V−1s−1 and an on/off current modulation ratio up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1\times 10^{{6}}$ </tex-math></inline-formula> . These behaviors originate from alleviated random polycrystallinity in the corresponding thin film. However, when PO increases above 7%, amorphization progresses further, and remnant oxygen ions hamper the growth of the hexagonal phase in Te thin film. Consequently, hole transport is degraded. This study suggests tellurium oxide as a crystallization retarder for high-performance p-channel Te transistors.

Model for contact formation of novel TeO2 containing Pb-free silver paste on n+ and p+ doped crystalline silicon

Silver (Ag) pastes are widely used in the global market for most solar cell architectures. Thereby, lead (Pb) is no longer wanted in productions for environmental reasons. In this work, a model for the contact formation between Pb-free, tellurium oxide (TeO2) containing screen-printable Ag pastes and silicon is presented. It is shown that Te plays a key role in this model. Te is not only an important part in etching the surface passivation layers with TeO2 dissolving the dielectric layer but also for a formation of the contacts with Te forming a compound consisting of Ag2Te. Using EDX mapping, local contact regions can be examined and interpreted for contact formation. The used paste system enables far more flexible paste mixturing leading to a novel developed commercial paste which is on a par with other pastes used in industry concerning the resulting contact properties. This is also demonstrated in this work by the very low contact resistivity of less than 1 mΩcm2 over a wide range of firing peak temperatures. It is additionally shown that good resistivities can be achieved on both n+- and p+-doped regions.

Assessment of Elongation Percentage, Tensile, and Tear Strength of Filler Particles

Introduction: We aimed to assess how the addition of nano tellurium oxide (TeO2) filler particles affected the elongation percentage, tensile strength, and tear strength of the maxillofacial silicone elastomer. Methods: Thirty samples were created by adding nano TeO2 powder (518.9 nm) at percentages of 0%, 3%, and 5% w/w into the RTV VST-50 silicon elastomer. Elongation percentage, tensile, and tear strength were assessed according to the specifications of ISO 37:2017 using a computerized universal testing device. Data were analyzed with one-way ANOVA and Tukey’s honest significant difference test using MedCalc 20.104. Results: There were statistically significant differences regarding elongation percentage, tensile, and tear strength among study groups (P &lt; 0.001). All of the post hoc comparisons showed statistically significant differences (P ≤ 0.002). Conclusion: The addition of 5% and 3% nano TeO2 filler particle significantly increases the elongation percentage, tensile strength, and tear strength of maxillofacial silicone in comparison with the control group, concentration-dependently.

Microscopic insight into structural and optical properties of glassy TeO2 derived from finite-cluster ab initio modelling

The paper reports on theoretical analysis of structural and non-linear optical properties of different size and shape TeO2 clusters using ab initio hybrid functional approximation to density functional theory. The obtained structural properties reveal uncommon structural units for crystal, which are common for amorphous tellurium oxide glass. The pair distribution function reproduces the experimental data in very good agreement, as well as the calculated phonon density and the Raman spectra. The finite field method was applied to evaluate the values of third order nonlinear susceptibility. The obtained values are in line with experimental data. This opens possibility to use such clusters to analyze the structural organization, vibrational and dielectric properties of the tellurium oxide glass.

Assessment of the Ecotoxicity of Ag, Bi, Te and Tl According to the Biological Indicators of Haplic Chernozem

Soil contamination with such rare heavy metals as silver (Ag), bismuth (Bi), tellurium (Te), and thallium (Tl) leads to disruption of its agricultural and ecological functions. Each of these rare heavy metals has a different level of soil toxicity, which affects the ecological state of the soil and its recovery degree estimated by biological indicators. The work objective is to assess the ecotoxicity of oxides and nitrates of silver, bismuth, tellurium, and thallium by biological indicators of Haplic Chernozem. Under the conditions of a laboratory simulation experiment, silver, bismuth, tellurium, and thallium were introduced into the samples of soil. The ecological state of the soil for each incubation period was assessed by the activity of soil enzymes (catalase and dehydrogenases), the intensity of seed development in polluted soil (the length of shoots and roots of winter wheat), and microbiological indicators (the total number of bacteria and Azotobacter sp. abundance). For 90 days, when contaminated with oxides of silver, bismuth, tellurium, and thallium, the most sensitive biological indicator was the length of wheat roots; when contaminated with nitrates, the total number of bacteria was the most sensitive biological indicator. The most informative biological indicator for contamination with both chemical forms of rare elements (silver, bismuth, tellurium, and thallium) was the Azotobacter sp. abundance. The most ecotoxic elements among those studied were thallium and tellurium, both in the form of oxides and nitrates. The results of the study may be useful for biomonitoring and diagnostics of the state of soils contaminated with silver, bismuth, tellurium, and thallium.

