Single Crystal Form Research Articles

Enhanced thermoelectric performance of polycrystalline SnSe by doping with the heavy rare earth element Yb

As an environmentally friendly thermoelectric material, SnSe has attracted great attention because of its excellent performance in its single-crystal form. On the other hand, the better mechanical property and lower manufacturing cost of its polycrystalline counterpart with the better mechanical property and lower manufacturing cost can serve as a better candidate for widespread applications. Previous reports on p-type polycrystalline SnSe mainly focus on optimizing the carrier concentration by doping alkali metals or decreasing the lattice thermal conductivity by nanostructuring. Here, we report the effect of Yb doping on the thermoelectric properties of polycrystalline SnSe prepared by solvothermal synthesis. Through introducing Yb, the p-type carrier concentration is increased and the density of states at valence band maximum is distorted, which is revealed by DFT calculation, leading to an increase of the effective mass. Thus, the power factor has been markedly enhanced to 0.78 mW m−1 K−2 at 823 K (about 1.6 times that of undoped SnSe). Moreover, Yb doping in SnSe decreases the lattice thermal conductivity by intensifying the phonon scattering. As a result, a high zT of 1.1 at 823 K in Sn0.98Yb0.02Se is achieved along the in-plane direction. This work provides a new way for improving the thermoelectric properties of SnSe by modifying its valence band structure.

SYNTHESIS AND CHARACTERIZATION OF STRUCTURAL AND OPTICAL PROPERTIES OF NI-DOPED ZINC SULFIDE NANOPARTICLES

The band-gaps of wide band gap metal sulfide semiconductors such as ZnS, are significantly reduced when doped with transition metal ions Ni2+.The new composite materials offer promising and versatile applications in spintronic devices, solar cells and other optoelectronic devices, and in photonics etc. It has led to substantial modifications in methods of synthesis for ZnS nanoparticles. In this research work, we have synthesized ZnS nanoparticles via simple chemical precipitation method. ZnS nanoparticles have been characterized using UV-visible spectra and Raman spectroscopy. For morphological studies we have used scanning electron microscopy (SEM). The optical band gap has been evaluated from UV-vis-nir absorption spectrum of the particles. Raman spectroscopy is used to study the rotational, vibrational and other modes of the sample, as we are interested to reveal properties of nanoclusters treating as those as nano-molecules. We correlate the variations in properties with their structures. Our investigations confirm formation of large single crystals (nanomolecules) yielding resonant Raman peaks. It is further confirmed from SEM images of the samples. Nanoparticles have special properties other than bulk. Their surface energy contributions are entirely different from their bulk counterparts and play dominant role in its stability. Thus, we assign a special phase for them as “Nanophase”. The phenomenon of nano-cluster (aggregates) formation of nickel atoms via nucleation is also confirmed for high doping concentrations of nickel, which results into inverse trend for band-gap.

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

Synthesis and crystallization mechanism of EUO zeolite

Nucleation and growth of zeolites are closely related to the state of amorphous aluminosilicate precursors which may lead to different crystallization pathways. This article provided a deep understanding of the formation mechanisms of EUO from different precursors generated through hydrolysis of tetraethoxysilane (TEOS) at different temperatures as well as by introducing the aluminum source at different time. A combination of diffraction, NMR and microscopy techniques was applied to characterize the assembly and evolution of amorphous species during the synthesis of EUO zeolites. Hydrolysis temperature of TEOS was closely associated with the nucleation rate of EUO. The evolution of worm-like precursors to bulk precursors was accelerated when the gel was hydrolyzed at low temperature. Moreover, the introduction of sodium aluminate could also promote the nucleation when a homogeneous gel with uniform Si–Al distribution was formed. When the gel environment was non-uniform, amorphous-to-crystalline transformation involved a two-step pathway, beginning with the appearance of *MRE due to the existence of Si-rich regions, followed by inter-crystalline transformation to EUO. Such crystallization pathway led to the formation of EUO single crystal around 1.5 μm. Given that numerous zeolite syntheses involve the formation of metastable precursors with heterogeneous composition, the choice of gel preparation procedure in this study may be generalized to other related materials.

