Te Bonds Research Articles

Reactivity of the metalloligand [Pt2(µ-S)2(PPh3)4] toward tellurium(II) thiourea complexes: synthesis and structural characterization of the ditellurium(I) derivative [{Pt2(µ-S)2(PPh3)4}2Te2]2+

Reaction of the platinum(II) sulfide metalloligand [Pt2(µ-S)2(PPh3)4] with the tellurium(II) source TeCl2(tu)2 (tu = thiourea) is dependent on reaction conditions employed. In the presence of added acid, the dominant species observed in the electrospray ionization (ESI) mass spectrum is the tetraplatinum species [{Pt2(µ-S)2(PPh3)4}2Te2]2+. This contains the Te22+ moiety and is related to the previously reported tellurium(I) dithiophosphinate analog [(Ph2PS2)2Te2]. However, in the absence of acid, considerable degradation of the {Pt2S2} metalloligand occurs as evidenced by the formation of the mononuclear complex [Pt{SC(NH2)NH}(PPh3)2]+ containing a deprotonated thiourea ligand, together with other thiourea-containing ions, identified by ESI MS. Likewise, attempted use of a fully substituted thiourea, viz. Me2NC(S)NMe2 (tmtu) in TeCl2(tmtu)2, also resulted in degradation of the {Pt2S2} core and detection of the known complex [(Ph3P)2PtCl{SC(NMe2)2}]+. The [{Pt2(µ-S)2(PPh3)4}2Te2]2+ cation was isolated with several anions, and unequivocal confirmation of the structure of the complex was obtained by an X-ray structure determination on the BF4- salt, which shows the presence of the Te22+ unit, with the Te–Te bond bridged by two {Pt2S2} metalloligands. Density functional theory was used to further probe the Te22+ bonding interactions in [{Pt2(μ-S)2(PPh3)4}2Te2]2+ and the previously reported [(Ph2PS2)2Te2].

Reaction of arylhydrazines with diaryl ditellurides in the air: Insight into bimolecular homolytic substitution on tellurium via Aryl–Te bond cleavage

AbstractThe reactivity of diaryl ditelluride and diaryl telluride toward aryl radicals was studied in detail. Diphenyl ditelluride underwent a bimolecular homolytic substitution (SH2) reaction with a phenyl radical generated from phenylhydrazine in the air, to afford diphenyl telluride in excellent yield. Based on this diphenyl telluride synthesis, a one‐pot synthesis of unsymmetrical diaryl tellurides was developed by the SH2 reaction of in situ generated diphenyl telluride with arylhydrazines in the air. The selectivity of mono‐/di‐substitution and the reactivity of arylhydrazines depend on the nature of the substituents on the arylhydrazines, that is, electron‐donating or ‐withdrawing group.

Energetics and Electronic Properties of Interstitial Chlorine in CdTe

The role of interstitial chlorine in the electronic properties of CdTe is addressed by density functional theory calculations including hybrid functionals and large unit cells. The stability and diffusion energy barriers of the impurity are analyzed as a function of the Fermi level position in the band gap. Chlorine is found to be stable in at least five interstitial sites with rather close formation energies, suggesting that they are all probable to be found. In p‐type CdTe, the most stable sites are at the center of a CdTe bond and at a split‐interstitial configuration, both acting as shallow donors. Whereas in n‐type CdTe, it is found at the tetrahedral site surrounded by Cd hosts, acting as a shallow acceptor. We also find that chlorine can induce a deep acceptor level in the bandgap after binding with three Cd host atoms, which can explain the experimentally observed high resistivity in Cl‐doped CdTe. The energy barriers for chlorine diffusion in both p‐type and n‐type CdTe are also discussed.

