Mechanochemical preparation of palladium chalcogenides

Palladium chalcogenides of PdS, Pd₁₇Se₁₅, PdSe₂, PdTe, Pd₃Te₂ and PdSeTe were prepared by milling elemental mixtures, using a planetary-type ball mill at room temperature. These chalcogenides were obtained within 30 min. Pd₁₇Se₁₅ was also obtained when the elemental mixture was immersed in methanol or ethanol at room temperature for 10 days.     

Solid-state reactions to synthesize nanostructured lead selenide semiconductor powders by high-energy milling

Both solid-solid and gas-solid reactions have been traced during high-energy milling of Se and PbO powders under vial (P, T) conditions in order to synthesize the PbSe phase. Chemical and thermodynamic arguments are postulated to discern the high-energy milling mechanism to transform PbO-Se micropowders onto PbSe-nanocrystals. A set of reactions were evaluated at around room temperature. Therefore an experimental campaign was designed to test the nature of reactions in the PbO-Se system during high-energy milling.     

Pressure effects on the phonon modes in beryllium chalcogenides

We report first-principles calculations of the structural, lattice-dynamical and dielectric properties for zinc-blend beryllium chalcogenides: BeS, BeSe, and BeTe. The ground state properties, such as the lattice structure and bulk modulus, are calculated using a plane wave pseudopotential method within the density functional theory. A linear response approach is employed in order to derive the high-frequency dielectric constants, Born effective charges and phonon frequencies. Furthermore, the pressure dependence of phonon modes is also detailed.     

Electronic structure of the filled tetrahedral compound LiCdP and zinc–blende InP: Application of the interstitial insertion rule

We report on first principles studies of the electronic properties of the filled tetrahedral compound LiCdP and zinc–blende InP, using the full potential linearized augmented plane wave method within the local density approximation. The total energy calculations show that the α phase (Li⁺ near the anion) to be more stable than the β one (Li⁺ near the cation) for the LiCdP. The conduction band valleys follow the Γ–L–X ordering of increasing energy for β-LiCdP and InP, and the Γ–X–L one for α–LiCdP. The conduction band modifications are discussed and found to obey the interstitial insertion rule except for the Γ state of β-LiCdP. The valence charge density analysis shows that the Cd–P bond is covalent whereas the Li–P and the Li–Cd ones in α and β phases, respectively, are ionic.     

Sonochemical synthesis of nanocrystalline lead chalcogenides: PbE (E = S, Se, Te)

Nanocrystalline lead chalcogenides PbE (E=S, Se, Te) were synthesized conveniently by the reaction of Pb(CH₃COO)₂·3H₂O and elemental chalcogens in ethylenediamine (en) under ultrasonic irradiation. XRD and TEM techniques were employed to characterize the products. The solubility of chalcogen in en was found to be the key factor of the reaction. A three-step mechanism was proposed to account for the formation of the products.     

Structural and electronic properties of CdTe:Cl from first-principles

The structural and electronic properties of the dominant intrinsic defect of the Cd vacancy (V_Cd) and the Cl impurity in CdTe are studied using density functional theory. V_Cd is calculated to be a shallow double acceptor. Cl will substitute Te site (Cl_Te) and then act as a shallow donor in CdTe. Moreover, Cl_Te can bond with V_Cd, forming the defect complexes of Cl_Te–V_Cd. Cl_Te−V_Cd is a shallower acceptor than that of V_Cd. The defect complexes of (Cl_Te−V_Cd)⁻¹ can improve the p-doping behavior of CdTe.     

First-principles study of structural stabilities,elastic and electronic properties of transition metal monocarbides (TMCs) and mononitrides (TMNs)

The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B8₁) and the tungsten carbides (B_h) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θ_D) and sound velocities (v_m) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B8₁), ReN – (B8₁), WN – (B8₁) and OsC – (B8₁) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements.     

Structural and electronic properties of AlX (X = P,As, Sb) nanowires: Ab initio study

Present paper discusses the structural stability and electronic properties of AlX (X = P, As and Sb) nanowires in its linear, zigzag, ladder, square and hexagonal type atomic configurations. The structural optimization has been performed in self consistence manner by using generalized gradient approximation with revised Perdew, Burke and Ernzerhof type parameterization. The study observes that in all the three nanowires, the square shaped atomic configuration is the most stable one. The calculated electronic band structures and density of states profile confirms the semiconducting behaviour of linear and zigzag shaped nanowires of AlP, whereas for AlAs and AlSb nanowires are metallic. The ground state properties have also been analysed in terms of bond length, bulk modulus and pressure derivative for all the nanowires along with their bulk counterpart. The lower bulk modulus of all the linear shaped geometries of AlX nanowires in comparison to its bulk counterpart indicates softening of the material at reduced dimension.     

