Tellurium Content Research Articles

Determination of selenium and tellurium concentrations in Pyrenean peridotites (Ariege, France): New insight into S/Se/Te systematics of the upper in mantle samples

Whole-rock concentrations of Se and Te were determined in 53 peridotite samples collected in orogenic bodies from the Eastern Pyrenees, including the Lherz massif (33 samples), the type-locality of lherzolite. Orogenic lherzolites tectonically emplaced into the continental crust escaped devolatilisation that may strongly alter concentrations of those volatile trace elements in basalt-hosted peridotite xenoliths. The Se and Te concentration ranges (< 3.5–100.7 ppb; < 1–11 ppb) are consistent with the few analyses of mantle samples yet available, yet extending to higher Se concentrations. In-situ analyses performed by LAM-ICPMS on base metal sulfides indicate that the Se budget is controlled by sulfides whereas a large fraction of Te (50 ± 30%) does not reside in sulfides. The missing fraction is accounted for by fractional crystallization of Pt–Pd tellurides from Cu–Ni sulfide melts. A maximum of one third of the S budget of Eastern Pyrenean peridotites was added by assimilation of crustal sulfides, which crystallized as pyrite. Disregarding those contaminated samples, some features of the Se and Te systematics (e.g. bivariate plots vs. fertility index) cannot be explained by partial melting processes. The best fit for 33 peridotites (mostly from Lherz) yields higher than chondritic S/Se (3.1213 ± 500; r 2 = 0.96) for near chondritic Se/Te (8.6 ± 2; r 2 = 0.9). Our study suggest that such superchondritic S/Se ratios are better explained by petrogenetic processes involving refertilization of harzburgitic lithosphere by metal (Cu,Ni)-rich sulfide melts precipitated along with clinopyroxene and Al-spinel from silicate melts en-route to the surface.

Structural, optical and electrical properties of ZnTe1−x Se x thin films

ZnTe1−x Se x films were deposited on glass substrates kept at 200 °C by the electron beam evaporation technique. These films exhibited cubic structure and the lattice parameter increased with increase of Tellurium concentration in the films which confirmed the solid solution formation. The grain size is found to increase with Te content. The dislocation density and lattice strain show a decreasing trend with increasing of Te content. Band gap values of 2.73 eV, 2.63 eV, 2.52 eV and 2.41 eV have been calculated for the films of composition ‘x’ = 0.2, 0.4, 0.6 and 0.8, respectively, which confirmed the formation of solid solution between ZnSe and ZnTe. Refractive index of the films increased from 2.535 to 2.826 as the concentration of Te increased. All the films showed high resistivity values. Laser Raman spectral studies of ZnTe1−x Se x revealed LO phonon frequencies whose values are located in between the LO phonon frequencies of ZnSe and ZnTe.

Structural and optical properties of Ag2SeTe nano thin films prepared by thermal evaporation

Semiconducting Ag2SeTe thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by XRD exhibiting no preferential orientation along any plane, however the films are found to have peaks corresponding to mixed phase. The XRD studies were used to calculate the crystallite size and microstrain of the Ag2SeTe films. The calculated microstructure parameters reveal that the crystallite size increases and micro strain decreases with increasing film thickness. The refractive index, dielectric constants and thereby the optical bandgap of the films were calculated from transmittance spectral data recorded in the range 400–1200 nm by UV–VIS-Spectrometer. The direct optical bandgap of the Ag2SeTe thin films deposited on glass substrates with different thicknesses 50–230 nm were found to be in the range 1.48–1.59 eV. The carrier density value is estimated to be around 9.8 × 1021 cm−1 for the film thickness of 150 nm. The compositions estimated from the optical band gap studies reveal a value of 0.75 for Tellurium concentration. These structural and optical parameters are found to be very sensitive to the thin film thickness.

Phase formation and selective oxidation of propane over MoVTeNbO x catalysts with varying compositions

The selective oxidation of propane to acrylic acid on MoVTeNbO x catalysts with varying concentrations of vanadium, tellurium and niobium was investigated. Catalysts containing M1 phase were obtained over the compositional range of MoV 0.14–0.22Te 0.1–0.2Nb 0.1–0.2O x . Vanadium containing sites in the M1 phase are drastically more active for propane activation than in other materials studied. The catalytic activity is directly correlated to its fraction in the overall material and in particular the M1 phase. High concentrations of tellurium induce the formation of the M2 phase decreasing so the overall activity of the catalysts. The intrinsic activity of the M1 phase is, however, independent of the tellurium concentration. Although the presence of the M1 phase is not a stringent requirement for the oxidative dehydrogenation of propane to propene, it is required to oxidize the intermediately formed propene with high selectivity to acrylic acid. The active sites for propane activation and propene oxidation are structurally coupled, because the ratio between the rates of the two reactions was always 1:25. Oxygen defect sites in mixed oxides seem to enhance interaction with acrylic acid and lead to decarboxylation and total oxidation.