Ag/Co/B tri-doped TiO2/SiO2 film for enhancing photocatalytic degradation

Ag/Co/B tri-doped TiO2/SiO2 film was prepared by the sol–gel method, and the structure and properties of this film were characterized by the X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) test method, field emission scanning electron microscopy (FE-SEM), differential thermal analysis-thermogravimetry (DTA-TG), photoluminescence (PL), and UV-visible diffuse reflectance spectrum (UV-vis DRS). XRD results indicated that the film structure of this film conforms to the anatase single crystal form. The presence of SiO2 can inhibit the formation of brookite and prevent the conversion of anatase into rutile. BET and FE-SEM results revealed that the film had a higher specific surface area and smaller grain size compared with pure TiO2 film. DTA-TG results exposed that the film had excellent thermal stability at 450[Formula: see text]C. Due to the spectacular adsorption capacity of SiO2 and the Schottky barrier formed between Ag and TiO2, this film improved the h[Formula: see text]/e[Formula: see text] separation efficiency and optical absorption performance showed by PL results. UV-vis DRS results displayed that the band gap energy (2.47 eV) of the film was clearly lower than that of pure TiO2 film, due to the intermediate energy levels generated by Co and B ions doping. The photocatalytic activity of the film was verified by ultraviolet and visible light degradation experiments of two different organic pollutants. The experimental results exhibited that the film had excellent photocatalytic degradation ability and stability. Ultimately, a possible synergistic mechanism of photocatalysis was proposed in this paper.

A combined experimental and theoretical studies of two new decavanadatet: (C6N2H9)4[H2V10O28]·4H2O and (C7H9NF)4[H2V10O28]·2H2O

Two novel organic-inorganic decavanadate materials with protonated amines were prepared from acidified aqueous solution and characterized by single crystal X-Ray diffraction, thermogravimetric analysis and IR spectroscopy. (C6N2H9)4[H2V10O28]·4H2O (I) and (C7H9NF)4[H2V10O28]·2H2O (II), were isolated in single-crystal form. For both compounds, the crystal packing is governed by the formation of various non-covalent intermolecular forces between decavanadate anions, organic cations and water molecules. For both compounds, Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to in the crystal packing for both compounds are from O⋅⋅⋅H/H⋅⋅⋅O and H⋅⋅⋅H bonds. Furthermore, topological study of weak non-covalent interactions properties was theoretically carried out using DFT. The determined HOMO and LUMO levels were to estimate the charge transfer within the structure. The photoluminescence properties and UV–Vis absorption spectra have also been investigated. Both (I) and (II) possess photoluminescence properties and produce blue and green emissions, respectively, upon irradiation with violet light.

Fast Lead-Free Humidity Sensor Based on Hybrid Halide Perovskite

An environmentally friendly analog of the prominent methylammonium lead halide perovskite, methylammonium bismuth bromide (MA3Bi2Br9), was prepared and investigated in the form of powder, single crystals and nanowires. Complete characterization via synchrotron X-ray diffraction data showed that the bulk crystal does not incorporate water into the structure. At the same time, water is absorbed on the surface of the crystal, and this modification leads to the changes in the resistivity of the material, thus making MA3Bi2Br9 an excellent candidate for use as a humidity sensor. The novel sensor was prepared from powder-pressed pellets with attached carbon electrodes and was characterized by being able to detect relative humidity over the full range (0.7–96% RH) at ambient temperature. Compared to commercial and literature values, the response and recovery times are very fast (down to 1.5 s/1.5 s).

Investigation of Rare Earth-Containing Double Phosphates of the Type A3Ln(PO4)2 (Ln = Y, La, Pr, Nd, and Sm–Lu) as Potential Nuclear Waste Forms

A new series of rubidium rare earth double phosphates is presented. High-quality single crystals of Rb3Ln(PO4)2 (Ln = Y, La, Pr, Nd, and Sm–Lu) were grown via high-temperature flux growth methods. The Rb3Ln(PO4)2 (Ln = La, Pr, Nd, and Sm–Tb) phases crystallize in space group P21/m, and the Rb3Ln(PO4)2 (Ln = Y and Dy–Lu) phases crystallize in space group P31m. A thermally induced and reversible structural transition, due to a change in the denticity of a rare earth-ligated phosphate group, is observed between the two structures at a temperature that depends on the incorporated rare earth. High-entropy versions, Rb3[Eu0.2Gd0.2Tb0.2Dy0.2Ho0.2](PO4)2 and Rb3[Gd0.2Tb0.2Dy0.2Ho0.2Er0.2](PO4)2, of the double phosphate were prepared to assess how readily they could be obtained in single-crystal form. A high observed radiation damage tolerance and favorable density functional theory-calculated formation enthalpies for the trivalent actinide analogues of Rb3M(PO4)2 suggest likely successful actinide analogue syntheses in the future.