Second‐Order Nonlinear Optical Tensor Coefficients of LiXTe2 (X = Al, Ga, In) Chalcopyrite Semiconductors

AbstractUsing solid‐state theory of plasma oscillations, simple relations are proposed for the calculation of the second‐order nonlinear optical (NLO) tensor coefficients of LiXTe2 (X = Al, Ga, In) semiconductors. The values of bond lengths, energy gaps, dielectric constant, and NLO tensor coefficients of Li–Te and X–Te bonds and their total contribution to LiXTe2 compounds are calculated at zero frequency. The calculated results are in reasonable agreement with the known and reported results.

Syntheses and Structures of Zinc(tmeda)bis(aryltellurolato) and its Facile Chalcogenospecific Ligand Exchange Reactivity

Anaerobic treatment of Zn(tmeda)Br2, where tmeda denotes N,N,N′,N′‐tetramethylethylenediamine, with a solution of Na(TeAr), sodium aryltellurolate, in ethanol in a 1:2 stoichiometry led to the formation of highly air sensitive Zn(tmeda)(TeAr)2 (1–3), while a 1:1 stoichiometry afforded Zn(tmeda)Br(TeAr) (4). Crystallography revealed all complexes to be monomeric with four coordinate central zinc atoms bound to tmeda and two TeAr, or a TeAr and a Br ligand. Upon mixing two symmetrically substituted Zn(tmeda)(TeAr)2 complexes in solution, 125Te NMR revealed a facile ligand exchange providing Zn(tmeda)(TeAr)(TeAr′). In addition, Zn(tmeda)(TeAr)(TeAr′) complexes form on mixing symmetric Zn(tmeda)(TeAr)2 complexes and (TeAr′)2. The lability of the zinc complexes was put to advantage in ligand‐substitution reactions wherein treatment of SnCl4 with Zn(tmeda)(TeAr)2 affords Sn(TeAr)4 in excellent yields without the concurrent formation of the redox product (TeAr)2. The apparent lability of the Zn–Te bond prevented the volatilization of 1–3 for their use as chemical vapor deposition precursors for the fabrication of ZnTe thin films. On heating, to volatize the complexes, the complexes decompose to cubic ZnTe and TeAr2 sublimes from the samples. Thermal gravimetric analysis indicates the loss of tmeda followed by the loss of TeAr2.

Conformational trimorphism of bis(2,6-dimesitylphenyl)ditelluride

AbstractBesides the previously known α-form (monoclinic,P21/c, Z=4) of bis(2,6-dimesitylphenyl)ditelluride, two new polymorphic modifications, namely the β-form (monoclinic,P21/c, Z=8) and the γ-form (triclinic,P1̅, Z=2), were obtained serendipitously during chemical reactions. In all three modifications, the individual molecules possess significantly different conformations and bond parameters, such as Te–Te bond lengths, C–Te–Te bond angles, C–Te–Te–C torsion angles and intramolecular Menshutkin interactions, which is also reflected in their non-covalent interactions with adjacent molecules in the crystal lattice via London dispersion and electrostatic forces. The interplay between intermolecular and intramolecular forces in these conformational polymorphs was investigated using quantum chemical calculations, which reveal that the β-form should be thermodynamically stable at absolute zero. In contrast, crystallization experiments and thermoanalytical investigations indicate that the α-form is stable at high temperatures and therefore, both forms might be related by enantiotropism.

SiC‐Doped Ge2Sb2Te5 Phase‐Change Material: A Candidate for High‐Density Embedded Memory Application

AbstractPhase‐change memory is one of the most attractive solutions for embedded applications, thanks to the low cost of integration with current manufacturing processes and the good scaling behavior. Despite intensive research efforts that are devoted to the modification of Ge2Sb2Te5 (GST) phase‐change material, the obtained improvements are still unsatisfactory for high‐performance applications. In this paper, SiC‐modification is first introduced to enhance the amorphous stability of GST without sacrificing its transition speed. Several enhancements can be demonstrated, including better thermal stability (10‐year data retention above 120 °C), lower RESET voltage (about 3.0 V at 20 ns pulse width), reduced volume change (smaller than 3.0%), and expected operation cycles (more than 1.0 × 105). According to the findings, the local bonding nature of Ge/Te atoms can be tuned by C/Si dopants through forming CGe and SiTe bonds. Apart from strengthening the atomic binding network for desirable data retention, the element interdiffusion is also effectively controlled and suppressed. Together with finer grains, smaller density change, and more uniform morphology, the modified structure transition finally contributes to the reduced switching voltage and long‐term endurance. Hence, it is envisaged that SiC‐doped GST with such advantages will give a competitive option for high‐density and high‐performance embedded memory.

