Unusual Solid Solutions in the System Ge‐Sb‐Te: The Crystal Structure of 33R‐Ge4−xSb2−yTe7 (x,y ≈ 0.1) is Isostructural to that of Ge3Sb2Te6

Whereas for a series of layered compounds with the general formula (GeTe)_n(Sb₂Te₃)_m the stoichiometry allows to predict the structure type and the average thickness of the hexagonal atom layers, these rules are not generally applicable for GeTe‐rich compounds like Ge₄Sb₂Te₇. A 39R layer stacking is expected, however, single crystal diffraction studies reveal a 33R layered structure ( , a = 4.1891(5) Å, c = 62.169(15), R = 0.047) closely related to that of Ge₃Sb₂Te₆. This is also corroborated by the average layer thickness that can be determined from the strong reflections of powder patterns and exhibits a direct relation to the structure type. Mixed occupancy of cation positions with Ge and Sb and possibly defects allow this unusual range of homogeneity. Bulk material of the kinetically stable compound can be synthesized by quenching stoichiometric melts of the pure elements and subsequent annealing.     

Phase equilibria in the InS-Sb2Te3 system

The interaction character of the InS-Sb₂Te₃ system was studied by differential thermal analysis, X-ray powder diffraction, microstructure examinations, microhardness measurements, and density determinations, and its phase diagram was constructed. The InS-Sb₂Te₃ phase diagram is a partially non-quasi-binary section of the In,Sb∥S,Te ternary reciprocal system. Two compounds are formed in the InS-Sb₂Te₃ system, namely: In₃Sb₂S₃Te₃ and InSb₂Te₃S. Sb₂Te₃-based solid solutions at room temperature have an extent of up to 6 mol % InS, while InS-based solid solutions are virtually nonexistent.     

Towards Antimonene and 2D Antimony Telluride through Electrochemical Exfoliation

Two-dimensional (2D) layered antimony (Sb) and antimony telluride (Sb₂Te₃) are two valuable materials for optoelectronic devices and thermoelectric applications. Preparing high-quality sheets of these materials is the initial phase to promote their expected issues. Herein, micrometer-sized few-to-multilayered sheets of Sb and Sb₂Te₃ have been obtained by electrochemical exfoliation. The layered rhombohedral Sb was exfoliated in Na₂SO₄ and Li₂SO₄ electrolytes by anodic–cationic intercalation, and Sb₂Te₃ was exfoliated in Na₂SO₄. These findings are important contributions for the solution-based room-temperature electrochemical exfoliation, which is stable under glove-box-free conditions, to further improve the production of high-quality exfoliated sheets.     

Molecular Precursors for the Phase‐Change Material Germanium‐Antimony‐Telluride,Ge2Sb2Te5 (GST)

This review provides an overview of the precursor chemistry that has been developed around the phase‐change material germanium‐antimony‐telluride, Ge₂Sb₂Te₅ (GST). Thin films of GST can be deposited by employing either chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques. In both cases, the success of the layer deposition crucially depends on the proper choice of suitable molecular precursors. Previously reported processes mainly relied on simple alkoxides, alkyls, amides and halides of germanium, antimony, and tellurium. More sophisticated precursor design provided a number of promising new aziridinides and guanidinates.     

Preparation of Bi0.4Sb1.6Se3xTe3(1−x) hexagonal rods and effect of Se on structure and electrical property

In the current study, novel hexagonal rods based on Bi_0.4Sb_1.6Te₃ raw materials and dispersed with x amounts of Se (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in the form Bi_0.4Sb_1.6Se_3xTe_3(1−x) were synthesized via a standard solid-state microwave route. The morphologies of these rods were explored using field emission scanning electron microscopy (FESEM). The crystalline of the powders were examined by X-ray diffraction (XRD), which showed that the powders of 0.0 ≤ x ≤ 0.8 samples can be indexed as the rhombohedral phase, whereas the sample with x = 1.0 has an orthorhombic phase structure. The influence of variations in Se content on thermoelectric properties was studied in the temperature range of 300–523 K. The alloying of Se in Bi_0.4Sb_1.6Te₃ effectively caused a decrease in hole concentration and, thus, a decrease in electrical conductivity and an increase in Seebeck coefficient. The maximal power factor measured in the present work was 7.47 mW/m K² at 373 K for the x = 0.8 sample.     

