Effect of in and Zn additives on some thermal properties of a-Se

In the present work, the effect of In and Zn on some thermo–physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of amorphous Se (a-Se) have been studied. For this, simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) are used at room temperature for twin pellets of Se, Se₉₀In₁₀ and Se₉₀Zn₁₀ alloys using transient plane source (TPS) technique. It has been found that In and Zn additives changes significantly the values of thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of a-Se studied in the present work. The results have been analyzed in terms of average bond strength and effective molecular weight of the binary alloys.     

Thermoelectric properties of Cu-doped n-type (Bi2Te3)0.9–(Bi2−xCuxSe3)0.1(x=0–0.2) alloys

n-Type (Bi₂Te₃)_0.9–(Bi_2−xCu_xSe₃)_0.1 (x=0–0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu_2.86Te₂ precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x0.1) can reduce the lattice thermal conductivity (κ_L), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi₂Se_0.3Te_2.7 (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies.     

Effect of indium additive on thermal transport properties of Se–Te–Cd multi-component chalcogenide glasses

The thermal conductivity, thermal diffusivity and specific heat per unit volume of twin pellets of Se₇₅Te_15?Cx Cd₁₀In _x (x?=?0, 5, 10 and 15) glasses, were carried out at room temperature by transient plane source technique. Results indicated that both values of thermal conductivity (??) and thermal diffusivity (??) are varied with In (indium) content and highest for 5?at.% of In, whereas the specific heat per unit volume is almost constant with increase of indium concentration. This shows that Se₇₅Te₁₀Cd₁₀In₅ glass can be considered as a critical composition at which the alloy becomes chemically ordered and most thermally stable than other compositions. This compositional dependence behaviour of thermal conductivity and thermal diffusivity can explained in terms of iono-covalent type bond which In makes with Se and Te as it is incorporated in Se?CTe?CCd glasses.     

Thermoelectric properties of Ag-doped n-type (Bi2Te3)0.9-(Bi2−xAgxSe3)0.1 (x=0-0.4) alloys prepared by spark plasma sintering

Ag-doped n-type (Bi₂Te₃)_0.9-(Bi_2−xAg_xSe₃)_0.1 (x=0-0.4) alloys were prepared by spark plasma sintering and their physical properties evaluated. When at low Ag content (x=0.05), the temperature dependence of the lattice thermal conductivity follows the trend of (Bi₂Te₃)_0.9-(Bi₂Se₃)_0.1; while at higher Ag content, a relatively rapid reduction above 400 K can be observed due possibly to the enhancement of scattering of phonons by the increased defects. The Seebeck coefficient increases with Ag content, with some loss of electrical conductivity, but the maximum dimensionless figure of merit ZT can be obtained to be 0.86 for the alloy with x=0.4 at 505 K, about 0.2 higher than that of the alloy (Bi₂Te₃)_0.9-(Bi₂Se₃)_0.1 without Ag-doping.     

Effect of some metallic additives (Ag, Cd, and Sn) on thermal transport properties of a-Se

In this study, we have studied the effect of elements Ag, Cd, and Sn as chemical modifiers on some thermal transport properties (thermal conductivity, diffusivity, and specific heat per unit volume) of amorphous Se. Concurrent measurements of thermal transport properties such as effective thermal conductivity (??_e), thermal diffusivity (??_e), and specific heat per unit volume (??C _v) are used at room temperature for twin pellets of pure Se- and Se-based binary Se₉₈M₂ (M?=?Ag, Cd, and Sn) alloys using transient plane source technique. We have also determined the thermal inertia I _T using the experimental values of thermal conductivity and specific heat per unit volume for present amorphous alloys. The increasing sequence of measured thermal transport properties is also discussed.     

Interactions and glass formation in the TlAs2Se4-Tl3As2Se3Te3 system

The TlAs₂Se₄-Tl₃As₂Se₃Te₃ system was studied using differential thermal analysis (DTA), powder X-ray diffraction, microstructure observation, and microhardness and density measurements. A phase diagram of the title system was constructed. This system is a quasi-binary join of the TlSe-As₂Se₃-As₂Te₃ quasi-ternary system. All alloys of the system under standard conditions are prepared in the glassy form. The system has a eutectic, which contains 50 mol % Tl₃As₂Se₃Te₃ and melts at 150°C. The TlAs₂Se₄-base solid solution in the system extends to 12 mol % Tl₃As₂Se₃Te₃, and Tl₃As₂Se₃Te₃-based solid solution extends to 20 mol % TlAs₂Se₄.     

