Sb Bonds Research Articles

HfSb2–xTex: The Second New Compound on the Quasi‐Binary Section HfSb2‐HfTe2 with Different Sb–Sb Interactions

AbstractThus far, three different ribbons and layers of antimony atoms with various Sb–Sb bonds were found in Hf5Sb9, HfSb2 and HfSbTe. We uncovered a new variant when trying to dope Hf5Sb9 with tellurium atoms, namely HfSb2–xTex, with 0.4 ≤ x ≤ 0.7. HfSb2–xTex adopts the monoclinic OsGe2 type, space group C2/m, a = 10.5216(8) Å, b = 3.7142(3) Å, c = 8.5924(7) Å, β = 11.571(1), V = 292.05(4) Å3 (Z = 4) when x = 0.5. This structure is composed of a layer of puckered six‐membered rings of antimony atoms, with Sb–Sb distances of 2.82 and 3.12 Å. The different antimony atom substructures are compared in this article. Independent of the exact Sb/Te ratio, monoclinic HfSb2–xTex is predicted to be metallic, as are Hf5Sb9, HfSb2 and orthorhombic HfSbTe.

Thermal characterization of Se85−xSb15Snx (10≤x≤13) chalcogenide glasses

Results of crystallization kinetics, viscosity, specific heat, thermal stability, and glass forming ability of Se85−xSb15Snx (x=10, 11, 12.5, and 13) chalcogenide glasses, using differential scanning calorimeter (DSC), under non-isothermal condition have been reported and discussed. The variation of the peak temperature of crystallization Tp with the heating rate β has been used to investigate the growth kinetics using Kissinger, Takhor, and Augis–Bennet models. The activation energy of crystallization Ec has been found to increase with Sn content and the crystal growth occurs in one dimension. The increasing trend of Ec is interpreted in terms of enhancement of the degree of cross-linking due to the formation of SnSe4/2 structural units of energies higher than that of Se–Se and Se–Sb bond energies. The viscosity η against 1/T curves has also been drawn and indicated that the atoms of ternary Se–Sb–Sn glasses required more energy, with the addition of Sn, to complete the transformation from amorphous to crystalline state. The demand for thermal stability has been ensured through the calculations of the enthalpy released ΔHc during the crystallization process and S-parameter, while the obtained values of the reduced glass transition temperature Trg and Hurby number HR have been used to estimate the glass forming ability (GFA). Results reveal that, both thermal stability and GFA enhanced with increasing Sn content and the studied samples were prepared from strong glass-forming liquids. The obtained values for the specific heat difference ΔCp, between the equilibrium liquid and the glass, have been found to decrease with increasing Sn content and are in support of the results of thermal stability and GFA.

Phase stability, bonding and electrical conduction of amorphous carbon-added Sb films

A study of the phase stability, chemical bonding and mechanisms of electrical conduction of carbon-added amorphous Sb films was carried out. Addition of carbon, which results in the formation of C–Sb bonds, hinders long-range Sb–Sb ordering. This leads to enhanced thermal stability of amorphous Sb film. The crystallization temperature of Sb–C films with 0, 8 and 13 at.% C are ∼25, 256 and 262 °C, respectively. The electrical conductivity of Sb92C8 film is p-type, showing an increase of more than 4 orders of magnitude in carrier concentration upon crystallization corresponding to the observed resistance drop.

Glass transition kinetics and optical band gap in Se 85− xSb 15Sn x ( x = 10, 11, 12.5, and 13) chalcogenide glasses

Se 85− x Sb 15Sn x (10 ≤ x ≤ 13) chalcogenide glasses were prepared by melt quenching technique. The glass transition temperature T g of the samples was recorded at different heating rates using differential scanning calorimeter DSC. From the heating rate dependence of T g, the activation energy for thermal relaxation E t was calculated using Moynihan model and Kissinger equation. It is found that T g increases with Sn content due to enhancement of both the degree of cross-linking parameter D cl and the mean bond energy of the average cross-linking per atom 〈 E cl〉. The observed increase in D cl and 〈 E cl〉 is attributed to the formation of SnSe 4/2 structural units of energies higher than that of Se–Se and Se–Sb bond energies. The decreasing trend of E t with the addition of Sn is an indication of improving thermal stability as it is also evident from the values of the temperature difference T c − T g. Correlation of T g values with the physical parameters of the studied glasses (for instance, the average coordination number 〈 Z〉, the average heat of atomization ( H s), the overall mean bond energy 〈 E〉, and the optical band gap ( E g)) reveals that T g increases linearly with 〈 Z〉, H s, and 〈 E〉 but the behavior with E g is opposite.