Temperature dependent bandgap in NaBi(WO4)2 single crystals

The double tungstates have been an attractive research interest due to their optoelectronic applications. In the present work, NaBi(WO4)2, one of the members of double tungstates family, was grown by Czochralski method as single crystal form and optically investigated. X-ray diffraction pattern presented three peaks associated with tetragonal scheelite crystalline structure. Optical properties of the crystal were studied by performing temperature-dependent transmission measurements between 10 and 300 K. The shift of the absorption edge to higher energies was observed with decrease of temperature. The analyses indicated that direct band gap energy increases from 3.50 to 3.60 eV when the temperature was decreased from room temperature to 10 K. The temperature dependency of bandgap was studied considering the Varshni model and fitting of the experimental data under the light of model presented the optical parameters of band gap energy at 0 K, rate of band gap change with temperature and Debye temperature as Eg(0) = 3.61 eV, γ = − 8.83 × 10−4 eV/K and β = 456 K, respectively. Urbach energies were also determined from the analyses as 122 and 113 meV for 10 and 300 K experimental data, respectively.

Synthesis, Crystal Structure and Properties of a new Hydrate of Manganese Thiocyanate with the Composition Mn(NCS)2(H2O)2

AbstractThe reaction of Mn(NCS)2 with 3‐cyanopyridine in water accidentally leads to the formation of single crystals of Mn(NCS)2(H2O)2 (1). If the synthesis is performed without 3‐cyanopyridine, the known tetrahydrate Mn(NCS)2(H2O)4 is formed. In the crystal structure of the new hydrate, the Mn2+ cations are linked by pairs of μ‐1,3‐bridging anionic ligands to chains, which are further connected via Mn(NCS)2(H2O)4 units into layers, that are additionally stabilized by intralayer hydrogen bonding. These layers are linked by interlayer hydrogen bonding into a 3D network. The structure of 1 shows strong similarities to that of both the tetrahydrate and of Mn(NCS)2. The synthesis from water always leads to the tetrahydrate, which is also obtained, when Mn(NCS)2 is stored in a humid atmosphere. Thermoanalytical measurements on the tetrahydrate show a more complicated behavior, which includes melting at about 46 °C and on cooling sometimes the dihydrate is observed. If the tetrahydrate is stored in vacuum at room temperature, the dihydrate forms before the transformation to the anhydrate is observed. Isothermic water sorption measurements prove, that at low humidity the dihydrate is obtained, which transforms into the tetrahydrate at higher humidities.

Magnetic properties of a highly ordered single crystal of the layered perovskite YBaCuFe0.95Mn0.05O5

The layered perovskite YBaCuFeO5 (YBCFO) is able to adopt chiral magnetic order up to unexpectedly high temperatures, paving the way to strong magnetoelectric coupling at room temperature. In this perovskite A-site cations are fully ordered whereas the occupancy of the B-sites strongly depend on the preparation process. Though the structure is not geometrically frustrated, the presence of partial Fe3+/Cu2+ disorder at the B-sites produces magnetic frustration. In an effort to increase the spin–orbit coupling in the system, we have synthesized and studied YBaCuFe0.95Mn0.05O5 in single crystal form, where the highly symmetric Fe3+ ions (3d5) are partially substituted with Jahn-Teller active 3d4 Mn3+ ions. We report the structural and magnetic properties of a highly ordered single crystal of this layered perovskite, which are presented in comparison with a polycrystalline specimen (three times more disordered). Single crystal neutron diffraction measurements reveal two collinear magnetic phases and the lack of incommensurate spiral order. The magnetic phases and transitions found in the crystal grown by the traveling solvent floating zone (TSFZ) method are fully described and analyzed in the light of its high level of Fe/Cu cationic order (∼90%).