X-ray diffraction and Raman spectroscopy on Gd 2(Ti 2− yTe y)O 7 prepared at high pressure and high temperature

A series of Te-substituted pyrochlores of stoichiometry Gd 2(Ti 2− y Te y )O 7 ( y ≤ 0.2) were prepared under high-pressure and high-temperature conditions and characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. X-ray diffraction and X-ray photoelectron spectroscopy studies revealed that the Te 4+ and Te 6+ ions occupy the Ti 4+sites; the percentage of the contribution of Te 6+ increases as tellurium content. These substitutions induce an increase of the volume of the TiO 6 octahedron due to the increase in the Ti–O(2) bond length, which preserves the oxygen positional parameter ( x 48f ) and the Gd–O(1) bond length. Results of Raman spectroscopy showed a significant shift to higher frequencies of the E g mode associated to the O(2) sublattice, as well an increase in the full-width-at-half-maximum intensity (FWHM) of the F 2g mode (O–Gd–O bending) as the level of Te substitution for Ti increases. These results are discussed and compared with those reported in the literature.

Speciation and determination of ultra trace amounts of inorganic tellurium in environmental water samples by dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

A simple and powerful method has been developed for the rapid and selective determination of Te(IV) and Te(VI), employing dispersive liquid–liquid microextraction combined with electrothermal atomic absorption spectrometry using palladium as permanent modifier. Under acidic conditions pH 1, only Te(IV) can form a complex with ammonium pyrrolidine dithiocarbamate (APDC) and therefore be extracted into fine droplets of carbon tetrachloride (extraction solvent) which are dispersed with ethanol into the water sample solution. After centrifugation, Te(IV) was determined in the sedimented organic phase while Te(VI) remained in the aqueous phase. Total inorganic tellurium was determined after the reduction of the Te(VI) to Te(IV). Te(VI) was calculated as the difference between the measured total inorganic tellurium and Te(IV) content. The effective parameters for improving the efficiency of microextraction process were investigated by using experimental and central composite designs. Under optimal conditions the enrichment factor was 125 and the calibration graph was linear in the range of 0.015–1 ng mL −1 with detection limit and characteristic mass of 0.004 ng mL −1 and 0.033 pg, respectively. The relative standard deviation for 0.5 ng mL −1 of tellurium measurement was 3.6% ( n = 6) at ash and atomization temperature, 900 and 2600 °C, respectively. The recoveries of spiked Te(IV) and Te(VI) to the environmental water samples were 89.6–101.3% and 96.6–99.1%, respectively. The accuracy is also evaluated by applying the proposed method to certified reference material (NIST SRM 1643e), for which the result was in a good agreement with the certified values reported for this CRM (95% confidence level).

The Region of gallium solubility in lead telluride films grown on silicon substrates

This work is aimed at finding the boundaries of the region of the existence of the solid solutions of Ga in PbTe films prepared on Si substrates with the use of the modified “hot wall” technique. The quantitative results on the composition of the Pb1-y GayTe films with a thickness of more than 1 µm indicate that the gallium concentration yGa in our samples ranges from 0.0004 yGa0.045, depending on the ratio of the partial pressures of the metallic components, which maybe specified by the temperature and composition of the Ga1–xPbx liquid melts. By varying the partial pressures of the metallic components and the chalcogen, we succeeded in synthesizing Pb1-yGayTe layers with a Te concentration ranging from 0.495 to 0.515 mol %. According to the results of a complex investigation with the use of X-ray diffraction, scan ning electron microscopy, and local X-ray spectrum analysis, the region of the existence of homogeneous Pb1 - y GaTe films is substantially narrower than the specified composition range: the limiting Ga concentration in these samples is no more than yGa = 0.011 ± 0.0005. It has been shown that the study of gallium solubility in PbTe should include not merely a quasi-binary PbTe-GaTe section, but also PbTe-Ga2Te3 and PbTe-Ga2Te5 polythermic sections. As indicated by the experimental data, the homogeneity region of the solid solutions of gallium in lead telluride is asymmetric with respect to the quasi-binary PbTe-GaTe section. It has been found that the deviation of the Pb1-yGayTe films from stoichiometry toward excessive concentration of tellurium promotes increased solubility of gallium in the lead telluride matrix.