Electronic properties of [formula omitted] solid solution investigated by density-functional theory

We present density-functional theory (DFT) calculations on the electronic structures of Zn1−xCdxSb solid solution for x=0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0. The electronic band structures, energy gaps, Bader’s charges, and electron localization functions were calculated. We show that the energy gaps and Bader’s charges exhibit peculiar behaviour for the x=0.5 alloy, which agrees with previously reported data. The plot of the electron localization functions shows that the Sb–Zn and Sb–Cd bonds are ionic in nature while the Sb–Sb bonds are covalent.

Lattice dynamical origin of peak thermoelectric performance in AgPbmSbTe2+m observed by inelastic neutron scattering

Phonon densities of states (DOS) for the high performing thermoelectric material, AgPbmSbTe2+m (LAST-m, m = 16, 18, and 20), were extracted from time-of-flight inelastic neutron scattering measurements. The phonon DOS of LAST-18 differs remarkably from LAST-16 and LAST-20 by exhibiting a dramatic broadening of its acoustic modes that increases on heating. This broadening coincides with a minimum in the thermal conductivity, a maximum in the electrical conductivity and Seebeck coefficient, and a related peak in thermoelectric performance. We argue that the anomalous broadening originates with scattering enhanced by modifications to Te-Ag(Sb) bonds caused by their resonant electronic states falling near the Fermi energy for m = 18.

Role of surface structural motifs on the stability and reflectance anisotropy spectra of Sb-rich GaSb(001) reconstructions

The structure of the technologically important---but still mostly unknown---GaSb(001)--$c(2\ifmmode\times\else\texttimes\fi{}6)$ surface reconstruction is investigated by means of ab initio simulations of reflectance anisotropy spectroscopy (RAS) and total energy calculations. A large number of reconstruction models for the GaSb(001) surface in the Sb-rich coverage regime are considered. The influence of each single surface structural motif on the RAS spectra is studied in detail, as well as their role in the surface stability with regard to application of the electron counting rule (ECR). We interpret the features of the RAS data measured for this reconstruction and suggest a new model for the $c(2\ifmmode\times\else\texttimes\fi{}6)$ phase. In this model a few Sb atoms in the second layer are randomly substituted by Ga, forming surface antisite defects. When used to fulfill the ECR, this ``doping'' effect considerably lowers the total energy of the long chain $c(2\ifmmode\times\else\texttimes\fi{}6)$ reconstruction model, making it competitive with the more stable short-chain $(4\ifmmode\times\else\texttimes\fi{}3)$ reconstructions. Formation of the surface antisites occurs spontaneously in the presence of dynamical negative charge fluctuations and is favored by the excellent matching between GaSb(001) and metallic Sb and by the natural softness of the Ga--Sb bonds. Calculations of the reflectance anisotropy spectra confirm that this structure is a major component of a largely disordered surface, where motifs of the stable $(4\ifmmode\times\else\texttimes\fi{}3)$ reconstructions are also present.

Adjunctive use of an anti-oxidant agent to improve resistance of hybrid layers to degradation

Objective To determine the role of an anti-oxidant agent (ascorbic acid-AA) on resin–dentin bonds resistance to degradation of two adhesives. Methods Flat dentin surfaces from 48 human molars were bonded as per manufacturer's instructions with: a two-step etch-and-rinse self-priming adhesive (Single Bond-SB) and a two-step self-etch adhesive (Clearfil SE Bond-CSE). Half of the specimens were bonded with the same adhesives, but after the addition of 10% AA into their formulation. Resin composite build-ups were constructed incrementally and sectioned into resin–dentin beams (1.0 mm 2) that were stored under four conditions: (1) water immersion for 24 h; (2) water immersion for 1 year; (3) water immersion for 4 years; and (4) chemical challenging (immersion in 10% NaOCl for 5 h). Beams were pulled to failure in tension at 0.5 mm/min. Mean microtensile bond strength (MTBS) data were analysed with ANOVA and multiple comparisons tests ( P < 0.05). Analysis of debonded dentin beams was performed by scanning electron microscopy (SEM). Results After 24 h, SB and CSE performed equally, regardless of AA incorporation. Inclusion of AA on CSE formulation decreased MTBS following one-year water storage, but maintained SB bond strength values even after four years of water storage. NaOCl challenge diminished MTBS for both adhesives, but when AA was added to SB, this reduction was significantly lower. Conclusions The inclusion of AA on adhesive's formulation exerts a protective role on resin–dentin bonds resistance to degradation when SB is used. Bonding durability of CSE may be compromised by the addition of sodium ascorbate.