Synthesis, Physicochemical, Thermal and Antioxidative Properties of Zn(II) Coordination Compounds with Pyrazole-Type Ligand

The reactions of pyrazole derivative, i.e., ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (L) with zinc halogenides in methanolic solution and zinc nitrate and zinc acetate in acetonic solution are described. The formulae of synthesized compounds are ZnL2Cl2 (1), [ZnL2Br2] (2), ZnL2I2·0.5MeOH (3), [Zn(L)2(H2O)4](NO3)2 (4), and {ZnL(OAc)2}2 (5). Two complexes are obtained in form of single crystals: [ZnL2Br2] (2) and [Zn(L)2(H2O)4](NO3)2 (4). Their crystal and molecular structure were determined by single-crystal X-ray structure analysis. The FTIR spectra of compounds prove the complex formation with all five zinc salts. The complexes are characterized by conductometric and thermoanalytical measurements, and their antioxidative activity was also tested by the scavenging effect on the DPPH radical. Conductometric results, solvolytic stability, and antioxidative activity of the compounds are in correlation.

Spontaneous moisture-driven formation of Cs2Pb1-xMxCl2I2 single crystals with M = Bi, In, Ga and Cr

Micrometer to millimeter platelets-like single crystals of the 2D-derivated perovskite structure Cs2PbCl2I2 were synthesized by a very simple route using the humid ambient environment surrounding a DMSO solution containing the salt precursors. Cs2Pb1-xMxCl2I2 formation was also evidenced by single crystal X-ray diffraction, with M = Bi, Ga, In and Cr. X-ray photoelectron spectroscopy (XPS) confirmed the presence of each dopant, with an amount of x ∼ 5 ato.% for the last three materials. For the Bi-doped sample, XPS showed a larger quantity of dopant that can be due to XPS difficulty to discriminate too close elements for a few nanometers of analysis or higher concentrations in some crystals due to the affinity of both elements to integrate this structure on the same crystallographic site. A decrease of Bi concentration was determined by ion-beam and XPS simultaneous analysis. Finally, a photoluminescence (PL) peak was observed at ∼420 nm for all samples. Peak widening and blue-shift can be ascribed to the doping, and attributed to photon recycling and radiative self-trapped states. These results show the great versatility of ionic substitution and adaptive optoelectronic properties of the 2D phase that is stable in temperature.

Large π-Conjugated Metal-Organic Frameworks for Infrared-Light-Driven CO2 Reduction.

It remains challenging to excite traditional photocatalysts through near-infrared (NIR) light. Attempts to use NIR-light-response materials for photochemical reduction usually suffer from inapposite band position due to extremely narrow band gaps. Here, we report that large π-conjugated organic semiconductor engineered metal-organic framework (MOF) can result in NIR-light-driven CO2 reduction catalyst with high photocatalytic activity. A series of mesoporous MOFs, with progressively increased macrocyclic π-conjugated units, were synthesized for tuning the light adsorption range and catalytic performance. Attainment of these MOFs in single-crystal form revealed the identical topology and precise spatial arrangements of constituent organic semiconductor units and metal clusters. Furthermore, the ultrafast spectroscopic studies confirmed the formation of charge separation state and the mechanism underlying photoexcited dynamics. This combined with X-ray photoelectron spectroscopy and in situ electron paramagnetic resonance studies verified the photoinduced electron transfer pathway within MOFs for NIR-light-driven CO2 reduction. Specifically, tetrakis(4-carboxybiphenyl)naphthoporphyrin) MOF (TNP-MOF) photocatalyst displayed an unprecedentedly high CO2 reduction rate of over 6630 μmol h-1 g-1 under NIR light irradiation, and apparent quantum efficiencies (AQE) at 760 and 808 nm were over 2.03% and 1.11%, respectively. The photocatalytic performance outperformed all the other MOF-based photocatalysts, even visible-light-driven MOF-based catalysts.