Spectroscopic properties and excited state dynamics of Sm3+ ions in zinc telluro-fluoroborate glasses

A new series of trivalent samarium doped B2O3–TeO2–ZnO–ZnF2–CaF2–BaF2 glasses were prepared and their spectroscopic behavior have been studied to understand the effect of Sm3+ ions concentration and to explore the local field effect on the symmetry around Sm3+ ions for the development of laser devices. Local structure and structural behavior are investigated through XRD, FTIR and Raman spectral measurements. The stretching vibrations of B‒O bond in BO3/BO4 units, Te–O stretching vibrations in TeO3/TeO4 units, and bending vibrations of B‒O‒B and Te‒O‒Te bonds were identified from FTIR and Raman spectral studies. Spectroscopic properties are investigated by recording optical absorption, excitation, luminescence and decay profiles. Judd-Ofelt (JO) theory has been implemented to get information about the local structure around Sm3+ ions in the chosen matrix using the experimental oscillator strength values obtained from the intensities of the absorption band transitions. Luminescence spectra of the Sm3+ ions doped present glasses were recorded by monitoring an excitation at 405 nm which exhibits 4G5/2→6HJ (J= 5/2, 7/2, 9/2 and 11/2) intra-4f transitions through an efficient energy transfer process. The luminescence quenching of Sm3+ ions emission were observed beyond 0.5 wt% of Sm3+ ion concentration which is mainly caused by the cross-relaxation process through various cross-relaxation channels and thus concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of the Sm3+ ions. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S= 6, which indicates that the nature of interaction takes place between Sm3+ ions for energy transfer through cross-relaxation is of dipole-dipole type.

Bond compressibility and bond Grüneisen parameters of CdTe

Extended x-ray absorption fine structure (EXAFS) at the Cd K edge and diffraction patterns have been measured on CdTe as a function of pressure from 100 kPa (1 bar) to 5 GPa using a cell with nano-polycrystalline diamond anvils and an x-ray focussing scanning spectrometer. Three phases—zincblende (ZB), mixed cinnabar-ZB and rocksalt (RS)—are well distinguished in different pressure intervals. The bond compressibility measured by EXAFS in the ZB phase is slightly smaller than the one measured by diffraction and decreases significantly faster when the pressure increases; the difference is attributed to the effect of relative vibrations perpendicular to the Cd–Te bond. The parallel mean square relative displacement (MSRD) decreases, the perpendicular MSRD increases when the pressure increases, leading to an increasing anisotropy of relative atomic vibrations. A constant-temperature bond Grüneisen parameter (GP) has been evaluated for the ZB phase and compared with the constant-pressure bond GP measured in a previous experiment; an attempt is made to connect the bond GPs measured by EXAFS and the more familiar thermodynamic GP and mode GPs; the comparisons suggest the inadequacy of the quasi-harmonic approximation to deal with the local vibrational properties sampled by EXAFS.

Inversion Symmetry Broken 2D 3R‐MoTe2

AbstractInversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well.