New tantalum polychalcogenides with infinite anionic chains: K12Ta6Se35 and KTaTe3

The new compounds K₁₂Ta₆Se₃₅ and KTaTe₃ have been synthesized through the reaction of Ta metal with a K₂Q_n(Q = Se, Te) flux. K₁₂Ta₆Se₃₅, crystallizes with 4 formula units in space group Pbcn of the orthorhombic system in a cell of dimensions a = 8.3390(17) Å, b = 13.259(3) Å, c = 56.023(11) Å (t = −120 °C). KTaTe₃ crystallizes with 20 formula units (or 4 formula units of K₅Ta₅Te₁₅) in the monoclinic space group P2₁/c in a cell of dimension a = 7.7177(15) Å, b= 13.826(3) Å, c = 30.981(6) Å, and β = 90.11(3)° (t = −120 °C). Each structure consists of infinite anionic chains of Ta-containing polyhedra well separated by K⁺ cations. In K₁₂Ta₆Se₃₅ there are Ta₂Se₁₁ units formed by the face sharing of two TaSe₇ elongated bipyramids. These Ta₂Se₁₁ units are in turn interconnected by Se₂ and Se₃ units to form _α¹[Ta₆Se₃Se₃₅¹²⁻]infinite chains. In KTaTe₃, the _α¹[TaTe₃⁻] infinite chains arise from the face sharing of distorted TaTe₆ octahedra.     

Transport Properties of Bi2−xInxSe3 Single Crystals

The paper reports on the temperature dependence of the electrical and thermal conductivity, Hall constant, and Seebeck coefficient of Bi_2−xIn_xSe₃ (x=0, 0.2, 0.4) single crystals measured over the temperature range from 2 to 300 K. One single-valley conduction band model is used to interpret relations among transport coefficients. The data analysis relies on the use of a mixed carrier scattering mechanism consisting of acoustic scattering and scattering on ionized impurities. The effect of In incorporation into the Bi₂Se₃ crystal lattice on the individual components of thermal conductivity is evaluated and discussed.     

Transport and optical properties of heavily hole-doped semiconductors BaCu2Se2 and BaCu2Te2

Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu₂Se₂ and BaCu₂Te₂ are reported. Experimental data include the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for , and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2×10¹⁸ and 5×10¹⁹ cm⁻³ near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm² V⁻¹ s⁻¹ for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu₂Se₂, while no similar feature was observed for BaCu₂Te₂. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented.     

Syntheses and Structures of the Quaternary Copper Tellurides K3Ln4Cu5Te10 (Ln=Sm, Gd, Er), Rb3Ln4Cu5Te10 (Ln=Nd, Gd), and Cs3Gd4Cu5Te10

Six quaternary alkali-metal rare-earth copper tellurides K₃Ln₄Cu₅Te₁₀ (Ln=Sm, Gd, Er), Rb₃Ln₄Cu₅Te₁₀ (Ln=Nd, Gd), and Cs₃Gd₄Cu₅Te₁₀ have been synthesized at 1123 K with the use of reactive fluxes of alkali-metal halides ACl (A=K, Rb, Cs). All crystallographic data were collected at 153 K. These compounds crystallize in space group Pnnm of the orthorhombic system with two formula units in cells of dimensions (A₃Ln₄, a, b, c (Å)): K₃Sm₄, 16.590(2), 17.877(2), 4.3516(5); K₃Gd₄, 16.552(4), 17.767(4), 4.3294(9); K₃Er₄, 16.460(4), 17.550(4), 4.2926(9); Rb₃Nd₄, 17.356(1), 17.820(1), 4.3811(3); Rb₃Gd₄, 17.201(2), 17.586(2), 4.3429(6); Cs₃Gd₄, 17.512(1), 17.764(1), 4.3697(3). The corresponding R₁ indices for the refined structures are 0.0346, 0.0315, 0.0212, 0.0268, 0.0289, and 0.0411. The three K₃Ln₄Cu₅Te₁₀ structures belong to one structure type and the Rb₃Ln₄Cu₅Te₁₀ (Ln=Nd, Gd) and Cs₃Gd₄Cu₅Te₁₀ structures belong to another one, the difference being the location of one of the three unique Cu atoms. Both structure types are three-dimensional tunnel structures that contain similar Ln/Te fragments built from LnTe₆ octahedra and CuTe₄ tetrahedra. The CuTe₄ tetrahedra form ¹_∞[CuTe⁵⁻₃] and ¹_∞[CuTe³⁻₂] chains. The alkali-metal atoms, which are in the tunnels, are coordinated to seven or eight Te atoms.     

