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Elemental Te and Cd are successfully recovered from CdTe via a combinatorial process involving chemical vapor transport (CVT) using sulfur as transport agent giving elemental Te being deposited. Separation is successfully enabled by the first process for CVT of Te starting with CdTe. Cd is subsequently recovered by an oxidation of the formed CdS to CdO followed by reduction to Cd metal with natural gas, in which Cd can also be separated via the gas phase. Hereby, the process addresses the main critical elements of the active material in thin film CdTe solar cells regarding both, scarcity and toxicity. Both, closed and open systems were investigated displaying more or less thermodynamic control of the system. Transport rates were determined for the closed system as well as for an open system working with sulfur vapour at moderate temperatures below and close to the boiling point of sulfur. Excellent purity of tellurium was achieved already by the initial transport, leading to low Cd2+ concentrations in the obtained Te being below the quantification limit of microwave plasma‐atomic emission spectroscopy (MP‐AES) (≪0.05 wt %). [ABSTRACT FROM AUTHOR]

Ternary chalcogenide PbGa2Se4 with high resistivity, photosensitivity, and excellent nonlinear properties, exhibits a potential application in optoelectronic and nonlinear optical devices. However, the preparation of large‐sized pure PbGa2Se4 crystals is challenging due to the presence of peritectic reaction L+α(Ga2Se3)→PbGa2Se4${\mathrm{L}} + {{\alpha}}({G{a}_2S{e}_3}) \to PbG{a}_2S{e}_4$ and a narrow homogeneity region. Here, a "quenching‐annealing" method (quenching at 850 °C in ice water, and then annealing at 650 °C for 250 h by reheating) is developed to eliminate the PbSe second phase during the synthesis. Subsequently, the PbGa2Se4 single crystals are successfully grown using chemical vapor transport (CVT) with the I2 as the transport agent. The resulting crystal exhibits the crystal structure belonging to Fddd space group with the lattice parameters of a = 12.7192 Å, b = 21.2831 Å, and c = 21.5226 Å. Additionally, it possesses a wide bandgap (≈2.26 eV), high resistivity (6.59 × 1012 Ω·cm), and defect density calculated via space charge limited current measurement (SCLC) as 2.46 × 1011 cm−3. Photodetectors based on these as‐grown crystals demonstrate exceptional photosensitivity along with a high detectivity (3.2 × 108 Jones). [ABSTRACT FROM AUTHOR]

Three‐dimensional (3D) charge‐written periodic peak and valley nanoarray surfaces are fabricated on a (112¯0$11\bar{2}0$) ZnO single crystal grown via chemical vapor transport. Because the grown ZnO crystals exhibit uniform n‐type conduction, 3D periodic nanoarray patterns are formed via oxygen annealing. These periodically decorated structures show that the peak arrays are conducting at the nanoampere level, whereas the valley arrays are less conductive. Energy dispersive spectroscopy indicates that the valley arrays are deficient in zinc by ≈4–6 at%, and that the peak arrays are deficient in oxygen, respectively. Kelvin probe force microscopy reveals the presence of periodic wiggles featuring variations of ≈70–140‐meV between the peak and valley arrays. A significant decrease in the Fermi level of the valley region is observed (≈190 meV), which corresponds to a high zinc vacancy doping density of 2 × 1018 cm−3. This result indicates the periodic generation of an extremely large electric field (≈11 000 V cm−1) in the vicinity of the peak–valley arrays. Computational analysis corroborates the experimentally observed generation of VZn and the preferential formation of surface protrusions on ZnO (112¯0$11\bar{2}0$) rather than on (0001), based on surface effects, along with the generation of peak and valley features. [ABSTRACT FROM AUTHOR]