A New Strategy for Realizing the Conversion of “Homo–Hetero–Homo” Heteroepitaxial Growth in Bi2Te3 and the Thermoelectric Performance

Uncovering the reason for structure‐dependent thermoelectric performance still remains a big challenge. A low‐temperature and easily scalable strategy for synthesizing Bi₂Te₃ nanostring hierarchical structures through solution‐phase reactions, during which there is the conversion of “homo–hetero–homo” in Bi₂Te₃ heteroepitaxial growth, is reported. Bi₂Te₃ nanostrings are obtained through the transformation from pure Bi₂Te₃ hexagonal nanosheets followed by Te?Bi₂Te₃ “nanotop” heterostructures to Bi₂Te₃ nanostrings. The growth of Bi₂Te₃ nanostrings appears to be a self‐assembly process through a wavy competition process generated from Te and Bi³⁺. The conversion of homo–hetero–homo opens up new platforms to investigate the wet chemistry of Bi₂Te₃ nanomaterials. Furthermore, to study the effect of morphologies and hetero/homo structures, especially with the same origin and uniform conditions on their thermoelectric properties, the thermoelectric properties of Bi₂Te₃ nanostrings and Te?Bi₂Te₃ heterostructured pellets fabricated by spark plasma sintering have been investigated separately.     

Estimation of kinetic parameters for the phase change memory materials by DSC measurements

The non-isothermal method for estimating the kinetic parameters of crystallization for the phase change memory (PCM) materials was discussed. This method was applied to the perspective PCM material of Ge₂Sb₂Te₅ with different Bi contents (0, 0.5, 1, 3 mass%) for defining the kinetic triplet. Rutherford backscattering spectroscopy and X-ray diffraction were used to carry out elemental and phase analysis of the deposited films. Differential scanning calorimetry at eight different heating rates was used to investigate kinetics of thermally induced transformations in materials. Dependences of activation energies of crystallization (E _a) on the degree of conversion were estimated by model-free Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, Tang and Starink methods. The obtained values of E _a were quite close for all of these methods. The reaction models of the phase transitions were derived with using of the model-fitting Coats–Redfern method. In order to find pre-exponential factor A at progressive conversion values, we used values of E _a already estimated by the model-free isoconversional method. It was established that the crystallization processes in thin films investigated are most likely describes by the second and third-order reactions models. Obtained kinetic triplet allowed predicting transition and storage times of the PCM cells. It was found that thin films of Ge₂Sb₂Te₅ + 0.5 mass% Bi composition can provide the switching time of the phase change memory cell less than 1 ns. At the same time, at room temperature this material has a maximum storage time among the studied compositions.     

Propriétés thermiques et optiques des verres du système Sb2S3–As2S3–Sb2Te3

Thermal and optical properties of glasses of the Sb₂S₃–As₂S₃–Sb₂Te₃ system. The glass-forming region of Sb₂S₃–As₂S₃–Sb₂Te₃ is very wide. The As₂S₃ compound supports the formation of prepared glasses and their stability. They have only one glass-transition temperature (T_g), which varies from 167 to 214 °C. It drops when the content of Sb₂Te₃ increases. This semi-metal compound supports the crystallization of glasses in several stages. Whereas the optical gap (E_g) increases with the content of As₂S₃ in the Sb₂S₃–As₂S₃ and Sb₂Te₃–As₂S₃ binary systems, it is practically constant in the ternary one on the cut with 20% of Sb₂Te₃, and is worth on average 1.04 eV.     

Phase equilibrium in the Sb2Se3-Gd2Te3 system

The Sb₂Se₃-Gd₂Te₃ system was studied using differential thermal analysis, X-ray powder diffraction, and microstructure examination. This is a quasi-binary system. Sb₂Se₃-based solubility at 300 K is 10 mol % Gd₂Te₃. The eutectic contains 20 mol % Gd₂Te₃ and melts at 760 K. One incongruently melting compound (870 K) of composition GdSbTe_1.5Se_1.5 was found in the system.     