UV-Initiated Si–S, Si–Se, and Si–Te Bond Formation on Si(111): Coverage, Mechanism, and Electronics

Diaryl and dialkyl chalcogenide molecules serve as convenient precursors to silicon–chalcogenide bonds, ≡Si–E–R groups, on silicon surfaces, where E = S, Se, and Te. The 254 nm light, coupled with gentle heating to melt and liquefy the chalcogenide precursors for 15 min, enables formation of the resulting silicon–chalcogenide bonds. R groups analyzed comprise a long alkyl chain, octadecyl, and a phenyl group. Quantification of substitution levels of the silicon-hydride on the starting ≡Si(111)–H surface by an organochalcogen was determined by XPS, using the chalcogenide linker atom as the atomic label, where average substitution levels of ∼15% were found for all ≡Si–E–Ph groups. These measured substitution levels were found to agree with 2-dimensional stochastic simulations assuming kinetically irreversible silicon–chalcogen bond formation. Due to the small bond angle about the chalcogen atom, the phenyl rings in the case of ≡Si–E–Ph effectively block otherwise reactive Si–H bonds, leading to the observed...

Synthesis, thermal, structural and linear optical properties of new glasses within the TeO2-TiO2-WO3 system

The glass-forming domain and physical properties, namely, the density, thermal, structural and linear optical properties of new glasses within the TeO2-TiO2-WO3 system have been investigated. By means of micro-Raman spectroscopy, the structure of these glasses was examined based on a full-scale spectral decomposition. The optical transmission and refractive index dispersion were measured by UV–Vis-NIR spectroscopy and spectroscopic ellipsometry respectively. Consistent correlations were established between the structural and linear optical properties. Only minor structural modifications of the original TeO2-rich network are taking place upon adding TiO2 or WO3, suggesting the absence of Te–O–Te bond network depolymerization. Our results also suggest that, upon increasing TiO2 content, a phase separation occurs between amorphous TeO2-rich and amorphous TiO2-rich regions. We also argue that the structural trends upon adding WO3 evolve from uniformly dispersed WO6 octahedra (at low WO3 content) to amorphous WO3-like regions (at higher WO3 content) before the crystallization of γ-WO3 at 30 mol% of WO3. The compositional dependence of the refractive index and several optical constants (Urbach EU and dispersion Ed energies, oxide ion polarizabilities) is highlighted. These glasses collectively exhibit high refractive indices in the order of ~2.2.

Quasi-two-dimensional superconductivity from dimerization of atomically ordered AuTe2Se4/3 cubes

The emergent phenomena such as superconductivity and topological phase transitions can be observed in strict two-dimensional (2D) crystalline matters. Artificial interfaces and one atomic thickness layers are typical 2D materials of this kind. Although having 2D characters, most bulky layered compounds, however, do not possess these striking properties. Here, we report quasi-2D superconductivity in bulky AuTe2Se4/3, where the reduction in dimensionality is achieved through inducing the elongated covalent Te–Te bonds. The atomic-resolution images reveal that the Au, Te, and Se are atomically ordered in a cube, among which are Te–Te bonds of 3.18 and 3.28 Å. The superconductivity at 2.85 K is discovered, which is unraveled to be the quasi-2D nature owing to the Berezinsky–Kosterlitz–Thouless topological transition. The nesting of nearly parallel Fermi sheets could give rise to strong electron–phonon coupling. It is proposed that further depleting the thickness could result in more topologically-related phenomena.

Possible Mechanism for Hole Conductivity in Cu–As–Te Thermoelectric Glasses: A XANES and EXAFS Study

Recently synthesized thermoelectric Cu–As–Te glasses have been analyzed by X-ray absorption spectroscopy, both near-edge (XANES) and in the extended region (EXAFS), in order to shed light on the mechanism at the basis of the huge increase of conductivity, up to 5 orders of magnitude, that was found with Cu doping. Experimental data have been modeled by means of multiple-scattering calculations. Our model suggests that the experimental results can be interpreted in terms of a small charge-transfer from Te to Cu, leading to an unexpected positive valence for Te. Interestingly, on the basis of these findings, a global picture explaining the enhancement of electrical conductivity with Cu doping can be proposed: electrical conductivity is determined by the holes created in nonbonding Te 5p orbitals (lone pair) by Cu acceptors. The critical parameter to increase electrical conductivity is the number of Cu–Te bonds that are formed and not simply the number of Cu atoms.