Low temperature synthesis of thiol‐functionalized CdTe nanoclusters with different tellurium contents

AbstractIn recent years thiol‐functionalized cadmium telluride nanoparticles act as a core layers for obtaining high photovoltaic efficiency in conjugated polymer/inorganic nanocrystal solar cells and also provide easy tuning of quantum size effect by varying thiol groups and processing temperature. In this work, thiol functionalized CdTe nanoclusters were prepared for different tellurium concentrations at low temperature and its impact has been discussed. Structural parameters estimated by X‐ray diffraction revealed hexagonal phases at lower tellurium concentration and cubic phase at higher tellurium concentrations. Surface morphology of the samples analyzed by transmission electron microscopy, exhibited cluster type of morphology. Optical band gap energy estimated by diffused electron microscopy showed an increase with Te content and band edge emission has been observed in the photoluminescence spectra of CdTe nanoclusters around 620 nm. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thermal and optical analysis of Te-substituted Sn–Sb–Se chalcogenide semiconductors

Bulk amorphous samples of Te-substituted Sn10Sb20Se70−XTeX (0≤X≤12) were prepared using a melt quenching technique. Calorimetric studies of the samples were performed using differential scanning calorimetry (DSC) and the glass transition temperature and crystallization temperature were evaluated from DSC scans. The glass transition temperature Tg exhibits a sharp decrease for small Te substitution of X=2, thereafter increases with increase in Te content up to X=10, and then decreases for further Te substitution. The apparent activation energy for glass transition and the activation energy for crystallization were calculated using Kissinger, modified Kissinger, and Matusita equations. The change in glass transition temperature Tg has been explained based on the bond formation energy of different heteropolar bonds. The optical band gap of thermally evaporated thin films of Sn10Sb20Se70−XTeX (0≤X≤12) was calculated from reflectance and transmittance data. The optical band gap variation with tellurium content exhibits a sharp decrease for an initial tellurium substitution of X=2 similar to that of the glass transition temperature and thereafter a peak is observed in optical band gap around X=4 composition.

Effect of tellurium substitution in Sn10Sb20Se70−XTeX(0 &lt;X&lt; 12) amorphous chalcogenide system

The as-prepared samples of Sn 10 Sb 20 Se Te X chalcogenide system were amorphous as evidenced by X-ray diffraction and Differential scanning calorimetry studies. The different crystalline phases emerged in annealed Sn 10 Sb 20 Se Te X samples have been identified. Glass transition temperature T g of the as-prepared samples decreases sharply with tellurium substitution upto 2 at% and then it starts increasing upto 10 at% and decreases again on further substitution of tellurium. The change in glass transition temperature T g has been explained based on bond formation energy of different heteropolar bonds and crystalline phases obtained in the annealed samples with different tellurium contents.

Trace elements in hemodialysis patients: a systematic review and meta-analysis

BackgroundHemodialysis patients are at risk for deficiency of essential trace elements and excess of toxic trace elements, both of which can affect health. We conducted a systematic review to summarize existing literature on trace element status in hemodialysis patients.MethodsAll studies which reported relevant data for chronic hemodialysis patients and a healthy control population were eligible, regardless of language or publication status. We included studies which measured at least one of the following elements in whole blood, serum, or plasma: antimony, arsenic, boron, cadmium, chromium, cobalt, copper, fluorine, iodine, lead, manganese, mercury, molybdenum, nickel, selenium, tellurium, thallium, vanadium, and zinc. We calculated differences between hemodialysis patients and controls using the differences in mean trace element level, divided by the pooled standard deviation.ResultsWe identified 128 eligible studies. Available data suggested that levels of cadmium, chromium, copper, lead, and vanadium were higher and that levels of selenium, zinc and manganese were lower in hemodialysis patients, compared with controls. Pooled standard mean differences exceeded 0.8 standard deviation units (a large difference) higher than controls for cadmium, chromium, vanadium, and lower than controls for selenium, zinc, and manganese. No studies reported data on antimony, iodine, tellurium, and thallium concentrations.ConclusionAverage blood levels of biologically important trace elements were substantially different in hemodialysis patients, compared with healthy controls. Since both deficiency and excess of trace elements are potentially harmful yet amenable to therapy, the hypothesis that trace element status influences the risk of adverse clinical outcomes is worthy of investigation.

