Ag2SeGa2Se3 pseudobinary phase diagram

The pseudobinary Ag₂Se-Ga₂Se₃ phase diagram has been redetermined by differential thermal analysis, x-ray diffraction, and crystal growth studies. A new ternary phase, Ag₉GaSe₆, has been observed, and the phase boundaries of the solid solutions based on AgGaSe₂ and Ga₂Se₃ have been measured. The optical scattering observed in slow-cooled crystals of AgGaSe₂ is due to precipitates of a Ga₂Se₃-based solid solution, which has the approximate composition AgGa₇Se₁₁. The new Ag₂Se-Ga₂Se₃ diagram differs significantly from the one given by Palatnik and Belova but is qualitatively similar to the Ag₂S-Ga₂S₃ diagram recently reported by Brandt and Krämer.     

Preparation of ultra-long Sb2Se3 nanoribbons via a short-time solvothermal process

Large-scale antimony selenide (Sb₂Se₃) nanoribbons with uniform size have been prepared by solvothermal method using antimony chloride (SbCl₃), tartaric acid (C₄H₆O₆) and selenium metal powder (Se) as raw materials, N, N-dimethylformamide (DMF) as the solvent at 180 °C for 4 h. The powder X-ray diffraction (XRD) pattern shows the Sb₂Se₃ crystals belong to the orthorhombic phase with calculated lattice constants a = 1.159, b = 1.172 and c = 0.3978 nm. The quantification of EDS analysis peaks gives an atomic ratio of 2:3 for Sb:Se. Transmission electron microscopic (TEM) studies reveal the appearance of as-prepared Sb₂Se₃ is ribbon-like with the typical width of ca. 20 nm. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of Sb₂Se₃ nanoribbons is proposed.     

Phase relations in the ternary system Cu-In-Se

The phase relations of the ternary system Cu-In-Se were studied at 750° C by quenching experiments. Special attention was given to the region CuInSe₂In₂Se₃-In₄Se₃. Only four ternary phases with extended homogeneity ranges were found to exist. They were characterized by X-ray powder diffraction, electron microprobe analysis (EK8PA)' end optical microscopy. Differential thermal analysis (DTA) investigations allowed us to construct theT-x diagram of the Cu₂Se-In₂Se₃. out between 47 and 100 mol% In₂Se₃. Besides, it was also possible to give a tentative diagram of the solid-liquid equilibria at 750° C and to get some information on the sub-solid existence fields beside the Cu₂Se-In₂Se₃ cut.     

A physicochemical study of the Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

We have studied phase relations in the Sb₂Se₃–Nd₂Se₃ system and mapped out its T–x phase diagram using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The system contains one compound, with the composition NdSbSe₃, which melts incongruently at 865 K and crystallizes in orthorhombic symmetry with the following lattice parameters: а = 12.77(1) Å, b = 14.08(1) Å, and c = 5.82(5) Å (Z = 8, ρ_meas = 6.20 g/cm³, ρ_x = 6.38 g/cm³). At room temperature, the Nd₂Se₃ solubility in Sb₂Se₃ is 5 mol % and the Sb₂Se₃ solubility in Nd₂Se₃ is 2.5 mol %. The Sb₂Se₃–Nd₂Se₃ system has a eutectic located at 15 mol % Nd₂Se₃, with a melting point at 755 K. The electrical conductivity and thermoelectric power of the (Sb₂Se₃)_1–x (Nd₂Se₃) _x solid solutions have been measured as functions of temperature.     

Phase diagram and thermoelectric properties of Ag3−x Sb1+x Te4 system

In order to obtain better thermoelectric performance in the composition domain should be stabilized, the phase diagram of the Ag_3–x Sb_1+x Te₄ system by varying the Ag:Sb ratio. The phase diagram is investigated using the differential thermal analysis and the powder X-ray diffraction techniques. The Seebeck coefficient and the electrical resistivity of the grown bulk crystals of the system are also measured. The phase diagram of the Ag_3–x Sb_1+x Te₄ system indicates that a mixed phase of AgSbTe₂ and Ag₂Te, which is expected to show higher thermoelectric performance, exists in a wide temperature range between 600 and 830 K at a composition of Ag_2.2Sb_1.8Te₄. The maximum of Seebeck coefficient for AgSbTe₂ (x = 1) is 0.73 mV/K at about 680 K. The thermoelectric performance is lowered by the compositional deviation from Ag:Sb:Te = 1:1:2.     

