Te Anions Research Articles

Manipulating lattice distortion to promote average thermoelectric power factor in metavalently bonded AgBiSe2

Local off-centering of atoms generally leads to high Grüneisen parameters and thus low lattice thermal conductivity, which is considered to be favorable for thermoelectric materials. Nevertheless, such severely distorted local structures may cause strong scattering for electrons and poor electrical performance. Here we demonstrate the relationship between thermoelectric properties and local structure in AgBiSe2 dual alloying with PbTe. It is disclosed that the introduction of Te anions in cubic (AgBiSe2)1−x(PbTe)x can release the distortion index of Bi/Ag/Pb cations in a octahedral shell, which substantially improves the local symmetry and meanwhile the weighted mobility in relevant alloys. More interestingly, it is elucidated that dually-alloyed AgBiSe2 displays a metavalent bonding character, first time reported in n-type cubic TE materials, as collectively verified by atomic coordination number, anomalously increased optical dielectric constant, moderate electrical conductivity, and large Grüneisen parameter. Consequently, a record-high average power factor of 0.52 mW m−1 K−2 between the measurement temperature interval, and a peak zT value of 0.92 at 800 K is obtained for metavalently bonded (AgBiSe2)0.75(PbTe)0.25.

Impact of tellurium as an anion dopant on the photovoltaic performance of wide-bandgap Cu(In,Ga)Se2 thin-film solar cells with rubidium fluoride post-deposition treatment

The development of wide-bandgap Cu(In,Ga)Se2 thin films is crucial in order to reach the theoretical Shockley–Queisser limit values in single-crystal solar cells. However, the performance of solar cells based on wide-bandgap thin film absorbers has lagged significantly compared to that of their narrow-bandgap counterparts. Herein, we develop a feasible strategy to improve the photovoltaic performance of wide-bandgap Cu(In,Ga)Se2 chalcopyrite thin-film solar cells by simultaneously doping with both RbF PDT and Te2− anions as dopants in the absorber layer during the three-stage co-evaporation process. Besides inducing significant change in the GGI gradient, the synergistic effect of the Te2− anion dopant is rather beneficial in terms of controlling grain size, defects in grain boundaries, and charge carrier lifetime for encouraging charge separation and extraction, which contributes to simultaneously boosting short-circuit current density and fill factor. Te-poor devices afford an impressive efficiency of 9.58%, compared to 6.43% for control devices. More importantly, the efficiency and Voc values obtained for wide-bandgap-based thin-film solar cells containing Te anions were the highest compared to their counterparts as reported in the literature. These results demonstrate the role of Te2− anions in wide-bandgap absorber thin films on the photovoltaic performance of thin-film solar cells and the potential of this approach for use in reasonable and effective design of highly efficient wide-bandgap thin-film solar cells.

Synthesizability of transition-metal dichalcogenides: a systematic first-principles evaluation

Transition metal dichalcogenides (TMDs) are a class of materials with various useful properties, and it is worthwhile to have a thorough evaluation of the characteristics of the TMDs, most importantly, their structural stability and exfoliability, in a systematic fashion. Here, by employing high-throughput first-principles calculations, we investigate the vast phase space of TMDs, including 16 bulk phases and 6 monolayer phases for all possible TMD combinations [comprising (3d, 4d, 5d) transition-metal cations and (S, Se, Te) anions], totaling 1386 compounds. Through the ‘bird-view’ of the as-large-as-possible configurational and chemical space of TMDs, our work presents comprehensive energy landscapes to elucidate the thermodynamic stability as well as the exfoliability of TMDs, which are of vital importance for future synthesis and exploration towards large-scale industrial applications.

LaTe1.82(1): modulated crystal structure and chemical bonding of a chalcogen-deficient rare earth metal polytelluride.

Crystals of the rare earth metal polytelluride LaTe1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour-assisted crystallization with iodine. The two-dimensionally incommensurately modulated crystal structure has been investigated by X-ray diffraction experiments. In contrast to the tetragonal average structure with unit-cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group-subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e. Pmmn(α,β,1/2)000(-α,β,1/2)000 (No. 59.2.51.39) and Pm21n(α,β,1/2)000(-α,β,1/2)000 (No. 31.2.51.35), with modulation wave vectors q1= αa* + βb* + 1/2c* and q2 = -αa* + βb* + 1/2c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI-D)-based bonding analysis on three different approximants. The temperature-dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV.