Thermal Conductivity Measurements and Modeling of Phase-Change Ge2Sb2Te5 Materials

Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high-storage-density nonvolatile random access memory, due to its much longer cycle life (∼1013) and fast data access time (∼100 ns) compared with the existing flash memory technology. In this article, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability of phase change–based data storage devices and systems. We present thermal conductivity data for a 40-nm-thick Ge2Sb2Te5 phase-change layer in both amorphous and crystalline states using electrical resistance joule heating and thermometry techniques. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions to the total thermal conductivity as a function of tellurium concentration, crystalline structures, and temperature.

Formation of CdSxTe1–x at the p‐n junction of CdS‐CdTe solar cells

AbstractThe formation of ternary CdSxTe1–x alloys during CdTe solar cell production is quantitatively investigated using optical and quantum efficiency measurements. Both the diffusion of sulphur into the CdTe and of tellurium into the CdS film are analysed in the context of film thicknesses and the activation step used in CdTe solar cell processing. We present a method of determining the tellurium content in the CdS layer from EQE measurements. The tellurium content is limited to small values and depends on the CdS thickness. A CdSxTe1–x phase of several 100 nm thickness is generated in the CdTe film during the activation step. This phase changes the optical bandgap in the depletion region and gains importance in cells with thin absorbers. The comparison of solar cells with and without CdS layer illustrates the crucial role of the CdS buffer layer for the p‐n junction. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Speciation and determination of trace inorganic tellurium in environmental samples by electrodeposition-electrothermal atomic absorption spectroscopy

A simple speciation method using selective electrodeposition with a mercury coated electrode in hydrochloric acid medium was developed for the speciation and determination of trace amounts of Te (IV) and Te (VI) in water samples by electrothermal atomic absorption spectroscopy (ETAAS). Bottled drinking water, river water and sea water samples were spiked with trace amounts of Te (IV) and Te (VI) and the spiked solutions were subjected to an electrodeposition process prior to determination by ETAAS. The method is based on the selective reduction of the tellurium (IV) at an uncontrolled applied potential (2.0 V) on the mercury coated electrode. In acidic media (1.0 M HCl solution) only Te (IV) can be electrodeposited onto the mercury electrode surface and separated Te (VI) remained in solution. The electrode was withdrawn from the solution and the spent electrolyte containing Te (VI) was measured by ET-AAS. Te (IV) was calculated as the difference between the measured total tellurium and Te (VI) content. The spiked recovery value varied between 93 to 97%. The experimental parameters of ET-AAS such as ashing and atomization temperature, ashing and atomization time, type and amount of modifier were optimized using a central composite design after a 2n−1 fractional factorial experimental design. The obtained detection limit and characteristic mass for Te (IV) were 2.0 µg L−1 and 20 pg, respectively. The application of the proposed method was investigated on water samples analysis.

High quality p-type ZnO film grown on ZnO substrate by nitrogen and tellurium co-doping

AbstractNitrogen and tellurium co-doped ZnO (ZnO:[N+Te]) films have been grown on (0001) ZnO substrate by plasma-assisted molecular beam epitaxy. The electron concentration of tellurium doped ZnO (ZnO:Te) gradually increases, compared that of undoped ZnO (u-ZnO). On the other hand, conductivity of ZnO:[N+Te] changes from n-type to p-type characteristic with a hole concentration of 4×1016 cm-3. However, nitrogen doped ZnO film (ZnO:N) still remain as n-type conductivity with a electron concentration of 2.5×1017 cm-3. Secondary ion mass spectroscopy reveals that nitrogen concentration ([N]) of ZnO:[N+Te] film (2×1021 cm-3) is relatively higher than that of ZnO:N film (3×1020 cm-3). 10 K photoluminescence spectra shows that considerable improvement of emission properties of ZnO:[N+Te] with an emergence of narrow acceptor bound exciton (A°X, 3.359 eV) and donor-acceptor pair (DAP, 3.217 eV), compared with those of u-ZnO. Consequently, high quality p-type ZnO with high N concentration is realized by using Te and N co-doping technique due to reduction of Madelung energy.