This work investigates the transport properties of layered black phosphorus (BP) grown by the chemical vapor transport (CVT). The electrical measurements are carried out at a temperature ranging from 300 to 2 K and a magnetic field up to 16 Tesla. The CVT‐grown BP exhibits p‐type conduction with an acceptor's 14–1.2 meV activation energy. The concentration of ionized acceptors is 1.2×1017cm−3$1.2 \times {10^{17}}{\rm{c}}{{\rm{m}}^{ - 3}}$ Moreover, the Hall mobility is found to be 138 cm2V−1s−1 and 4 × 104 cm2V−1s−1, respectively, at room temperature and 2 K. This work reveals the potential of CVT synthesis as a simple, nontoxic, and cheap technique to make high‐quality BP crystals with high carrier mobility ready as a solid foundation for BP single‐crystal application. [ABSTRACT FROM AUTHOR]

Substitutional doping of 2D transition metal dichalcogenides (TMDCs) has been recognized as a promising strategy to tune their optoelectronic properties for a wide array of applications. However, controllable doping of TMDCs remains a challenging issue due to the natural doping of these materials. Here, the controllable growth of Ti‐doped MoS2 monolayers is demonstrated via the chemical vapor transport method, and the atomic embedded structure is confirmed by scanning transmission electron microscope with a probe corrector measurements. Furthermore, the grown Ti‐doped MoS2 monolayer exhibits giant photoluminescence (PL), 85‐fold stronger than a pristine MoS2 monolayer prepared by the same method. The giant PL enhancement is attributed to dopant‐induced O‐Ti‐S units and improved interaction between the monolayer and the mica substrate, increasing the photoluminescence quantum yield and facilitating radiation recombination. The successful growth of Ti‐doped MoS2 monolayer and the improvement of its optical and electrical properties by Ti doping may provide a promising method to engineer the optoelectronic properties of 2D TMDCs materials. [ABSTRACT FROM AUTHOR]

Fabrication of shape memory alloy (SMA) components based on NiTi is challenging due to the precision with which elemental composition and microstructure must be controlled during processing to achieve desired shape memory behavior. Herein, a method to control chemistry in an NiTi SMA via halide‐activated pack equilibration (SHAPE) against a constant chemical potential reservoir is described. To demonstrate the efficacy of the SHAPE process, an initially titanium‐deficient specimen (pure nickel foam) has been equilibrated against an excess of an intimately mixed two‐phase pack (NiTi + Ti2Ni) in the presence of a vapor phase transport agent (iodine). The two‐phase pack regulates chemical potentials in this two‐component system in accordance with Gibbs' phase rule. Ti‐rich NiTi foams thus produced exhibit reproducible and well‐defined phase transformation behaviors. The SHAPE process is advantageous for the fabrication of shape memory components of varying areal dimension, shape, and/or complexity owing to independence of the equilibrium state of the system from either the initial state of the specimen or the details of the process kinetics. Current limitations and prospects for the application of this method to improve the quality of SMA components are briefly discussed. [ABSTRACT FROM AUTHOR]

Cu2OSeO3 single crystals are grown with an optimized chemical vapor transport technique using SeCl4 as a transport agent (TA). The optimized growth method allows to selectively produce large high‐quality single crystals. The method is shown to consistently produce Cu2OSeO3 crystals of maximum size 8 × 7 × 4 mm with a transport duration of around three weeks. It is found that this method, with SeCl4 as TA, is more efficient and simple compared with the commonly used growth techniques reported in literature with HCl gas as TA. The Cu2OSeO3 crystals have very high quality and their absolute structures are fully determined by simple single‐crystal X‐ray diffraction. Enantiomeric crystals with either left‐ or right‐handed chiralities are observed. The magnetization and ferromagnetic resonance data show the same magnetic phase diagram as reported earlier. [ABSTRACT FROM AUTHOR]