La3Pd4Zn4 and La3Pt4Zn4 with a different coloring of the Gd3Cu4Ge4-type structure

Abstract  

The intermetallic zinc compounds La₃Pd₄Zn₄ and La₃Pt₄Zn₄ were synthesized by induction melting of the elements in sealed tantalum tubes. The structures were refined from X-ray single-crystal diffractometer data: Gd₃Cu₄Ge₄ type, Immm, a = 1,440.7(5), b = 743.6(2), c = 419.5(2) pm, wR ₂ = 0.0511, 353 F ² for La₃Pd₄Zn₄; and a = 1,439.9(2), b = 748.1(1), c = 415.66(6) pm, wR ₂ = 0.0558, 471 F ² for La₃Pt₄Zn₄ with 23 variables per refinement. The palladium (platinum) and zinc atoms build up a three-dimensional polyanionic [Pd₄Zn₄] (260–281 pm Pd–Zn) and [Pt₄Zn₄] (260–279 pm Pt–Zn) network in which the lanthanum atoms fill cavities of CN 14 (6 Pd/Pt + 8 Zn for La1) and CN 12 (6 Pd/Pt + 6 Zn for La2), respectively. The copper position of the Gd₃Cu₄Ge₄ type is occupied by zinc and the two crystallographically independent germanium sites by palladium (platinum), a new coloring pattern for this structure type. Within the [Pd₄Zn₄] and [Pt₄Zn₄] the Pd2 and Pt2 atoms form Pd2–Pd2 (291 pm) and Pt2–Pt2 (296 pm) dumbbells. The structures of La₃Pd₄Zn₄ and La₃Pt₄Zn₄ are discussed with respect to the prototype Gd₃Cu₄Ge₄ and the Zintl phase Sr₃Li₄Sb₄. Temperature-dependent magnetic susceptibility measurements indicate diamagnetism for La₃Pt₄Zn₄ and Pauli paramagnetism for La₃Pd₄Zn₄.     

Effect of Bi incorporation on the glass transition kinetics of Se<Subscript>85</Subscript>Te<Subscript>15</Subscript> glassy alloy

Bulk samples of Se_85-xTe₁₅Bi_x glassy alloys are obtained by melt quenching technique. Differential scanning calorimetry has been applied to determine the thermal properties of Se-rich Se_85-xTe₁₅Bix glassy alloys at different heating rates. The glass transition temperature (T _g) is found to shift to a higher temperature with increasing heating rate and with Bi addition. Activation energy and fragility of the system is also calculated. Specific heat is evaluated and a jump in heat capacity is observed at T _g. Theoretical parameters viz; density, molar volume, number of atoms per unit volume, lone pair electrons and cohesive energy of the system are also reported.     