Crystallographic Analysis of the Atomic Configurations in the Cubic (Fm$$\bar {3}$$m) Structural Type K4Ag18Te11 and Related Structures

The K4Ag18Te11, Tl4Ag18Te11, and BaHg11 cubic structures have been crystallographically analyzed within the study of the “symmetry–stability of crystalline materials” problem. The high symmetry of these structures is initiated by the local symmetry of templates, which are cuboctahedra composed of twelve Ag polyhedra around a Te anion (for the former two compounds) and twelve Hg polyhedra around a central Hg atom (for the latter compound). Similar cuboctahedra, consisting of K, Tl, and Ba cations, are formed in the second coordination sphere. The role of symmetry in the reduction of atomic degrees of freedom, which provides the structure stability, has been estimated. The qualitative stability criteria are formulated.

Changes in the Nature of Chemical Bonding in Solid Solutions between Copper and Silver Chalcogenides

The electron density distribution in solid solutions between the high-temperature (cubic) phases of copper and silver chalcogenides has been assessed within the density-functional approach using pseudopotential calculations implemented in the Quantum Espresso program package. The results indicate that Cu–Ag cation substitutions and S–Se–Te anion substitutions lead to a reduction in electron shell overlap.

Sample Digestion and Combined Preconcentration Methods for the Determination of Ultra-Low Gold Levels in Rocks.

The gold abundance in basic rocks, which normally varies between 0.5 and 5 ppb, has served as a very important indicator in many geoscience studies, including those focused on the planetary differentiation, redistribution of elements during the crustal process, and ore genesis. However, because gold is a monoisotopic element that exhibits a nugget effect, it is very difficult to quantify its ultra-low levels in rocks, which significantly limits our understanding of the origin of gold and its circulation between the Earth crust, mantle, and core. In this work, we summarize various sample digestion and combined preconcentration methods for the determination of gold amounts in rocks. They include fire assay, fire assay combined with Te coprecipitation and instrumental neutron activation analysis (INAA) or laser ablation inductively coupled plasma mass spectrometry, fusion combined with Te coprecipitation and anion exchange resins, dry chlorination, wet acid digestion combined with precipitation, ion exchange resins, solvent extraction, polyurethane foam, extraction chromatography, novel solid adsorbents, and direct determination by INAA. In addition, the faced challenges and future perspectives in this field are discussed.

Crystal structure of the high-temperature form of the trisulfide Cs2S3 and the (3+1)D modulated structure of the telluride K37Te28

Abstract The high-temperature polymorph of the trisulfide Cs2S3, which has been synthesized from Cs2S2 and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P21/c, a=999.97(4), b=1029.30(5), c=2642.07(12) pm, β=90.083(2)°, Z=16, R1=0.0324). The structure contains four crystallographically independent angled S 3 2 − ${\rm{S}}_3^{2 - }$ trisulfide ions with S–S distances of 205.7–208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.53+3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc21, K2S3-type structure) and the two polymorphs differ mainly in the orientation of the S3 groups. The second title compound, K37Te28, was synthesized from stoichiometric melts of the elements. It forms a complex (3+1)D modulated tetragonal structure (space group I41/amd (00σ 3)s0s0, q=(0, 0, 0.5143), a=1923.22(2), c=2626.66(4) pm, Z=4, R1all=0.0837). According to K37Te28=K37[Te(1X)]8[Te(2X)2]6[Te(3X)8] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)]2− are coordinated by 9/10 K+ cations. Three [Te(2X)2]2− dumbbells (d Te-Te=277.9/286.4 pm) are arranged to ‘hexamers’. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K+ cations, results in the decomposition of the [Te(3X)8]2 chain in a sequence |:Te3–Te2–Te2–Te3–Te2–Te2–Te2:| of dumbbells Te2 2− (d Te–Te=304 pm) and hypervalent linear trimers Te3 4− (d Te–Te=325 pm).

Removal of Te and Se anions in alkaline media in presence of cyanide by quaternary ammonium salts

Precious metals are currently associated with selenium (naumannite, Ag2Se) and tellurium (calaverite, AuTe2; sylvanite, (Au,Ag)2Te4) to form species refractory to cyanidation. The aim of this preliminary work was to study the use of the solvent extraction technique to recover tellurium and selenium ions from a synthetic solution similar to the cyanidation effluents to recycle the free cyanide back to the process. For the extraction of the Se and Te anions, the use of quaternary amines as extractants was evaluated (tallow trimethyl ammonium chloride, Quartamin TPR; hexadecyl trimethyl ammonium chloride, Amine F; and trioctyl methyl ammonium chloride, Aliquat 336) employing nonylphenol as a modifier in the organic phase (iso-octane). The results obtained showed that the extraction was strongly affected by the pH and that it was possible to recover up to 83% of Se and 10% of Te with Quartamin TPR from two synthetic solutions containing 23 mg/L of Te and 20 mg/L of Se with a molar cyanide:metal ratio of 1:4 at pH 11, a ratio of aqueous/organic (A/O) = 1 (V/V) and an extractant concentration of 0.022 mol/L. A maximum distribution coefficient (D) of 4.97 was obtained at pH 11. The McCabe-Thiele diagram indicates that two theoretical extraction stages are necessary to obtain a good extraction of Se complexes using Quartamin TPR.