Processing and characterization of new oxy-sulfo-telluride glasses in the Ge-Sb-Te-S-O system

New oxy-sulfo-telluride glasses have been prepared in the Ge-Sb-Te-S-O system employing a two-step melting process which involves the processing of a chalcogenide glass (ChG) and subsequent melting with TeO₂ or Sb₂O₃. The progressive incorporation of O at the expense of S was found to increase the density and the glass transition temperature and to decrease the molar volume of the investigated oxy-sulfo-telluride glasses. We also observed a shift of the vis-NIR cut-off wavelength to longer wavelength probably due to changes in Sb coordination within the glass matrix and overall matrix polarizability. Using Raman spectroscopy, correlations have been shown between the formation of Ge- and Sb-based oxysulfide structural units and the S/O ratio. Lastly, two glasses with similar composition (Ge₂₀Sb₆S₆₄Te₃O₇) processed by melting the Ge₂₃Sb₇S₇₀ glass with TeO₂ or the Ge₂₃Sb₂S₇₂Te₄ glass with Sb₂O₃ were found to have slightly different physical, thermal, optical and structural properties. These changes are thought to result mainly from the higher moisture content and sensitivity of the TeO₂ starting materials as compared to that of the Sb₂O₃.     

Molecular building blocks for solid‐state chalcogenides: solvothermal synthesis of [Mn(en)3]Te4 and [Fe(en)3]2(Sb2Se5)

Two new molecular metal chalcogenides, tris­(ethyl­enedi­amine‐N,N′)­manganese(II) tetratelluride, [Mn(C₂H₈N₂)₃]Te₄, (I), and bis­[tris­(ethyl­enedi­amine‐N,N′)­iron(II)] penta­seleno­diantimonate(III), [Fe(C₂H₈N₂)₃]₂(Sb₂Se₅), (II), containing the isolated molecular building blocks Te₄^2? and Sb₂Se₅^4?, have been synthesized by solvothermal reactions in an ethyl­enedi­amine solution at 433 K. The anion Te₄^2? in (I) is a zigzag oligometric chain with Te—Te bond lengths in the range 2.709–2.751 Å. There is a very short contact [3.329 (1) Å] between a pair of neighboring Te₄^2? anions. In (II), each Sb atom is surrounded by three Se atoms to give a tripodal coordination. One of the three independent Se atoms is a μ₂‐bridging ligand between two Sb atoms; the other two are terminal.     

Color Tuning in Garnet Oxides: The Role of Tetrahedral Coordination Geometry for 3 d Metal Ions and Ligand–Metal Charge Transfer (Band‐Gap Manipulation)

We explored garnet‐structured oxide materials containing 3d transition‐metal ions (e.g., Co²⁺, Ni²⁺, Cu²⁺, and Fe³⁺) for the development of new inorganic colored materials. For this purpose, we synthesized new garnets, Ca₃Sb₂Ga₂ZnO₁₂ ( I ) and Ca₃Sb₂Fe₂ZnO₁₂ ( II ), that were isostructural with Ca₃Te₂Zn₃O₁₂. Substitution of Co²⁺, Ni²⁺, and Cu²⁺ at the tetrahedral Zn²⁺ sites in I and II gave rise to brilliantly colored materials (different shades of blue, green, turquoise, and red). The materials were characterized by optical absorption spectroscopy and CIE chromaticity diagrams. The Fe³⁺‐containing oxides showed band‐gap narrowing (owing to strong sp–d exchange interactions between Zn²⁺ and the transition‐metal ion), and this tuned the color of these materials uniquely. We also characterized the color and optical absorption properties of Ca₃Te₂Zn_3−x Co_x O₁₂ (0<x ≤2.0) and Cd₃Te₂Zn_3−x Co_x O₁₂ (0<x ≤1.0), which display brilliant blue and green‐blue colors, respectively. The present work brings out the role of the distorted tetrahedral coordination geometry of transition‐metal ions and ligand–metal charge transfer (which is manifested as narrowing of the band gap) in producing brilliantly colored garnet‐based materials.     

The heat capacity of solid antimony telluride Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The literature data on the heat capacity of solid antimony telluride over the range 53–895 K were analyzed. The heat capacity of Sb₂Te₃ was measured over the range 350–700 K on a DSM-2M calorimeter. The equation for the temperature dependence was suggested. The thermodynamic functions of Sb₂Te₃ were calculated over the range 298.15–700 K.     