Structure and properties of Ce3Pd3Bi4, CePdBi, and CePd2Zn3

The intermetallic cerium compounds Ce₃-Pd₃Bi₄, CePdBi, and CePd₂Zn₃ were synthesized from the elements in sealed tantalum ampoules in an induction furnace. The compounds were characterized by X-ray powder and single crystal diffraction: CeCo₃B₂ type (ordered version of CaCu₅), P6/mmm, a = 538.4(4), c = 427.7(4) pm, wR2 = 0.0540, 115 F ² values, 9 variables for CePd₂Zn₃ and Y₃Au₃Sb₄ type, I [`4]{\bar 4} 3d, a = 1005.2(2) pm, w R2 = 0.0402, 264 F ² values, 9 variables for Ce₃Pd₃Bi₄, and MgAgAs type, a = 681.8(1) pm for CePdBi. The bismuthide structures are build up from three-dimensional networks of corner-sharing PdBi₄ tetrahedra with Pd–Bi distances of 281 (Ce₃Pd₃Bi₄) and 296 pm (CePdBi), respectively. The cerium atoms are located in larger voids of coordination number 12 (Ce₃Pd₃Bi₄) and 10 (CePdBi). In CePd₂Zn₃ the cerium atoms fill larger channels within the three-dimensional [Pd₂Zn₃] network with 18 (6 Pd + 12 Zn) nearest neighbors. The three compounds contain stable trivalent cerium with experimental magnetic moments of μ_eff = 2.70(2), 2.48(1), and 2.49(1) μ_B/Ce atom for CePd₂Zn₃, Ce₃Pd₃Bi₄, and CePdBi, respectively. Susceptibility and specific heat data gave no hint for magnetic ordering down to 2.1 K.     

Synchrotron-radiation photoemission study of the V–VI layered compounds Bi2Te3, Bi2Se3, Sb2 Te3 and Sb2Te2Se

The valence band (VB) density of states and the binding energies of the weakly bound core levels have been measured by XUV photoelectron spectroscopy using synchrotron radiation for four V–VI layered compounds. Chemical shifts of the core levels are determined which support the partial ionicity of the bonds involved. The chemical shifts of the emission from two unequivalent crystal sites were shown to differ by less than 30 meV for the compounds Bi₂Te₃, Bi₂Se₃ and Sb₂Te₃.VB and core-level photoemission spectra for the V–VI compounds Bi₂Te₃, Bi₂Se₃, Sb₂Te₃ and Se₂Te₂Se have been presented. Chemical shifts of the Te 4d, Bi 5d, Sb 4d and Se 3d levels were determined, indicating partial ionicity of the mainly covalent bonds involved. Chemical-shift differences originating from atoms at two different crystal sites are <30 meV. In a simple model this implies that similar charge transfers do occur even though completely different bond orbitals were proposed for the and the AB⁽²⁾ bonds. Finally, the fact that no surface core-level shifts were observed tends to confirm the very weak influence of the van der Waals-like bonds on the B⁽²⁾ atoms.     

Syntheses, crystal structures and optical properties of the first strontium selenium(IV) and tellurium(IV) oxychlorides: Sr3(SeO3)(Se2O5)Cl2 and Sr4(Te3O8)Cl4

Two new quaternary strontium selenium(IV) and tellurium(IV) oxychlorides, namely, Sr₃(SeO₃)(Se₂O₅)Cl₂ and Sr₄(Te₃O₈)Cl₄, have been prepared by solid-state reaction. Sr₃(SeO₃)(Se₂O₅)Cl₂ features a three-dimensional (3D) network structure constructed from strontium(II) interconnected by Cl⁻, SeO₃²⁻ as well as Se₂O₅²⁻ anions. The structure of Sr₄(Te₃O₈)Cl₄ features a 3D network in which the strontium tellurium oxide slabs are interconnected by bridging Cl⁻ anions. The diffuse reflectance spectrum measurements and results of the electronic band structure calculations indicate that both compounds are wide band-gap semiconductors.     

Etude structurale de seleniures,tellurures et selenio-tellurures de titane Ti3Se4−xTex (0 ⩽ x ⩽ 4)

The compounds Ti₃Se_4?xTe_x are prepared. Their structure closely depends upon thermal conditions of synthesis. Treatments at 600°C and quenching give pure monoclinic compounds isotypic with Ti₃Se₄ and Ti₃Te₄ in narrow ranges of composition (x ? 0.5 and x ? 3.5). At 800°C, polycrystalline pure products are obtained with an hexagonal B8 unit cell (a′, ?') when x ? 3. At 1000°C, for x ? 3.5, almost pure compounds crystallize with that same hexagonal unit cell; an orthorhombic lattice is observed for x = 4.Moreover, twinning is observed on single crystals obtained after quenching from 800 or 1000°C, with x = 1, 2, 3 and 4. These crystals seem to exhibit an hexagonal unit cell (2a′, 2?'), but in fact their lattice is orthorhombic or monoclinic with a real I unit cell: a ≈ a′√3, b ≈ a′, c ≈ 2c′. The explanation of the phenomenon allows us to correct some misinterpretations found in the literature on “TiTe” single crystals.     