High-pressure synthesis of a new calcium thioborate, CaB2S4

A new calcium thioborate, CaB₂S₄, was synthesized at high-pressure/temperature condition of 6.2 GPa and 800-1100 °C. The crystal structure was refined by the Rietveld method using powder X-ray diffraction data. The compound crystallizes into a cubic unit cell (a=11.210 Å, space group: Pa3), isostructural with a high-pressure polymorph of calcium borate, CaB₂O₄-IV. The unit cell consists of three-dimensional linkage of BS₄-tetrahedra, and calcium atoms have coordination number of 12.     

Raman studies of selenium nanowires under high pressure

The selenium nanowires with diameter of 70 nm and length of 40 μm were synthesized by a facile solution method. High-pressure behavior of Se nanowires has been investigated by in situ Raman scattering up to 20.2 GPa at room temperature. A reversible phase transition from hexagonal to monoclinic occurs at 18.1 GPa. This transition pressure is higher than that of 14.0 GPa for bulk Se. The intrinsic geometry and/or the increasing energy band gap of Se nanowires are considered to contribute to the increase of transition pressure.     

Composite crystal Sr8/7TiSy with y = 2.84-2.97

Sr_8/7TiS_y (y=2.84-2.97) has been prepared by controlling the partial pressure of sulfur. The XRD and the ED patterns could not be indexed because of incommensurate structures; they were, therefore, indexed by four-dimensional formalism with simple lattice parameters of A, C_Ti and C_Sr in a hexagonal setting. However, a commensurate structure was obtained at y=2.84 in Sr_8/7TiS_y, the XRD and ED patterns of which were indexed by three- and four-dimensional formalisms. The sulfides, including incommensurate and commensurate structures, could be regarded as a single phase with a homogeneity range of sulfur of y=2.84-2.97, when the four-dimensional formalism was used. On the other hand, from the viewpoint of three-dimensional formalism, the structure contains two penetrating hexagonal subcells. The lattice parameter “a” in hexagonal setting is common to both subcells, while c is given by c=pC_Ti=qC_Sr, where p and q are integers, and C_Ti and C_Sr are the periodicities in c-direction of the two subcells, respectively. Hence, there is an infinite number of the structures in the composition range of y=2.84-2.97 in Sr_8/7TiS_y.     

Synthesis of monodispersed CdSe nanocrystals in poly(styrene-alt-maleic anhydride) at room temperature

Nanocomposite of CdSe/poly(styrene-alt-maleic anhydride) (PSM) was successfully prepared via an in situ reaction process at room temperature and ambient pressure. Transmission electron microscopy (TEM) analysis revealed that CdSe nanoparticles with a small size and narrow size distribution were obtained. The obtained nanocomposite was also characterized by FT-IR, XRD, ultraviolet-visible, and fluorescence spectroscopy.     

Ab initio study of antisite defective layered Ge2Sb2Te5

By means of ab initio calculations, we have investigated the antisite defects in layered Ge₂Sb₂Te₅ (GST). Our results show that both Te_Sb and Sb_Te antisite defective GST alloys are energetically favorable and mechanically stable. Furthermore, the presence of antisite defects results in the decrease in band gaps and hence the increase in the electrical conductivity, while shows slight effect on chemical bonding characters. Based on the present results, increased electrical conductivity and decreased thermal conductivity are expected by introducing antisite defects in GST related layered materials.     

Elastic constants and high pressure structural transitions in yttrium pnictides

We present first-principles calculations on the structural, elastic and high pressure properties of yttrium pnictide compounds, using the pseudo-potential plane-waves approach based on density functional theory, within the generalized gradient approximation. Results are given for lattice constant, bulk modulus and its pressure derivative. The pressure transition at which these compounds undergo structural phase transition from NaCl-type (B1) to CsCl-type (B2) structure is calculated and compared with previous calculations and available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio of the B1 phase for YN, YP, YAs and YSb compounds. We estimated the Debye temperature of these compounds from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of YN, YP, YAs and YSb compounds, and it still awaits experimental confirmation.     