Electronic structure and excited states of molecular crystals of antimony and tellurium hexahalogenides

The article examines the electronic structure and orbital nature of luminescence excitation in a series of molecular crystals with the general formula E n AX6, where E n are organic and inorganic cations (diphenylguanidinium, guanidinium, and cesium); n is the number of cations; AX6 are Te(IV) and Sb(III) anions; X are the atoms of halogens Cl or Br. The electronic structure of these molecular crystals is determined from the data of X–ray photoelectron spectroscopy of the core and valence levels and еру quantum chemical modeling фе the density functional theory level together with the previously obtained single crystal X–ray diffraction data.

Polarography of Te (IV) Anions in Neutral Solutions in Presence of 2,2'- Dipyridyl and Fe(dipy)3 2+ - Complexes

<p>The electroreduction of Te (IV) ions in neutral non-buffer solutions containing 2,2'-dipyridyl (4⋅10<sup>-5</sup>- 4⋅10<sup>-3</sup> M) or tris-dipyridyl iron (II) complexes is studied by the polarographic method. NaF (0.01-0.5 M) or NaNO<sub>3</sub> (0.1-1 M) are used as supporting electrolytes. The mechanism of electrochemical reactions of Te (IV) anions on mercury electrodes in the presence of the additives is discussed. The electroreduction of Te (IV) anions is shown to proceed through electron transfer and proton addition. The obtained results point to a considerable influence of electric double layer structure on electrochemical reactions of Te (IV) ions in the presence of inorganic and specifically adsorbed organic compounds in the electrolyte. It is shown, that 2,2'-dipyridyl does not form complexes with Te (IV) anions. Having been adsorbed on the surface of mercury electrode, 2,2'-dipyridyl complexes increase negative <em>Ψ</em>'-potential that results in a shift of Te (IV) electroreduction wave to more negative potentials and decrease in the current of Te (IV) wave and peak at -1.19 V. It is shown that 2,2'-dipyridyl molecules at <em>ε</em> > 0, (<em>ε</em> – charge of an electrode) are adsorbed in plane orientation, and at ε < 0, plane or vertical. Vertically adsorbed molecules cause a significant decrease in the double layer capacitance. At negative potentials orientation of 2,2'-dipyridyl molecules changes from plane to vertical with the increasing 2,2'-dipyridyl concentration. This change of orientation results in a typical maximum capacitance emerging in the potential range of -0.7 to -1.2 V. It is shown that the supporting electrolyte, 2,2'-dipyridyl and Fe(dipy)<sub>3</sub> <sup>2+</sup> have influence on the electroreduction of Te (IV) anions in neutral non-buffer solutions through a change in the <em>Ψ</em>'-potential of mercury electrode.</p>

Halide-Free Synthesis of Hydrochalcogenide Ionic Liquids of the Type [Cation][HE] (E=S, Se, Te).

We present the synthesis and thorough characterization of ionic liquids and organic salts based on hydrochalcogenide HE(-) (E=S, Se, Te) anions. Our approach is based on halide-, metal-, and water-free decarboxylation of methylcarbonate precursors under acidic conditions, resulting from the easily dissociating reagents H2 E. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy, thermal and single-crystal XRD analyses. The hydrosulfide salts were investigated with respect to their ability to dissolve elemental sulfur in varying stoichiometry. Thus-prepared polysulfide ILs were also analyzed by UV/Vis spectroscopy and cyclic voltammetry.