Synthesis and characterization of quaternary selenides Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15

Quaternary selenides Sn₂Pb₅Bi₄Se₁₃ and Sn_8.65Pb_0.35Bi₄Se₁₅ were synthesized from the elements in sealed silica tubes; their crystal structures were determined by single-crystal and powder X-ray diffraction. Both compounds crystallize in monoclinic space group C2/m (No.12), with lattice parameters of Sn₂Pb₅Bi₄Se₁₃: a = 14.001(6) Å, b = 4.234(2) Å, c = 23.471(8) Å, V = 1376.2(1) Å³, R₁/wR₂ = 0.0584/0.1477, and GOF = 1.023; Sn_8.65Pb_0.35Bi₄Se₁₅: a = 13.872(3) Å, b = 4.2021(8) (4) Å, c = 26.855(5) Å, V = 1557.1(5) Å³, R₁/wR₂ = 0.0506/0.1227, and GOF = 1.425. These compounds exhibit tropochemical cell-twinning of NaCl-type structures with lillianite homologous series L(4, 5) and L(4, 7) for Sn₂Pb₅Bi₄Se₁₃ and Sn_8.65Pb_0.35Bi₄Se₁₅, respectively. Measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps; Sn₂Pb₅Bi₄Se₁₃ is n-type, whereas Sn_8.65Pb_0.35Bi₄Se₁₅ is a p-type semiconductor with Seebeck coefficients −80(5) and 178(7) μV/K at 300 K, respectively.     

The structure Tl3SbS3, Tl3SbSe3, Tl3SbS3−xSex, and Tl3SbyAs1−ySe3

The space group symmetry and crystal structure of Tl₃SbS_3−xSe_x compounds in the composition range 0 < x < 3 have been determined by a combination of powder X-ray diffraction, electron diffraction, and high-resolution electron microscopy. The incongruently melting compound Tl₃SbSe₃ has been shown to crystallize in cubic space group P2₁3 with a = 9.435Å in a structure related to that of Langbeinite. The convergent beam electron diffraction pattern of Tl₃SbS₃ is in accord with the space group R3m determined by X-ray diffraction. The cubic Langbeinite-type structure is found for Tl₃SbS_3−xSe_x for 0.5 < x < 3 and for Tl₃Sb_yAs_1−ySe₃ for 0.077 < y < 1.0. A five-component compound Tl₃Sb_0.5As_0.5Se_1.5S_1.5 was also found to be cubic.     

Crystal structure of a barium-zinc decametaphosphate Ba2Zn3P10O30

Barium-zinc decametaphosphate, Ba₂Zn₃P₁₀O₃₀, is monoclinic, $\text{P2}\text{n}$, with the unit cell parameters a = 21.738(15), b = 5.356(5), c = 10.748(8) Å, β = 99.65(3)° and Z = 2. The crystal structure was solved with a final R value of 0.041. This salt provides the first structural evidence for the existence of a 10-phosphorus ring anion.     

Structure and properties of triclinic Ni0.85Mo6Te8

The structure of Ni_0.85Mo₆Te₈ was refined from single-crystal X-ray diffraction data at room temperature. It is triclinic, space group

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; 1619 reflections, 75 refined parameters, R = 0.031. The Mo atoms form distorted octahedral clusters (2.69 Å ≤ d_intra[Mo---Mo] ≤ 2.81 Å; 3.58 Å < d_inter[Mo---Mo]). The Ni atoms are disordered (site occupancy: 0.423(7); d[Ni---Ni] = 2.586(6) Å), and interact strongly with one Mo₆ cluster (d[Ni---Mo] = 2.603(3) and 2.958(3) Å), and weakly with another (d[Ni---Mo] = 2.985(3) Å). The structure transforms at 1057(5) K into a rhombohedral modification (a_hex = 10.457(2) Å, c_hex = 11.866(3) Å at 1073 K). Measurements on powders suggest metallic conductivity (5.1 × 10⁻⁴ Ω-cm at 293 K) and weakly temperature-dependent paramagnetism (110 × 10⁻⁶ emu/g at 100 K).