Study of thermal and optical properties of GeS2-Ga2S3-Ag2S chalcogenide glasses

Chalcogenide glasses in the GeS₂-Ga₂S₃-Ag₂S pseudo-ternary system were prepared by melt-quenching technique. The structural evolvement of the glasses was studied by Raman spectroscopy. The Raman results show that the addition of Ag₂S involves the breaking of [S₃Ge-GeS₃] ethane-like units and the formation of Ag-S ionic bonds. The results of differential scanning calorimetry (DSC) show that the glasses have relatively high-glass transition temperatures and good thermal stabilities. These GeS₂-Ga₂S₃-Ag₂S glasses have a wide range of transmission approximately from 0.50 to 12.5 μm. In addition, with the method of Maker fringe, SHG was observed in the 0.9GeS₂-0.05Ga₂S₃-0.05Ag₂S glass irradiated by an electron beam. The value of second-order nonlinear optical susceptibility d is as large as 6.6 pm/V, and the poling mechanism of electron beam irradiation was also discussed in this work.     

Influence of thermal conditions on the combustion synthesis of Si2N2O phase

This work is a contribution to the study of Si₂N₂O synthesis via Self-Propagating High-temperature Synthesis (SHS).The elaboration of Si₂N₂O was carried out using two kinds of experimental equipments and differences both in reaction temperatures and in products compositions were evidenced.In order to determine the reaction mechanisms, several compositions and thermal conditions of the reactant mixture were studied.Considering our results, two kinds of reaction mechanisms for the combustion synthesis of Si₂N₂O could be suggested. Furthermore, the results previously reported in the literature have been explained in the light of this work.The SHS samples were characterized by X-ray diffraction and scanning electron microscopy (SEM) analysis. Their quantitative compositions were determined by Rietveld refinement.     

Synthesis of β-Si3N4 whiskers by SHS

This paper presents the results of SHS of β-Si₃N₄ whiskers from silicon powders with α-Si₃N₄ as diluents under high nitrogen pressure. The effect of the addition of different amounts of Y₂O₃ on β-Si₃N₄ whisker synthesis has been investigated in detail. The results revealed that Y₂O₃ additive had a marked effect on the growth of β-Si₃N₄ whiskers compared that without additives. The optimum amount of Y₂O₃ addition is from 2.4 to 4.8 wt.%.     

Thermal and optical properties of the Ga-Ge-Sb-Se glasses

A selected glass composition from the Ga-Ge-Sb-Se has been studied in detail for potential applications in the 8-12 μm region. The Ga₅Sb₁₀Ge₂₅Se₆₀ glass has a high enough glass transition temperature (283 °C), a relatively high refractive index (2.63 at 10 μm) and is very stable towards crystallization. An original purification method is developed to produce high purity glass with good transmission up to 15 μm. This glass is very resistant in normal environmental conditions and even in hot water (60 °C) during 24 h. It may be a good candidate for producing infrared components operating in the mid and far infrared region.     

Double-dentate solvent-directed growth of multi-armed CdS nanorod-based semiconductors

The multi-armed CdS architectures can be synthesized from the reaction of the anhydrous CdCl₂ and sulfur powders in ethylenediamine, in which a simple one-step reactant–solvent synchronous (RSS) co-assisted effect was proposed to be responsible to the growth of the multi-armed structures. The as-prepared products were characterized by XRD, XPS and TEM. In addition, their optical properties were also shown by UV–vis and fluorescence spectrum. FT-IR spectrum indicated that the dissociation of ethylenediamine molecule absorbed on the surface of CdS resulted in the formation of intermediate CdS(en)_m−n cores and thus provided the condition for the anisotropy growth of CdS. The present technique may give a clue to grow the one-dimensional nano-sized semiconductors by the proper choice of the reactant and the solvent.     

The synthesis and characterization of nanocrystalline Cu- and Ag-based multinary sulfide semiconductors

The novel polygonal flake like Ag₈SnS₆ crystal, Cu₂FeSnS₄ flaky, and well-dispersed Cu₂CoSnS₄ nanoparticles were successfully prepared via a convenient hydrothermal reaction route at relatively low temperature, which was avoiding the use of high temperature treatments or toxic organic solvents. The products were characterized by means of X-ray powder diffraction (XRD), transmission electronic microscopy (TEM), X-ray photoelectronic spectra (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). It was found that the reaction temperature played a key role for the formation of the target products.