Investigation of Sb<Subscript>65</Subscript>Se<Subscript>35</Subscript>/Sb multilayer thin films for high speed and high thermal stability application in phase change memory

Sb₆₅Se₃₅/Sb multilayer composite thin films were prepared by depositing the Sb₆₅Se₃₅ and Sb layers alternately. In situ resistance vs. temperature was measured and the crystallization temperature increased with thickening the Sb₆₅Se₃₅ layer in Sb₆₅Se₃₅/Sb thin films. The data retention temperature of 10 years increased greatly from 14 °C of pure Sb to 103 °C of [Sb₆₅Se₃₅(3 nm)/Sb(7 nm)]₃. Also, the band gap was broadened and the surface became smoother. X-ray diffraction patterns for the studied materials revealed that Sb and Sb₂Se₃ phases coexisted in Sb₆₅Se₃₅/Sb thin films. Absorbing the advantages of the fast phase change for Sb, the [Sb₆₅Se₃₅(1 nm)/Sb(9 nm)]₅ multilayer thin film had an ultrafast amorphization speed of 1.6 ns. The results indicated that Sb₆₅Se₃₅/Sb multilayer thin film was a potential phase change material for fast speed and good stability.     

One-step electrodeposited CuInSe2 thin films studied by Raman spectroscopy

CuInSe₂ thin films one-step electrodeposited under different conditions were studied by MicroRaman spectroscopy to identify and quantify the individual phases present in the films.From the analysis of the Raman spectra, the main ternary phase (CuInSe₂) and elementary selenium Se⁰ were clearly identified. Specific chemical etches confirm the presence of elementary selenium Se⁰ and copper selenide binary phases Cu_xSe in selenium rich film.The amounts of these two phases were evaluated from X-ray Fluorescence measurements and confirmed using phase selective chemical treatments.     

Single step electrochemical synthesis of Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films: effect of molarities of precursor solution

In the present investigation, we have successfully synthesized polycrystalline Sb₂Se₃ thin films by single-step electrochemical method. Effect of concentration of precursor solution on structural, morphological, optical, and wettability properties by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption, and contact angle measurement have been investigated. It is evident from XRD pattern that Sb₂Se₃ thin films are polycrystalline having orthorhombic crystal structure. Also, as precursor concentration increases the diffraction peak intensity also increases. Scanning electron micrographs reveal that the increase in precursor concentration causes the formation of soap foam like microstructure which is spread in the form of ellipsoids over whole substrate surface. The optical band gap decreases from 1.49 to 1.35 eV and contact angle decreases from 40° to 13°, i.e., the surface of Sb₂Se₃ thin films converts from hydrophilic to superhydrophilic nature due to increase in precursor concentration. In addition, the holographic interferometric properties have been studied. The thickness, stress to substrate and deposited mass of the thin films is determined using double exposure holographic interferometry (DEHI) technique.     

Epitaxial growth of topological insulator Bi2Se3 film on Si(111) with atomically sharp interface

Atomically sharp epitaxial growth of Bi₂Se₃ films is achieved on Si(111) substrate with molecular beam epitaxy. Two-step growth process is found to be a key to achieve interfacial-layer-free epitaxial Bi₂Se₃ films on Si substrates. With a single-step high temperature growth, second phase clusters are formed at an early stage. On the other hand, with low temperature growth, the film tends to be disordered even in the absence of a second phase. With a low temperature initial growth followed by a high temperature growth, second-phase-free atomically sharp interface is obtained between Bi₂Se₃ and Si substrate, as verified by reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and X-ray diffraction. The lattice constant of Bi₂Se₃ is observed to relax to its bulk value during the first quintuple layer according to RHEED analysis, implying the absence of strain from the substrate. TEM shows a fully epitaxial structure of Bi₂Se₃ film down to the first quintuple layer without any second phase or an amorphous layer.     