Effect of Bonding Characteristics on the Instability of GexSb1 − x Films

Phase change characteristics in films with various compositions (, , and ) were investigated. A change in crystalline structure indicated that the phase separation occurred at temperatures that exceeded the phase transition temperatures of the films, and this change was dependant on the composition of . The extended X-ray absorption fine structure data showed a change in the bond coordination of Ge from fourfold to threefold during the phase transition. Moreover, the phase separation of Ge occurred gradually with increasing temperature, due to the weak Ge–Sb bonds in the crystalline state. The Raman spectroscopy data showed a suppressed Peierls distortion caused by the Ge–Sb bonds in the crystalline state. The presence of weak Ge–Sb bonds results in instability of the films, resulting in an irreversible transition.

Optical Properties of GaSb Nanofibers.

Amorphous GaSb nanofibers were obtained by ion beam irradiation of bulk GaSb single-crystal wafers, resulting in fibers with diameters of ~20 nm. The Raman spectra and photoluminescence (PL) of the ion irradiation-induced nanofibers before and after annealing were studied. Results show that the Raman intensity of the GaSb LO phonon mode decreased after ion beam irradiation as a result of the formation of the amorphous nanofibers. A new mode is observed at ~155 cm-1 both from the unannealed and annealed GaSb nanofiber samples related to the A1g mode of Sb–Sb bond vibration. Room temperature PL measurements of the annealed nanofibers present a wide feature band at ~1.4–1.6 eV. The room temperature PL properties of the irradiated samples presents a large blue shift compared to bulk GaSb. Annealed nanofibers and annealed nanofibers with Au nanodots present two different PL peaks (400 and 540 nm), both of which may originate from Ga or O vacancies in GaO. The enhanced PL and new band characteristics in nanostructured GaSb suggest that the nanostructured fibers may have unique applications in optoelectronic devices.

Photo induced optical changes in Sb/As 2S 3 multilayered film and (As 2S 3) 0.93Sb 0.07 film of equal thickness

The increase in optical band gap (photo bleaching) due to light illumination was studied at room temperature as well as at low (4.2 K) temperature for Sb/As 2S 3 multilayered film of 640 nm thickness by Fourier Transform Infrared Technique. The interdiffusion of Sb into As 2S 3 matrix results the formation of Sb–As 2S 3 ternary solid solutions which is explained by the change in optical band gap ( E g), absorption coefficient ( α), Tauc parameter ( B 1/2), Urbach edge ( E e). At the same time, photo darkening phenomena was observed in (As 2S 3) 0.93Sb 0.07 film of same thickness both at low and room temperatures. From our X-ray Photoelectron Spectroscopy measurements, we are able to show that some of the As–As, S–S and Sb–Sb bonds are converted into As–S and S–Sb bonds in case of multilayers. We found that the energetically favoured heteropolar bond formation take place by a phonon-assisted mechanism using the lone pair π electrons of S 2 0. But in case of (As 2S 3) 0.93Sb 0.07 film, the homopolar bonds are playing a major role.

Surface- and edge-states in ultrathin Bi–Sb films

Employing first-principles calculations, we studied the electronic structure of ultrathin Bi–Sb films, focusing on the appearance of surface or edge states that are topologically protected. Our calculations show that in ordered structures the Bi–Sb bonds are quite strong, forming well-defined double layers that contain both elements. We find surface states appearing on the (111) surface of a thin film of layerwise ordered Bi–Sb compound, while thin films in (110) orientation are insulating. In the gap of this insulator, edge states can be found in a (110)-oriented ribbon in the A17 (black phosphorus) structure. While these states are strongly spin polarized, their topological properties are found to be trivial. In all structures, we investigate the influence of spin–orbit coupling and analyze spin polarization of the states at the boundaries of the material.