On-line I−/Te− separation for the AMS analysis of 125I

The isobar separator for anions (ISA) was used together with a 3MV tandem accelerator mass spectrometer (AMS) to demonstrate the real time (on-line) separation of Te− from I−. Following the ion source mass spectrometry and major retardation to tens of eV, the ISA uses a radiofrequency quadrupole (RFQ) ion guide to confine and direct I− and associated Te− isobar anions through a gas-reaction cell, where chemical reactions occur at eV energies with the electronegative gas NO2. Anions are subsequently reaccelerated out of the ISA to near original ion source extraction energies for AMS analysis. At 5mTorr NO2 in the ISA gas-reaction cell, 125Te− was observed to be attenuated by a factor of ∼107 as compared to 127I− that did not experience significant (<50%) losses. A comparative test using 37Cl− and 32S− (having similar chemical properties to iodine and tellurium) showed a 32S− attenuation of >107 relative to 37Cl− under the same ISA–AMS conditions. The preferential destruction of Te− (and S−) at eV energies in the ISA is likely due to a larger favorable destruction cross-section with NO2. This study is the first demonstration of I–Te anion separation for AMS, and makes possible the use of 125I, free of the contaminant 125Te isobar after suitable sample purification, for future 129I/125I carrier-free analyses of natural samples at ultra-low trace levels.

Flux Dynamics in Iron-Based Superconductors

The newly discovered iron-based superconductors share a common layered structure. After the iron pnictide (1111) family, other iron-based superconductors such as the iron chalcogenides FeTe1 - xSex (11) family have been synthesized. The latter system, characterized by a simple crystal structure, represents an interesting reference system. Indeed, all iron-based superconductors have a stacked structure composed of a layer of iron atoms linked by tetrahedrally coordinated pnictogens (P, As) or a chalcogen (Se, Te) anion: the active layer. The latter is either simply stacked together, as in the FeSe (11), or separated by spacer layers with alkali (e.g., Li), alkaline earth (e.g., Ba), or rare earth oxides/fluorides. In this contribution, we present an ac multiharmonic susceptibility study of the flux dynamic in representative 1111 and 11 iron-based superconductors. Data analysis has been performed in the glass-weak pinning scenario. In particular, the comparison of the third harmonic components vs. temperature and magnetic field returned information on pinning strength and dimensionality. Although in the presence of large thermal fluctuations, because of the high Tc, susceptibility data points out a three-dimensional flux dynamic and, unexpectedly, an increase of the pinning amplitude in the Fe-based superconductor systems where the spacer layer is present.

Wheel-shaped indium telluride nanoclusters co-crystallized with metal-phenanthroline complexes

Two wheel-shaped In18Te30 clusters with M-phen complex cations, [M(phen)3]2[In18Te30(dapn)6]·2Hdapn·dapn (M=Fe(II), and Ni(II), dapn=1.3-diaminepropane), were prepared. The In18Te30 anion shows a double-layered ring structure that assembled by six In2Te6 subunits and six InTe3N tetrahedra. The size of the wheel-shaped clusters is about 1.6nm. In the crystals clockwise and anticlockwise complex cations [M(phen)3]2+ are coupled through π⋯π interaction forming a dimer structure and the dimers are interacted with the clusters via C⋯Te (about 3.60Å) short contacts. The sizes of the dimer cation and the anion are well compensated in crystal packing. Although there is wider range absorption of the In–Te anion, the MLCT transition of the Fe-phen cation still contributes to the low energy absorption.

A Bismuth‐Stabilized Metal‐Rich Telluride Lu9Bi≈1.0Te≈1.0 – Synthesis and Characterization

AbstractSynthetic reactions aimed at bismuth incorporation into rare‐earth‐metal‐rich tellurides yielded Lu9Bi≈1.00Te≈1.00 over a small range of compositions, but no analogues with Gd, Tb, Er, or Y. A single‐crystal X‐ray diffraction analysis gave the composition Lu9Bi0.99(3)Te1.01 in the acentric orthorhombic space group Cmc21 at ambient temperature. This is isostructural with the re‐refined Sc9Te2 earlier reported in a monoclinic Cc structure. Lu9Bi≈1.00Te≈1.00 represents the first ternary compound in this structure type and the third lutetium‐richest compound after Lu8Te and Lu7Te. The structure contains 3 × 3 columns of Lu in the form of condensed distorted trans‐edge‐sharing octahedral chains along a. The Te and Bi anions lie within tricapped trigonal prisms of Lu. Generally shorter Lu–Lu interactions lie in the interior of 3 × 3 metal columns compared with those on the periphery for which fewer Lu–Lu interactions and polar covalent bonding with neighboring tellurium weaken Lu–Lu bonding. Limiting Lu–Lu distances around 3.18 Å are by far the shortest among reduced lutetium tellurides. LMTO‐type ab initio electronic structure calculations reveal a metallic nature and show that strong polar bonding of Lu to both the more electronegative Bi and Te leaves Lu relatively oxidized, many 5d states falling above the Fermi level. Stronger Lu–Lu bonding within the metal columns is also indicated by their larger individual Hamilton populations. The isostructural Lu9SbTe and Sc9BiTe were also shown to exist according to powder data.