Synthesis and Optical Properties of CuInSe2 Films

The growth of CuInSe₂ films via evaporation from a compound source is studied by x-ray diffraction and x-ray fluorescence analysis. It is shown that, on heating, CuInSe₂ dissociates into copper and indium selenides, which partially vaporize before film deposition. At the beginning of the deposition process, the source consists mainly of Cu₂Se, CuInSe₂, and In₂Se₃ in different ratios, depending on the source temperature. During deposition, two phases vaporize for the most part: CuInSe₂ and In₂Se₃ or Cu₂Se and CuInSe₂, depending on the source temperature. As a result, some of the selenium, a highly volatile component, is lost, and the grown films consist of Cu₂Se _x (x 1), Se-deficient CuInSe₂, and InSe. At a source temperature of 1040°C, the impurity phases vaporize at approximately equal rates, and the grown films consist of CuInSe₂ only. During continuous heating of the source, all the decomposition products are transferred to the substrate, and the film is very close in composition to the source. The chemical composition and structure of the films are determined, and their optical absorption spectra are measured near the fundamental edge at 290 K. The absorption data are used to evaluate the band-structure parameters of CuInSe₂. A technique is proposed for assessing the band structure of this compound.     

Glass formation in the GeSe2 (As2Se3)–Sb2Se3–CdTe systems

Glass-forming regions in GeSe₂–Sb₂Se₃–CdTe (I) and As₂Se₃–Sb₂Se₃–CdTe (II) systems have been determined by visual, X-ray diffraction and electron microscope analyses. Glasses have been obtained in the GeSe₂-rich region in system I and As₂Se₃-rich region in system II, respectively. Glassformation has been observed along the tie-lines GeSe₂–Sb₂Se₃-line (30–100 mol% GeSe₂) and As₂Se₃–CdTe-line (45–100 mol% As₂Se₃). In the binary GeSe₂–CdTe and As₂Se₃–CdTe systems, glasses has found homogeneous in the concentration ranges 0–5 mol% CdTe (I) and 0–7 mol% CdTe (II), respectively. Up to 15 mol% CdTe are dissolved in the system GeSe₂–Sb₂Se₃ and in the system As₂Se₃–Sb₂Se₃, up to 12 mol% CdTe are dissolved. The basic physical–chemical characteristics of the glasses are investigated—density, microhardness, transformation temperature, crystallization temperature, melting temperature. A compositional dependence of these properties is shown. IR spectra of the samples are investigated.     

Preparation and characterization of belt-like Sb2Se3 crystals

Orthorhombic Sb₂Se₃ belts are synthesized via a hydrothermal treatment at 200 °C and pH = 9-10 for 16 h. Transmission electron microscopic (TEM) images show that as-obtained Sb₂Se₃ belts are with a typical width in the range of 200-400 nm and length up to 20 μm. High-resolution transmission electron microscopic (HRTEM) studies reveal that the Sb₂Se₃ are oriented in the [001] growth direction. The influences of poly vinyl alcohol (PVA) and the reaction conditions on the formation of belt-like Sb₂Se₃ microstructures are discussed.     

Thermal analysis and annealing temperature dependence of electrical properties in Sn<Subscript>10</Subscript>Sb<Subscript>20</Subscript>Se<Subscript>70</Subscript> glassy semiconductor

The melt-quenched Sn₁₀Sb₂₀Se₇₀ sample in the bulk form was used to prepare films on well-cleaned glass substrates by thermal evaporation method. The activation energy for glass transition (apparent) and crystallization has been analyzed by using the Kissinger formulation. The X-ray diffraction study shows the crystallization of Sb₂Se₃ phase in the major proportion as compared to the SnSe₂ phase. The SEM images film of the show the appearance of spherical globules upon annealing below the glass transition temperature. The effect of annealing temperature on the electrical and optical properties has been studied. A linear fit between ΔE and E _o is observed, indicating the validity of Meyer–Neldel rule with the change in the annealing temperature.     

Phase equilibria in the systems AgInSe<Subscript>2</Subscript>-HgIn<Subscript>2</Subscript>Se<Subscript>4</Subscript> and AgInSe<Subscript>2</Subscript>-HgSe

The equilibrium phase diagrams along the AgInSe₂-HgIn₂Se₄ and AgInSe₂-HgSe joins of the ternary system Ag₂Se-HgSe-In₂Se₃ have been constructed using X-ray diffraction and differential thermal analysis. Both joins are pseudobinary, with eutectic phase diagrams (type V in Roseboom’s classification). The eutectics are located at ≃30 mol % HgIn₂Se₄ (melting point of 1000 K) and ≃54 mol % HgSe (993 K), respectively. Both systems have considerable terminal solid-solution ranges.     