In this work, the ZnO:Ga (GZO) single crystals are grown by the chemical vapor transport (CVT) method. The as‐grown crystals are annealed under an oxygen atmosphere at different temperatures. The GZO crystal's structure and its optical and electrical properties are characterized by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, X‐ray diffraction (XRD), UV‐VIS spectrophotometry, and variable‐temperature Hall‐effect measurement. The XPS results indicate that the valence states of the majority of gallium atoms in the GZO crystals undergo transition from the metallic (Ga0) to the non‐metallic state (Gax+) with increasing annealing temperature. The Raman and XRD results show that the compressive stress along the biaxial c‐axis on GZO crystals increases gradually with annealing temperature. Meanwhile, the GZO crystal's transmittance within the range of 300 to 1000 nm is improved significantly from being opaque to about 57%. The GZO crystals exhibit a decrease in free‐carrier concentration (1020–1019 cm−3), an increase in carrier mobility (77.8–87.9 cm2/V−1s−1) and resistivity (10−4–10−2 Ω·cm). The annealed GZO crystal's carrier concentration is practically independent of temperature (90–300 K). These results show that the free‐carrier concentrations are affected by the change of valence states in gallium atoms present in the GZO crystal. [ABSTRACT FROM AUTHOR]

Rhenium disulfide (ReS2) single crystals are grown by chemical vapor transport technique. Powder X‐ray diffraction analysis of the single crystals shows them to possess ReS2 phase with triclinic unit cell structure. Energy dispersive analysis of X‐rays shows the crystals to be slightly rich in sulfur and deficient in rhenium. The optical bandgap obtained of the as‐grown single crystals is 1.35 eV. The surface morphology study done by scanning electron microscopy shows that the crystal surface to be flat with layer edges, such observation states that the growth mechanism of crystal have happened by mechanism of sheet spreading. The transmission and diffraction mode electron microscopy shows the single crystals to be layered and crystalline, respectively. The Raman peaks are well assigned to the ReS2. Thermogravimetric and differential thermogravimetric analysis shows the single crystals to disintegrate by two steps. The differential thermal analysis shows that the ReS2 possesses initial endothermic followed by exothermic nature for fast heating rates. In case of a slow heating rate of 10 K min−1, other than endothermic followed by exothermic, the end temperature range shows endothermic nature. The kinetic parameters determined by Kissinger relation shows the single‐crystal samples to disintegrate at a higher temperature range. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) anisotropic rhenium diselenide (ReSe2) has attracted lots of attention due to its promising applications in electronics and optoelectronics. However, controlled synthesis of high quality ultrathin ReSe2 remains as a challenge. Here we developed an approach for synthesizing high quality 2D ReSe2 flakes with a thickness down to monolayer by chemical vapor transport (CVT) through carefully tuning the growth kinetics. The atomic structures and anisotropy of the obtained ReSe2 flakes were intensively characterized with scanning transmission electron microscope and angle‐resolved polarized Raman spectroscopy. Field‐effect transistors fabricated on the CVT‐grown ReSe2 flakes showed n‐type semiconducting behavior with an on/off current ratio of 105 and a mobility up to ∼5 cm2 V−1 s−1, which is comparable to mechanically exfoliated flakes and is obvious higher than the samples synthesized with other approaches. This study not only make high quality 2D ReSe2 easily accessible for both fundamental and application explorations but also sheds new lights on the chemical synthesis of other anisotropic 2D materials. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) PtSe2 shows the most prominent layer‐dependent electrical properties among various 2D materials and high catalytic activity for hydrogen evolution reaction (HER), and therefore, it is an ideal material for exploring the structure–activity correlations in 2D systems. Here, starting with the synthesis of single‐crystalline 2D PtSe2 with a controlled number of layers and probing the HER catalytic activity of individual flakes in micro electrochemical cells, we investigated the layer‐dependent HER catalytic activity of 2D PtSe2 from both theoretical and experimental perspectives. We clearly demonstrated how the number of layers affects the number of active sites, the electronic structures, and electrical properties of 2D PtSe2 flakes and thus alters their catalytic performance for HER. Our results also highlight the importance of efficient electron transfer in achieving optimum activity for ultrathin electrocatalysts. Our studies greatly enrich our understanding of the structure–activity correlations for 2D catalysts and provide new insight for the design and synthesis of ultrathin catalysts with high activity. [ABSTRACT FROM AUTHOR]