An Unusual Binary Phosphorus−Tellurium Anion and Its Seleno- and Thio- Analogues: P4Ch22− (Ch = S, Se, Te)

We present an unusual discrete P-Te anion, P(4)Te(2)(2-), which is readily obtained by the oxidation of white phosphorus with Te(2)(2-) in N-methyl imidazole at ambient temperature. According to the (31)P and (125)Te NMR spectra, the anion P(4)Te(2)(2-) had a bicyclo[1.1.0]tetraphosphane ("butterfly") structure with the tellurium atoms in the exo positions. The anion was remarkably stable at ambient temperature and disproportionated only slowly with the formation of elemental tellurium. P(4)Te(2)(2-) is the first P-Te anion with a bicyclo[1.1.0]tetraphosphane structure. When Se(2)(2-) or S(2)(2-) was reacted with white phosphorus, the analogous seleno- and thiophosphate anions P(4)Se(2)(2-) and P(4)S(2)(2-) were formed, thus completing the series of phosphorus-chalcogen anions P(4)Ch(2)(2-) (Ch = S, Se, Te). The synthesis of P(4)Te(2)(2-) demonstrated that binary P-Te anions do exist as stable species in solution.

A New Type of 1-D Thioindates, [M(en)3]0.5[InS2] (M = Co, Ni), Synthesized by Solvothermal Reaction

Two thioindates [M(en)3]0.5InS2 [en = ethylenediamine; M = Ni (1), Co (2)] were prepared by the reaction of In2S3, Ni (or Co) and S under solvothermal conditions, and their crystal structures have been determined. Both compounds are isostructural and crystallize in the orthorhombic space group Cmcm. The crystal structures consist of a new type of 1-D sinusoidal chain, which complements the reported I - III types of 1-D [InQ2 −]n (Q = S, Te) anions built from InQ4 tetrahedra. The band gaps of 3.47 eV for I and 3.31 eV for 2 have been derived from optical absorption spectra.

Exciton photoluminescence, photoconductivity and absorption in GaSe 0.9Te 0.1 alloy crystals

The photoluminescence, photoconductivity and absorption in GaSe 0.9Te 0.1 alloy crystals have been investigated as a function of temperature and external electric field. It has been observed that the exciton peaks shift to lower energy in GaSe 0.9Te 0.1 alloy crystals compared to GaSe crystals. The long wavelength tails of interband photoluminescence, photoconductivity and absorption spectra are determined by the free exciton states and show an Urbach–Martienssen-type dependence to the photon energy. The maxima of the extrinsic photoluminescence and photoconductivity spectra were found to be determined by the acceptor centers with an energy of E A= E V+0.19 eV formed by the polytypism and defects complexes that include Se and Te anions.

Phosphine Selenide Arenetellenyliodide Complexes and Telluroselenophosphonium Salts

Trialkylphosphine selenides tBu n iPr3− n PSe (n = 3, 2, 1, 0) and bidentate phosphine selenides (dppmSe2, dppeSe2) react with arenetellurenyl iodides (RTeI) furnishing complexes tBu n iPr3− n PSeTe(R)I (R = p-tolyl, p-anisyl, mesityl [Mes]), dppm[SeTe(Mes)I]2 and dppe[SeTe(Mes)I]2 that contain Se-Te(R)-I moieties (10-Te-3). Dppe[SeTe(Mes)I]2 exhibits supramolecular soft-soft interactions by “T-stacking” of the Se-Te(R)-I functions in the solid. When trialkylphosphine selenides tBu n iPr3− n PSe react with two equivalents of RTeI, novel trialkyl(aryltelluroseleno)phosphonium diiodotellurate(II) salts are formed. In solid [(tBu2iPrPSeTe-p-Tol)+(p-TolTeI2)−] the Te atom from the (p-TolTeI2)−anion behaves as soft donor towards the formally uncharged Te atom in the cation (tBu2iPrPSeTe-p-Tol)+exhibiting a novel type of Te…Te anion → cation donor-acceptor interaction (Te…Te 318 pm). Loss of mesityl groups in course of reactions with MesTeI led to a unique iodotelluroselenophosphonium salt {[(iPr3PSeTeI)+]2(TeI6)2−} with chelating cation-anion Te II …I-Te IV contacts, to the six-membered chelate complex dppmSe2TeI2 with a square planar cis-Se2TeI2 group, and to dppeSe2TeI2 with trans-Se2TeI2 groups in a helical chain structure.