Filler-reduced phonon conductivity of thermoelectric skutterudites: Ab initio calculations and molecular dynamics simulations

The phonon conductivities of CoSb 3 and its Ba-filled structure Ba x (CoSb 3) 4 are investigated using first-principle calculations and molecular dynamics (MD) simulations, along with the Green–Kubo theory. The effects of fillers on the reduction of the phonon conductivity of filled skutterudites are then explored. It is found that the coupling between filler and host is strong, with minor anharmonicity. The phonon density of states and its dispersion are significantly influenced by filler-induced softening of the host bonds (especially the short Sb–Sb bonds). Lattice dynamics and MD simulations show that, without a change in the host interatomic potentials, the filler–host bonding alone cannot lead to significant alteration of acoustic phonons or lowering of phonon conductivity. The observed smaller phonon conductivity of partially filled skutterudites is explained by treating it as a solid solution of the empty and fully filled structures.

Controlled fabrication of oriented co-doped ZnO clustered nanoassemblies

Clustered nanoassemblies of Mn doped ZnO and co-doped ZnO (Mn, Sn co-doped ZnO; Mn, Sb co-doped ZnO; and Mn, Bi co-doped ZnO) were prepared by refluxing their respective precursors in diethylene glycol medium. The co-doping elements, Sn, Sb and Bi exist in multi oxidation states by forming Zn–O–M (M = Sb, Bi and Sn) bonds in hexagonal wurtzite nanostructure. The analyses of detailed structural characterization performed by XRD, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), show that co-doping ions are successfully incorporated into the ZnO nanostructure and do not appear as precipitates or secondary phases. HRTEM analysis also confirmed the oriented attachment of nanocrystals as well as their defect structures. The formation/activation of higher amount of intrinsic host defects, for instance, oxygen vacancies in co-doped ZnO as compared to Mn doped ZnO sample is evident from Raman spectra. The doped and co-doped samples exhibit ferromagnetic like behavior at room temperature presumably due to the presence of defects. Specifically, it has been observed that the incorporation of dopant and co-dopants into ZnO structure can modulate the local electronic structure due to the formation/activation of defects and hence, cause significant changes in their structural, vibrational, optical and magnetic properties.

Atomic structure of amorphous and crystallized Ge15Sb85

Ge 15 Sb 85 is a promising material for phase-change memory applications owing to its very short crystallization times. As deposited amorphous samples of sputter deposited Ge15Sb85 have been investigated by extended x-ray absorption fine structure (EXAFS) measurements on both, Sb and Ge K absorption edges. After crystallizing the specimen, x-ray diffraction (XRD) and EXAFS measurements have been performed to analyze the atomic structure at different annealing conditions. Thus, experimental techniques focusing on the long range order as well as on the local order have been combined. Sb atoms have on average 3.2(2) nearest neighbors, while Ge atoms have 4.0(3). The Ge–Ge and Ge–Sb bond lengths are determined to 2.46(2) and 2.66(1) Å, respectively and agree well with those observed in the amorphous phase of the common phase-change material Ge2Sb2Te5. After crystallizing the sample at 250 °C, very different EXAFS spectra with modified Ge–Sb bond lengths are observed. The higher concentration of Ge neighbors at the Ge edge as compared to the as-deposited sample is indicative for phase separation. For the corresponding sample, XRD does not show reflections of Ge, which indicates that the agglomeration of Ge is amorphous or below the coherence length of the x-radiation. The EXAFS spectrum shows a superposition of two phases: one with bond lengths which agree with sp3-hybridized Ge [2.43(1) Å] and another one with longer Ge–Ge bond lengths [2.79(8) Å]. This result can be explained by phase separation in the material.

Effects of water-storage on the physical and ultramorphological features of adhesives and primer/adhesive mixtures

The aims of this study were to evaluate the ultimate tensile strength (UTS) and elastic modulus (E) of adhesives, and primer/adhesive mixtures after aging for 6 months in water or oil; and to compare silver uptake patterns under the TEM. A one-step self-etching adhesive (One-up Bond F: OB), two two-step self-etching primers (SE Bond: SE and Protect Bond: CP), and two etch-and-rinse systems (Single Bond: SB and Prime&Bond NT: PB) were used. Bonding and primer solutions of self-etching systems were also mixed (SE+P and CP+P). Most adhesives presented decreased UTS after water-storage. Similar or increased UTS was observed after oil storage. Except for SB, E values did not change after water-storage, but they increased after storage in oil. OB, CP+P and SE+P presented more silver uptake. The effects of water-storage were material-dependent, and significantly affected the mechanical properties and silver uptake patterns of adhesives.