A variety of processes of crystal growth proceeds via the gas phase. If the initial solid material is volatilized in a heterogeneous reaction under presence of a gaseous reactant, the transport agent, the term Chemical Vapor Transport Reaction (CVT) is applied. Crystallization processes by CVT are known for both elements, intermetallics, binary and complex oxides, halides, chalcogenides, and pnictides. Even if the formation of volatile halides is a common feature of almost all vapor transport reactions, significant differences are there concerning the choice of a suitable transport agent depending on the nature of the initial solid phase. Actually, the appropriateness of transport agents for the respective transport reaction can be described in a thermodynamic way. Besides some basic principles for systematic evaluation more practical recommendations for suitable experimental conditions are given for CVT of different classes of inorganic materials. [ABSTRACT FROM AUTHOR]

Developing controlled approaches for synthesizing high-quality two-dimensional (2D) semiconductors is essential for their practical applications in novel electronics. The application of chemical vapor transport (CVT), an old single-crystal growth technique, has been extended from growing 3D crystals to synthesizing 2D atomic layers by tuning the growth kinetics. Both single crystalline individual flakes and continuous films of 1 L MoS2 were successfully obtained with CVT approach at low growth temperatures of 300-600 °C. The obtained 1 L MoS2 exhibits high crystallinity and comparable mobility to mechanically exfoliated samples, as confirmed by both atomic resolution microscopic imaging and electrical transport measurements. Besides MoS2, this method was also used in the growth of 2D WS2, MoSe2, Mo xW1− xS2 alloys, and ReS2, thus opening up a new way for the controlled synthesis of various 2D semiconductors. [ABSTRACT FROM AUTHOR]

The standard entropy of compounds In2 M3O12 ( M = Mo, W) were determined to be S°298 = 390 ± 6 ( M = Mo] and S°298 = 404 ± 6 J ·mol-1 ·K-1 ( M = W). The entropies of formation from the binary oxides are Δ S°R, 298 = 52 J ·mol-1 ·K-1 ( M = Mo] and Δ S°R, 298 = 72 J ·mol-1 ·K-1 ( M = W). Both compounds possess positive enthalpies of formation from the oxides at 298 K and are entropically stabilized. Transition enthalpies of the monoclinic to orthorhombic phase transition were measured for In2M3O12 by differential scanning calorimetry. Crystals of In2M3O12 (size up to a few mm) were deposited by means of chemical vapor transport along a temperature gradient Δ T = 100 K using transport agent chlorine. Deposition rates are between 0.2 and about 15 mg ·h-1, depending on mean transport temperature and amount of chlorine. Experimental results were compared to predictions by means of thermodynamic modelling. A detailed analysis of the chemical vapor transport behavior was carried out regarding gaseous compounds involved in the transport process, dominant transport reactions and influence of moisture content. [ABSTRACT FROM AUTHOR]

The solid solutions (V1- xW x)OPO4 with β-VOPO4 structure type (0.0 ≤ x ≤ 0.01) and αII-VOPO4 structure type (0.04 ≤ x ≤ 0.26) were obtained from mixtures of VVOPO4 and WVOPO4 by conventional solid state reactions and by solution combustion synthesis. Single crystals of up to 3 mm edge length were obtained by chemical vapor transport (CVT) (800 → 700 °C, Cl2 as a transporting agent). Single crystal structure refinements of crystals at x = 0.10 [ a = 6.0503(2) Å, c = 4.3618(4) Å, R1 = 0.021, wR2 = 0.058, 21 parameters, 344 independent reflections] and x = 0.26 [ a = 6.0979(2) Å, c = 4.2995(1) Å, R1 = 0.030, wR2 = 0.081, 21 parameters, 346 independent reflections] confirm the αII-VOPO4 structure type ( P4/ n, Z = 2) with mixed occupancy V/W for the metal site. Due to the specific redox behavior of W5+ and V5+, solid solutions (V1- xW x)OPO4 should be formulated as (VIV xVV1-2 xWVI x)OPO4. The valence states of vanadium and tungsten are confirmed by XPS measurements. V4+ with d1 configuration was identified by EPR spectroscopy and magnetic measurements. Electronic spectra of the solid solutions show the IVCT(V4+ → V5+) and the LMCT(O2- → V5+). (V0.74W0.26)OPO4 powders exhibit semi-conducting behavior ( Eg = 0.7 eV). [ABSTRACT FROM AUTHOR]