Correlation between mechanical, gamma shielding features and tellurium oxide concentrations in molybdenum aluminum strontium borate glass

This study investigates the effect of adding TeO2 instead of B2O3 in a glass system containing a fixed amount of Al2O3, MoO3, and SrO as modifiers. The present work included the impact of the addition of TeO2 on radiation and mechanical properties theoretically. The shielding properties were calculated based on XCOM data, and mechanical properties were computed based Makishima-Mackenzie’s model. The addition of TeO2 reduced the packing density gradually. Besides, Young’s longitudinal, shear, and bulk moduli showed the same behavior. In contrast, the density and shielding properties enhanced progressively with increasing TeO2 instead B2O3, like mass attenuation coefficient, transmission factor, effective atomic number, radiation protection efficiency, charged particle range, etc. It can be concluded that adding TeO2 reduced the glass elasticity and enhanced radiation shielding features, leading to potential utilization in the gamma and charged particle shielding scope.

Controlled Synthesis of Tellurium Nanowires.

One-dimensional tellurium nanostructures can exhibit distinct electronic properties from those seen in bulk Te. The electronic properties of nanostructured Te are highly dependent on their morphology, and thus controlled synthesis processes are required. Here, highly crystalline tellurium nanowires were produced via physical vapour deposition. We used growth temperature, heating rate, flow of the carrier gas, and growth time to control the degree of supersaturation in the region where Te nanostructures are grown. The latter leads to a control in the nucleation and morphology of Te nanostructures. We observed that Te nanowires grow via the vapour-solid mechanism where a Te particle acts as a seed. Transmission electron microscopy (TEM) and electron diffraction studies revealed that Te nanowires have a trigonal crystal structure and grow along the (0001) direction. Their diameter can be tuned from 26 to 200 nm with lengths from 8.5 to 22 μm, where the highest aspect ratio of 327 was obtained for wires measuring 26 nm in diameter and 8.5 μm in length. We investigated the use of bismuth as an additive to reduce the formation of tellurium oxides, and we discuss the effect of other growth parameters.

Visible light-induced degradation of organic dyes by niobium tellurium oxides ANbTeO6 (A = Rb, Cs) with β-pyrochlore structure

Niobium tellurium oxides ANbTeO6 (A = Rb, Cs) with β-pyrochlore structure were prepared via a solid-state reaction followed by ball milling. The photocatalytic activity of the compounds was investigated in the degradation of organic dyes under ultraviolet and visible light. The nanosized RbNbTeO6 demonstrated the highest photocatalytic activity in the degradation of methylene blue, which could be attributed to much more efficient adsorption of the dye onto the surface. It was found that the photocatalytic activity of the nanosized RbNbTeO6 photocatalyst is much higher than that of its structural analogues. This work presents a novel photocatalyst with high performance for the degradation of cationic dyes, and it affords a prototype to efficiently utilize solar energy.

Phase Transformations and Tellurium Recovery from Technical Copper Telluride by Oxidative-Distillate Roasting at 0.67 kPa

This paper presents the results of a study of phase transformations occurring in copper-telluride by-products during its processing of oxidation-distillate roasting at low pressure. The results show that copper telluride is oxidized through intermediate compounds to the most stable tellurate (Cu3TeO6) at low temperatures. The increase in the roasting temperature above 900 °C and the presence of an oxidizer favor the copper orthotellurate decomposition. Thus, the tellurium extraction rate is 90–93% at a temperature of 1000 °C, the oxidant flow rate is 2.2 × 10−2 m3/m2·s, and the roasting time is 60–90 min. One of the decomposition products is copper oxide alloy, which is the basis of the residue. The second product is tellurium in oxide form, which evaporates and then condenses in the cold zone of the condenser in crystalline form. The main constituent phase of the condensate is tellurium oxide (TeO2), which can be further processed during one operation to elemental chalcogen by thermal reduction or electrolytic method.

The Radiation Shielding Performance of Polyester with TeO2 and B2O3

In this research, polymers were fabricated through combining polyester, boron oxide (B2O3), and Tellurium oxide (TeO2). B2O3 has good neutron absorption and TeO2 is not only highly dense (5.670 g/cm3) but also environment-friendly, compared to PbO, as well as being a good photon absorber. The radiation protection features for five investigated samples were examined utilizing an HPGe detector and point sources Am-241, Cs-137, and Co-60. The accuracy of the experimental setup of this experiment was proven through the linear attenuation coefficient (LAC) values obtained from the theoretical (XCOM) and experimental (HPGe) values of the newly developed polymers. The attained results showed that the values of LAC decrease with increasing energy. Moreover, at low energy, a noteworthy increase was found for the LAC values with the addition of TeO2. Due to the increase in TeO2 content of the polymers, the value of the half value layer (HVL) decreases from 6.073–4.193 cm at energy 0.662 MeV, from 7.973–5.668 cm at energy 1.173 MeV, and 8.514–6.061 cm at energy 1.333 MeV. The values of the effective atomic number (Zeff) showed an improvement with the increase in TeO2 content in the polymers. For example, at energy 0.150 MeV, the Zeff values of the prepared sample followed this decreasing trend - PBT-40 &gt; PBT-30 &gt; PBT-20 &gt; PBT-10 &gt; PBT-0.