Thermal conductivity and management in laser gain materials: A nano/microstructural perspective

Heat generation and thermally induced failure has been a major challenge for high-power applications in solid state lasers. Improvements in the solid state laser ceramic fabrication process offer improved mechanical toughness and comparable thermal conductivity compared to single crystal counterparts. Equally enticing is the possibility of using materials with intrinsically superior thermal/mechanical properties that are not viable in the single crystal form. Here, we review the nano/microstructural effects on optical, thermal, and mechanical properties of polycrystalline ceramics, recent developments in a variety of commonly used crystalline laser materials, and potential future directions for more robust laser gain materials for high-power applications. It is argued that the engineering microstructure with both optical and thermal performances in mind might offer breakthrough improvements in laser gain media.

High-Pressure Investigation of 2,4,6-Trinitro-3-bromoanisole (TNBA): Structural Determination and Piezochromism

Understanding phase transitions in energetic materials is crucial for developing predictive models of detonation. 2,4,6-Trinitro-3-bromoanisole (TNBA), an energetic material, was studied in its single-crystal form up to pressures of 45 GPa in a diamond anvil cell. The material was characterized by using X-ray, Raman, and optical transmission measurements. From single-crystal X-ray diffraction, the ambient structure of TNBA was determined which crystallizes in the P21/c space group having four molecular units per unit cell. The X-ray data up to 9.2 GPa were fitted to a third-order Birch–Murnaghan equation of state by using the parameters K0 = 13.2(2.4) GPa and Kp = 5.1(1.4). Between 6.8 and 7.3 GPa, a phase transition was inferred in TNBA from concurrent fading of X-ray diffraction, disappearance of Raman peaks, increase in sample fluorescence, and discontinuous color change. The new phase was consistent with an amorphous state of at least partially intact molecules judging from the presence of higher-order Raman modes and irreversibility of the Raman spectra upon release. Piezochromism was observed with the translucent yellow TNBA gradually darkening and becoming opaque black at ∼25 GPa. This correlated to the absorption edge gradually shifting to the red in the visible spectrum. Signs of two possible additional structural transitions were detected in the 32.4–41.0 GPa range as suggested by a jump in the absorption edge, the irreversible changes in the absorption spectrum upon release to ambient pressure, and by the lack of Raman modes in recovered samples. The crystal and electronic structures of TNBA were also investigated up to 10 GPa by using DFT calculations and crystal structure prediction (CSP) simulations. In agreement with the experimentally observed transition at 7 GPa, the simulations at 10 GPa found a bevy of polymorphs lower in enthalpy and higher in density than P21/c. The lowest calculated enthalpy structure was determined to be P212121, being in a different space group than the ambient experimental result.

Copper(I) halide complexes with n,n’-diallylthiomorpholinium chloride: synthesis and crystal structure

By means of alternating current electrochemical technique, basing on ethanolic solutions of CuCl 2 ·2H 2 O or CuBr 2 and N,N’-diallylthiomorpholinium chloride, the two isostructural s-complexes of [C 4 H 8 NS(C 3 H 5 ) 2 Cu Hal 2 ] composition were obtained in a single crystal form and characterized by X-ray single crystal method: sp. gr. P 2 1 / c , Z = 4, Hal = Cl ( І ) – a = 7.7763(4), b = 13.1892(5), c = 13.1761(6) Å, β = 103.470(5)°, V = 1314.2(1) Å 3 , r calc. = 1.611 g/сm 3 , m (MoK a ) = 2.20 mm −1 , q max. = 28.8°, 10141 measured, 2659 used reflections, R ( F 2 ) = 0.032, S = 1.07; Hal = 1,04Br/0,96Cl ( ІІ ) – a = 7.9771(3), b = 13.2391(5), c = 13.1422(5) Å, β = 103.942(4), V = 1347.1(1) Å 3 , r calc. = 1.80 g/см 3 , m (MoK a ) = 5.02 mm −1 , q max. = 29.0°, 21269 measured, 2772 used reflections, R ( F 2 ) = 0.027, S = 1.08. In the crystal structure of the studied compounds, the trigonal-pyramidal coordination environment of Cu(I) includes sulfur atoms of the organic cation and three chloride anions (compound I ) or chloride/bromide mixture (compound II ). Atoms occupying position Hal (2) perform a bridging function and connect individual coordination polyhedrons into dimeric topological units {L 2 Cu 2 Hal 4 }. These dimers through hydrogen bonding are linked into a three-dimensional framework. None of the available allylic groups of the N,N’-diallylthiomorpholinium cation are coordinated to the copper(I) ion. In our opinion, this feature of the discussed crystal structure of [(C 4 H 8 NS(C 3 H 5 ) 2 )Cu Hal 2 ] compounds is explained by the influence of competition between the sulfur atom and the C=C bond of the allyl group of the cation during complexation in solution and the redistribution of electron density in the crystal structure of solid compounds due to hydrogen contacts C–H… Hal . Keywords : N,N’-diallylthiomorpholinium; copper(І); s-complexes; crystal structure.