Single crystals of tetragonal β-Fe1.00Se were grown from polycrystalline material by chemical vapor transport reaction at temperatures below 723 K using AlCl3 as transport additive. The plate-shaped single crystals have edge lengths up to 4 mm. The single crystals display complete diamagnetic shielding 4π χ ≈ -1 below the superconducting transition. [ABSTRACT FROM AUTHOR]

Two solid solution series exist in the system MgMoO4-NiMoO4. The α-Ni1- yMg yMoO4 solution series, isostructural to α-NiMoO4, is thermodynamically stable at ambient conditions for compositions between 0 % and about 75 % magnesium content. The solution series β-Mg1- xNi xMoO4, isostructural to MgMoO4 and the high temperature β modification of NiMoO4, is thermodynamically stable at ambient conditions for compositions with < 25 % nickel content. A complete solid solution series β-Mg1- xNi xMoO4 exists at higher temperatures (> 823 K). The transition temperature for the α → β transition decreases with increasing magnesium content. The coexistence of both polymorphs at room temperature in samples with a wide range of composition is a result of the kinetic inhibition of the phase transition β → α. The chemical vapor transport of β-Mg1- xNi xMoO4 solid solutions with chlorine was investigated. Crystals with a nickel content up to 25 % were synthesized in temperature gradients 1273 K → 1223 K or 1273 K → 1173 K. Deposited nickel richer crystals are destroyed during cooling down to room temperature due to the phase transition. The observed distinctive nickel enrichment during the transport process is in good agreement with predictions by thermodynamic modeling. [ABSTRACT FROM AUTHOR]

The experimental observation of intrinsic ferromagnetism in single layered chromium trihalides CrX3 (X = Cl, Br, I) has gained outstanding attention recently due to their possible implementation in spintronic devices. However, the reproducible preparation of highly crystalline chromium(III) halide nanolayers without stacking faults is still an experimental challenge. As chromium trihalides consist of adjacent layers with weak interlayer coupling, the preparation of ultrathin CrX3 nanosheets directly on substrates via vapor transport proves as an advantageous synthesis technique. It is demonstrated that vapor growth of ultrathin highly crystalline CrX3 micro‐ and nanosheets succeeds directly on yttrium stabilized zirconia substrates in a one‐step process via chemical vapor transport (CVT) in temperature gradients of 100 K (600 °C → 500 °C for CrCl3 and 650 °C → 550 °C for CrBr3 or CrI3) without a need for subsequent delamination. Due to simulation results, optimization of synthesis conditions is realized and phase pure CrX3 nanosheets with thicknesses ≤25 nm are obtained via short term CVT. The nanosheets morphology, crystallinity, and phase purity are analyzed by several techniques, including microscopy, diffraction, and spectroscopy. Furthermore, a potential subsequent delamination technique is demonstrated to give fast access to CrX3 monolayers using the example of CrCl3. [ABSTRACT FROM AUTHOR]

Recently, 2D electron gases have been observed in atomically thin semiconducting crystals, enabling the observation of rich physical phenomena at the quantum level within the ultimate thickness limit. However, the observation of 2D electron gases and subsequent quantum Hall effect require exceptionally high crystalline quality, rendering mechanical exfoliation as the only method to produce high‐quality 2D semiconductors of black phosphorus and indium selenide (InSe), which hinder large‐scale device applications. Here, the controlled one‐step synthesis of high‐quality 2D InSe thin films via chemical vapor transport method is reported. The carrier Hall mobility of hexagonal boron nitride (hBN) encapsulated InSe flakes can be up to 5000 cm2 V−1 s−1 at 1.5 K, enabling to observe the quantum Hall effect in a synthesized van der Waals semiconductor. The existence of the quantum Hall effect in directly synthesized 2D semiconductors indicates a high quality of the chemically synthesized 2D semiconductors, which hold promise in quantum devices and applications with high mobility. [ABSTRACT FROM AUTHOR]