Effect of doping and heat treatment on the mechanical parameters of ZnSe(1 − x)Te x crystals grown from the melt

The mechanical properties of crystals of ZnSe(1 − x)Tex (0 < x < 1.3 wt %) solid solutions are investigated using the indentation method. The breaking points of doped and undoped crystals are measured by the uniaxial compression method. It is revealed that the microhardness anisotropy coefficient for crystals with a tellurium dopant content of ∼0.3 wt % is equal to unity. A change in the tellurium content in the solid solutions from 0.2 to 1.3 wt % leads to a linear increase in the microhardness by 23%. The brittle strength of the ZnSe and ZnSe(1 − x)Tex crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe(1 − x)Tex crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.

Composition dependent electrical switching in [formula omitted] glasses–the influence of network rigidity and thermal properties

Electrical switching investigations and supportive thermal studies have been undertaken on semiconducting chalcogenide Ge x Se 35− x Te 65 ( 18 ≤ x ≤ 25 ) glasses prepared in bulk form. An interesting composition dependent change (memory to threshold) has been observed in the switching behavior of these glasses across the stiffness/rigidity percolation threshold (RPT) at x = 20 ( 〈 r 〉 = 2.40 ). Also, the rigid Ge x Se 35− x Te 65 glasses are found to retain the threshold behavior for hundreds of switching cycles. Further, the switching voltage of Ge x Se 35− x Te 65 glasses has been found to exhibit an abrupt increase at the RPT. Alternating Differential Scanning Calorimetric studies indicate that the Ge x Se 35− x Te 65 glasses with higher tellurium concentrations exhibit two crystallization exotherms, which coalesce at the composition x = 20.5 (average coordination 〈 r 〉 = 2.41 ), which also marks the beginning of melting endotherms. The relatively low crystallization temperature ( T c 1 ) , along with the floppy structural network aids easy phase change in Ge x Se 35− x Te 65 glasses with x < 20 , causing them to exhibit memory switching. The moderately higher crystallization temperature (300–330 ∘C) and the stabilizing influence of network connectivity & rigidity are plausibly responsible for the threshold behavior seen in the rigid Ge x Se 35− x Te 65 glasses.

Investigation of Modified Bridgman Grown CdTe x Crystals and Their Characterization

Growth procedure was modified with off-stoichiometric charge using excess tellurium solution (different Te composition 0.9, 1.1, 1.2, and 1.3 weight percentages in the initial charge). Graphitic carbon coating of the inner wall of the ampoule was carried out. The rotation of the ampoule with the molten charge was carried out before lowering the same for crystal growth. The grown crystals were characterized by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), photoluminescence, and chemical etching studies. Increasing tellurium content in the charge in excess of 1.2 weight percent lead to cracks and twinning. The off-stoichiometric melt grown crystals crystallize in zinc blende structure with lattice parameter 6.482 Å. Excess tellurium content in the crystal decreases the intensity of the prominent peak along the (111) direction in the XRD spectrum. The defect levels introduced by Te precipitates for various tellurium rich compositions in CdTe x crystals are identified from the photoluminescence spectra. The off-stoichiometric charge composition influences enormously the defect density and the crystalline quality of the grown crystals. The results on the optimization of the growth procedure and influence of off-stoichiometric compositions are discussed.

Compositional dependence of the optical properties of amorphous Se100– x Te x thin films

Thin films of amorphous Se100 –x Te x with different compositions (x = 10, 20, 30 and 40 at%) were deposited on glass substrates by thermal evaporation. Transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 17 896 (1984)], using of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction plus film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model [Phys. Rev. B 3 1338 (1971)]. The optical band gap was determined from the spectral dependence of the absorption coefficient using the Tauc formula [in The Optical Properties of Solids, edited by F. Abeles (North Holland, Amsterdam, 1970), p. 227]. The refractive index increases and the optical band gap decreases with increasing tellurium content.

Nonlinearity of refractive index in glasses based on heavy metal oxides with different lead and tellurium contents

We have studied the nonlinearity of the refractive index at a wavelength of 1.08 µm for optical lead silicate and lead phosphate tellurite glasses of different compositions. We have shown that the nonlinear refractive index n2 increases as the lead content increases in lead silicate glasses and as the tellurium content increases in lead phosphate tellurite glasses, where the latter are typically have higher values of n2, as high as 24·10−13 cgs units (47·10−16 cm2/W), and lower Rayleigh losses. We have established a correlation between the nonlinear refractive index and the microstructure of the studied glasses. The highly nonlinear glasses are distinguished by extensive fluctuations in the heavy metal oxide concentration which are “frozen” during cooling of the glass melt.