Local atomic and electronic structures of equiatomic liquid alloy KSb from 923 to 1773K

Abstract The local atomic and electronic structures of equiatomic liquid alloy KSb have been investigated using ab initio molecular dynamics simulations. There is a small peak located at about 62° in the covalent Sb Sb bond-angle distribution function. The height of 62° peak increases with temperature. The further analysis show that this peak attributes to the triangular structures with each Sb atom covalently bonded to the other two in the liquid KSb and their number increases with temperature. Therefore, there exist isolated Sb atoms, covalently bonded Sb dimers, triangles with three covalent Sb Sb bonds and short covalently bonded Sb chains in the liquid KSb. Upon temperature increasing the covalent Sb chains tend to break into short pieces so that the isolated Sb atoms, covalently bonded Sb dimers and triangles with three covalent Sb Sb bonds increase in numbers. The obtained total electronic densities of states at different temperatures give a reasonable explanation of the electronic conductivity increasing with temperature.

Nanoscale Phase Separation and Building Blocks of Ge2Sb2Te5N and Ge2Sb2Te5N2 Thin Films

The atomic structures of thin films of nitrogen-doped Ge2Sb2Te5 (GST) rapid phase-change memory materials with the general compositions Ge2Sb2Te5N (10% N-GST) and Ge2Sb2Te5N2 (18% N-GST) have been investigated by reverse Monte Carlo refinement based on experimental electron diffraction reduced density functions and density functional theory molecular dynamics simulations. It was found that the nitrogen dopant forms predominantly Ge−N bonds, resulting from nanoscale germanium nitride phase separation during cooling. As in the case of pure GST, the main building blocks of the structure are squares of Ge(Sb)−Te−Sb(Ge)−Te atoms with the contribution from rings containing homopolar Sb−Sb, Te−Te, and Ge−Sb bonds increasing with the nitrogen doping level. These squares are related to the elementary building blocks of the corresponding crystalline structures of the metastable cubic phase of GST. The persistent fragments of the germanium nitride phase are azadigermiridine type N−Ge−Ge−N four-membered rings, with central Ge−Ge bonds. There is an indication from theoretical simulations that two amorphous phases may be present in 18% N-GST, with different bonding types.

Ab initio study of structural, electronic, and elastic properties of M2SbP (M = Ti, Zr, and Hf)

This study predicts the structural behaviour of selected M2SbP compounds with the same structure as MAX phases. Zero pressure results of the lattice parameters, equilibrium volume, and the internal parameter ZM are calculated with an error less than 3%. Band structure, total and partial density of states were calculated and show the metallic character of these phases. Moreover we observed strong hybridising states; M d–P p, and M d–Sb p. The pressure dependence of the volume, and the lattice parameters were studied. The stiffness of M–P, and M–Sb bonds was discussed in term of relative length change under hydrostatic pressure. Hf2SbP present the highest bulk modulus and the unidirectional elastic modulus C33 is slightly greater than C11.

Syntheses, structures and properties of the pnictide oxides R2PnO 2 ( R = Ce, Pr; Pn = Sb, Bi)

Compounds with the chemical formula R 2 PnO 2 ( R = Ce, Pr and Pn = Sb, Bi) were prepared by reactions between adequate amounts of Ce 2O 3 (Pr 4O 7), Pn and RPn in sealed tantalum ampoules at 1770 K. Both bismuth compounds crystallize in the anti-ThCr 2Si 2 type of structure ( I4/ mmm, tI10). In the case of R 2SbO 2 a (4 × 4 × 1) super cell of the anti-ThCr 2Si 2 structure type is observed. Compared with the basis structure, the antimony atoms are displaced from the ideal positions forming Sb Sb bonds perpendicular to the c-axis. The magnetic susceptibility measurements indicate that the rare earth metals are in the trivalent state, and the electrical conductivity measurements show semiconducting behavior for R 2SbO 2 and metallic conductivity for R 2BiO 2, respectively. Both, the Sb Sb bond formation in the semiconducting antimonides, and the metallic conductivity of the bismuthides are in accordance with the description as [ R 3+] 2[ Pn 2−][O 2−] 2.