Investigation of HfO2 doping on GeTe for phase change memory

The phase change characteristics of HfO₂ doping on GeTe thin films were investigated by X-ray photoelectron spectroscopy, X-ray diffraction patterns, scanning electron microscope, atom force microscopy, and in situ resistance-temperature measurements. It is shown that the crystallization of amorphous GeTe film could be suppressed by the incorporation of HfO₂, which had a favorable effect on the archival life stability. The activation energy for crystallization increased from 2.36 to 4.69 eV, and the temperature for 10 years data retention increased from 108 to 187 °C with the increasing concentration of HfO₂ form 0 to 12 mol%. Meanwhile, the grain size and surface roughness decreased. Phase change memory based on GeTe–HfO₂ film was fabricated and characterized. A reversible phase change could be trigged by the pulse with at least 100 ns width which was shorter than that of Ge₂Sb₂Te₅ (500 ns). The resistance ratio between amorphous and crystalline states achieved 500 times. The minimum energy necessary for RESET operation of GeTe–HfO₂ based test cell was much smaller than that of Ge₂Sb₂Te₅-based one.     

Nonlinear Optical Switching Driven by the Lone Pair Electron Effect in a Hybrid Compound: (1S, 4S)-(+)-2-Aza-5-oxabicyclo[2.2.1] heptane)2[SbCl5]

In order to take advantage of hybrid materials in their structural diversity and richness of their photoelectric properties, the research in polar materials has been extended to metal-organic compounds in recent years. The main synthesis strategy is to use the molecular dynamics. Here, we describe that the second harmonic generation (SHG) switching effect can be effectively achieved by combination of coordination distortion of metal ions with s² electrons and molecular dynamics. We synthesized a noncentrosymmetric complex, (1S,4S)-(+)-2-aza-5-oxabicyclo[2.2.1]heptane)₂[SbCl₅], and found that it undergoes an isomorphic phase transition at 382 K. Accompanying the phase transition, the SHG experiences a switching process, and its strength changes from 0.2 times of that of KDP to only noise level. Systematic characterization reveals that the significant change of coordination distortion of the Sb³⁺ and the change of thermal motion of organic cations lead to the SHG switching effect. This finding shows that the combination of lone pair electron effect of metal ion and molecular dynamics characteristics would be a feasible strategy in development of polar hybrid materials.     

Projection of the liquidus surface of the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Gd<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> system

Phase equilibria in the Sb₂Te₃-Gd₂Te₃-Bi₂Te₃ ternary system have been studied using differential thermal analysis, namely, X-ray powder diffraction, microstructure examination, thermodynamic analysis, and microhardness and alloy density measurements. Phase diagrams of some polythermal joins and liquidus surface have been constructed. The regions of primary crystallization of phases and the coordinates of all invariant and univariant equilibria in the system under investigation have been established.     

The Sections GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–GeTe and GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–SnTe of the Quasi-Ternary System GeTe–Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–SnTe

By differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements, phase equilibria in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe were studied and their state diagrams were constructed. It was determined that these sections are quasi-binary sections of the eutectic type of the GeTe–Sb₂Te₃–SnTe system. The coordinates of the eutectic points in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe are (40 mol % GeTe, 700 K) and (30 mol % SnTe, 750 K), respectively. Regions of solid solutions based on the initial components in the sections were identified. Alloys in the regions of solid solutions are p-type semiconductors.     

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.     

Rb3Ti3Te11

Trirubidium trititanium undecatelluride, Rb₃Ti₃Te₁₁, has been synthesized from the reaction of titanium, tellurium, and Rb₂Te₃ at 773 K. Its structure has been determined from single‐crystal X‐ray data. It is composed of one‐dimensional [Ti₃Te₁₁^3?] chains built by face‐sharing pentagonal TiTe₇ bipyramids and distorted TiTe₆ octahedra. These chains adopt hexagonal closest packing along the [101] direction. Rb atoms are located among these chains. The wide range of Te—Te interactions makes the assignment of formal oxidation states impossible. The compound is isostructural with Cs₃Ti₃Te₁₁.