Thermoelectric materials based on Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions with optimal performance in the range 100–400 K

We have optimized the compositions of thermoelectric materials based on Sb₂Te₃-Bi₂Te₃ solid solutions using Czochralski-grown single crystals. The thermoelectric performance of Sb₂Te₃-Bi₂Te₃ solid solutions containing 0–100 mol % Bi₂Te₃ and Bi₂Te₃-Sb₂Te₃-Bi₂-Bi₂Se₃ solid solutions containing 2, 4, or 7 mol % Bi₂Se₃ has been investigated. The Bi₂Se₃-doped crystals are found to have higher thermoelectric figures of merit compared to the undoped crystals. The optimal crystal compositions are selected for different temperatures in the range 100–400 K.     

Kinetics and mechanism of the isothermal bulk crystallization of As<Subscript>2</Subscript>Se<Subscript>3</Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> ≤ 0.55) glasses

The kinetics and mechanism of stepwise transformations underlying the isothermal bulk crystallization of As₂Se₃Sn _x (x = 0.26, 0.40, 0.55) semiconductor glasses in the temperature range 210–310°C have been studied using ¹¹⁹Sn Mössbauer spectroscopy, X-ray diffraction, density and electrical conductivity measurements, and microhardness tests. The results demonstrate that small particles of the primary phase SnSe initiate heterogeneous nucleation and two-dimensional growth of crystals of the secondary, major phase As₂Se₃.     

Properties of SnO2-based ceramics

Some SnO₂-based ceramics of the ternary and binary systems SnO₂-Sb₂O₃-CuO have been prepared and some of their properties have been measured. It was observed that most of their properties, which include density, porosity, d.c. electrical conductivity, as well as the crystal occurrence, were dependent on the presence of CuO. Crystal phase occurrence was investigated using the X-ray diffraction technique and it was found that the phases were predominantly SnO₂ and Sb₂O₄ crystals. The d.c. conductivity at different sintering temperatures was found to be enhanced by the simultaneous presence of Sb₂O₃ and CuO.     

Preparation of rod-like Sb2S3 dendrites processed in conventional hydrothermal

Large-scale rod-like antimony sulfide (Sb₂S₃) dendrites have been prepared by hydrothermal method using antimony chloride (SbCl₃), citric acid and thioacetamide as raw materials at 160 °C for 12 h. The powder X-ray diffraction pattern shows the Sb₂S₃ crystals belong to the orthorhombic phase with calculated lattice parameters a = 1.120 nm, b = 1.128 nm and c = 0.3830 nm. The quantification of energy dispersive X-ray spectrometry analysis peaks gives an atomic ratio of 2:3 for Sb:S. Transmission electron microscopy micrograph studies reveal the appearance of the as-prepared Sb₂S₃ is dendrites-like which is composed of nanorods with the typical width of 300-500 nm and length of 5-20 µm. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of rod-like Sb₂S₃ dendrites is proposed.     

Properties of (Bi2Sb5Se3Te6I3)1 ? xMx (M = Ce, Pr) solid solutions

The effect of doping with Ce and Pr on the physicochemical properties of Bi₂Sb₅Se₃Te₆I₃ has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The results demonstrate that n-type Bi₂Sb₅Se₃Te₆I₃ dissolves 3.5 at % Ce. The Bi₂Sb₅Se₃Te₆I₃-Ce system has a eutectic at 10 mol % Ce, which melts at 360°C. The Pr solubility in Bi₂Sb₅Se₃Te₆I₃ is 4 at %. This system has a peritectic point at 10 at % Pr, with a peritectic temperature of 550°C.     

The system Ag2Se-Ho2Se3 in the 0-50 mol.% Ho2Se3 range and the crystal structure of two polymorphic forms of AgHoSe2

The phase diagram of the Ag₂Se-Ho₂Se₃ system in the range of 0-50 mol.% Ho₂Se₃ was constructed with the results of XRD and differential thermal analysis. A dimorphous compound exists in the system at the equimolar ratio of the components. The investigated part of the Ag₂Se-AgHoSe₂ diagram is of the eutectic type with the eutectic coordinates 7 mol.% Ho₂Se₃ and 1125 K. The crystal structure of the high-temperature modification of AgHoSe₂ was studied by X-ray powder diffraction method. α-AgHoSe₂ is described as a NaCl structure (space group ) with the lattice parameter а = 5.7623(3) Å. Atomic parameters were calculated in the isotropic approximation (R_I = 0.0434 and R_Р = 0.0636). The crystal structure of β-AgHoSe₂ was determined by X-ray structure analysis and was refined to R = 0.0487.