Lithium-ion diffusion in the grain boundary of polycrystalline solid electrolyte Li6.75La3Zr1.5Ta0.5O12 (LLZTO): a computer simulation and theoretical study.

Lithium-ion diffusion ability in solid electrolytes is crucial for the performance and safety of lithium-ion batteries. However, the lithium-ion diffusion coefficient of Li6.75La3Zr1.5Ta0.5O12 (LLZTO) measured experimentally is much lower than that simulated theoretically because LLZTO exists widely in the polycrystalline form rather than in the single-crystal form. Herein, we focus on the construction of grain boundaries in polycrystalline materials to address this key issue. An amorphous structure is created by randomly throwing atoms into a virtual box, where the chemical bonds are broken and rearranged through continuous heating and annealing operations, resulting in a stable framework structure. The lithium-ion diffusion coefficients of polycrystalline LLZTO and single-crystal LLZTO calculated via Ab initio molecular dynamics (AIMD) are consistent with the experimental data in trend. Furthermore, the analysis of the grain boundary composed of the secondary phase in polycrystalline LLZTO reveals that the continuous -O-M-O- metal oxide grid with low formation energy per atom restricts the lithium-ion migration. The lithium-ion migration barriers calculated utilizing density functional theory (DFT) also demonstrate the obstacle of the grain boundary from another perspective.

Rubrene single crystal solar cells and the effect of crystallinity on interfacial recombination.

Single crystal studies provide a better understanding of the basic properties of organic photovoltaic devices. Therefore, in this work, rubrene single crystals with a thickness of 250 nm to 1000 nm were used to produce an inverted bilayer organic solar cell. Subsequently, polycrystalline rubrene (orthorhombic, triclinic) and amorphous bilayer solar cells of the same thickness as single crystals were studied to make comparisons across platforms. To investigate how single crystal, polycrystalline (triclinic-orthorhombic) and amorphous forms alter the charge carrier recombination mechanism at the rubrene/PCBM interface, light intensity measurements were carried out. The light intensity dependency of the JSC, VOC and FF parameters in organic solar cells with different forms of rubrene was determined. Monomolecular (Shockley Read Hall) recombination is observed in devices employing amorphous and polycrystalline rubrene in addition to bimolecular recombination, whereas the single crystal device is weakly affected by trap assisted SRH recombination due to reduced trap states at the donor acceptor interface. To date, the proposed work is the only systematic study examining transport and interface recombination mechanisms in organic solar cells produced by different structure forms of rubrene.

Local structural study of α-MoO3 micro-strips using synchrotron X-ray diffraction and X-ray Absorption Spectroscopy at Mo K-edge

The orthorhombic MoO3 micro-strips sample was synthesized using microwave assisted chemical co-precipitation technique. Synchrotron X-ray Diffraction (SXRD) pattern and Rietveld Refinement was used to estimate structural parameter, crystallite size of sample. It reveals that the synthesized sample MoO3 crystallized as an orthorhombic phase. X-ray Absorption Spectroscopy (XAS) measurement, which comprises both X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques, have been carried out on Mo K-edge to probe the local structure of samples. Local structure is also confirmed from the SXRD and Raman spectra of sample. XAS measurement reveals that the first bond length of Mo-O and Mo-Mo is 1.69 and 3.42 Å in orthorhombic MoO3 respectively. Transmission electron microscopy and SAED patterns showed stripe-like structure and single-crystal formation of MoO3 respectively.