Mechanical properties of thermoelectric lanthanum telluride from quantum mechanics

Lanthanum telluride (La3Te4) is an n-type high-performance thermoelectric material in the high temperature range, but its mechanical properties remain unknown. Since we want robust mechanical properties for their integration into industrial applications, we report here quantum mechanics (QM) simulations to determine the ideal strength and deformation mechanisms of La3Te4 under pure shear deformations. Among all plausible shear deformation paths, we find that shearing along the (0 0 1)/ slip system has the lowest ideal shear strength of 0.99 GPa, making it the most likely slip system to be activated under pressure. We find that the long range La–Te ionic interactions play the predominant role in resisting shear deformation. To enhance the mechanical strength, we suggest improving the long ionic La–Te bond stiffness to strengthen the ionic La–Te framework in La3Te4 by a defect-engineering strategy, such as partial substitution of La by Ce or Pr having isotypic crystal structures. This work provides the fundamental information to understand the intrinsic mechanics of La3Te4.

Reaction with organic halides as a general method for the covalent functionalization of nanosheets of 2D chalcogenides and related materials

Abstract

From Mixed-Valent Phenyltellurenyl Bromide Ph(Br2)TeTePh to the Isolation of [{(C6H5)Te}19O24Br5]Br4

The σ-donor ligand selone L (L = 1,3-dibutylbenzimidazolin-2-selone, C15H22N2Se) caused cleavage of the Te–Te bond of the mixed-valent phenyltellurenyl bromide {Ph(Br2)TeTePh} in THF to produce the selone adduct of a phenyltellurenyl cation with phenyltellurium dibromide anion, [PhTe(L)][PhTeBr2] (1). The adduct disproportionated in polar solvent (CH3CN), followed by hydrolysis with traces of water to give the largest telluroxane cluster, [{(C6H5)Te}19O24Br5]Br4, with a Te19O24 skeleton. The bowl-shaped telluroxane cluster dimerizes in the solid state, forming the molecular capsule {[{(C6H5)Te}19O24Br5]Br4}2. The cluster is amphipathic and has a hydrophilic cavity consisting of tellurium, oxygen, and bromide atoms, which contains 24H2O molecules.

Local structural characteristics of Sb2Te3 films studied by reverse Monte Carlo modeling

Atomic configuration and connectivity of Sb2Te3 thin film are investigated using high-energy X-ray diffraction and reverse Monte Carlo simulation. Atomic model details of Sb2Te3 thin film are compared with liquid and amorphous Sb2Te3 reported in other article. Simulations show that both Sb–Sb and Te–Te homopolar bonds are present in the models. In phase transition process, atomic configuration of the sample rearranges gradually through the forming of Sb–Te bonds and the breaking of Sb–Sb and Te–Te bonds.

Variations of Local Motifs around Ge Atoms in Amorphous GeTe Ultrathin Films

Phase-change materials, the highly promising candidate for nonvolatile data recording, present a different phase-change property when film thickness shrinks to very deep submicron scale. The local structure of amorphous GeTe ultrathin films, which contributes to the characteristics of phase change, is examined using X-ray absorption measurements. Ge atoms are found to be low-coordinated when the film thickness decreases. Ge atoms are linked to neighbor atoms by covalent bond, and the weaker Ge–Te bonds are more easily broken, which suggests that Ge atoms are located in the defective Ge2Te3 local arrangement. The mixture of sp3/sp2 hybridization and 3-coordinated Ge found in ab initio molecular dynamics simulations also supports this local motif. The exponential rise of crystallization temperatures of ultrathin films with decreasing film thickness, which is a vital parameter for phase change process, can be well explained by the proposed defective GeTe local arrangement.

Superconductivity Bordering Rashba Type Topological Transition

Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.