Single Crystalline Form Research Articles

Non-isothermal crystallization kinetics and its effect on the mechanical properties of homopolymer isotactic polypropylene

The non-isothermal crystallization of the isotactic Polypropylene (iPP) was studied using differential scanning calorimetry and polarizing optical microscopy. Jeziorny’s model and Ozawa’s theoretical approaches were applied to study the non-isothermal kinetics of the iPP. Jeziorny’s approach proved to be the most relevant model to the present material. Simultaneously, the activation energy was calculated with Kissinger’s method and Vyazovkin’s iso-conversional approach. Indeed, the latter provides an activation energy varying between 100 and 176 kJ/mol. Furthermore, the WAXD scans indicated the presence of a single crystalline form in the used material. To study the effect of the microstructure on the mechanical properties of the iPP, multiscale tensile tests were carried out for different film microstructures. At macroscopic scale, the increase in the diameter of spherulites, inevitably accompanied by a rise in the crystallinity rate, induces the growth of rigidity, brittleness, and elastic limit. Moreover, the results of the in-situ micro-tensile tests present the evolution of spherulites during loading.

Synthesis, characterization and antioxidant activities of some novel oxime derivatives

In this study, nine novel compounds were synthesized in the reaction of ω-chloroisonitrosoacetophenone with 2-chloro-4-methylaniline, 2-chloro-5-methylaniline, 2-chloro-6-methylaniline, 3-chloro-2-methylaniline, 4-chloro-3-methylaniline, 5-chloro2-methylaniline, 2,3-dichloroaniline, 2,4-dichloroaniline and 3,5-dichloroaniline resulting for C1-C9, respectively. Compounds C1, C4-C7 and C9 were handled in single crystalline forms, which the structures were also investigated by X-ray single crystal analysis. Compounds were evaluated for their nonenzymatic lipid peroxidation inhibition, antioxidant and antiradical activities and compared with standard agents at 5, 50, and 100μM concentrations. Compounds are exhibited good antioxidant activities and lipid peroxidation compared to standards (BHA, TBHQ, BHT and trolox). Due to the best of our knowledge for novel oxime compounds, this study is the first report of promising antioxidants to scavenge oxidative stress conditions.

Quantum spin state transitions in the spin-1 equilateral triangular lattice antiferromagnet Na2BaNi(PO4)2

We have grown single crystals of Na$_2$BaNi(PO$_4$)$_2$, a new spin-1 equilateral triangular lattice antiferromagnet (ETLAF), and performed magnetic susceptibility, specific heat and thermal conductivity measurements at ultralow temperatures. The main results are (i) at zero magnetic field, Na$_2$BaNi(PO$_4$)$_2$ exhibits a magnetic ordering at 430 mK with a weak ferromagnetic moment along the $c$ axis. This suggests a canted 120$^\circ$ spin structure, which is in a plane including the crystallographic $c$ axis due to the existence of an easy-axis anisotropy and ferromagnetically stacked along the $c$ axis; (ii) with increasing field along the $c$ axis, a 1/3 magnetization plateau is observed which means the canted 120$^\circ$ spin structure is transformed to a up up down (UUD) spin structure. With even higher fields, the UUD phase further evolves to possible V and V' phases; (iii) with increasing field along the $a$ axis, the canted 120$^\circ$ spin structure is possibly transformed to a umbrella phase and a V phase. Therefore, Na$_2$BaNi(PO$_4$)$_2$ is a rare example of spin-1 ETLAF with single crystalline form to exhibit easy-axis spin anisotropy and series of quantum spin state transitions.

Highly flexible CH3NH3PbI3 micro- and nanowires

CH3NH3PbI3 is known to be very efficient in photon to electron conversion, which makes it extremely popular in opto-electronic applications ranging from solar cells to photodetectors. The material is very brittle in bulk, single crystalline, and thin film forms. Here, we report a high flexibility of it in micro- and nanowires' (marked as NWs) shapes contrary to thin films. This result represents an important step toward applications of this highly performant perovskite in flexible optoelectronic devices. The great suppleness originates from the highly crystalline form of these NWs.

Solubility behaviors of (Na+, K+or NH4+)hexafluoridosilicates in H2SO4, HF, H2SiF6, H3PO4 acidic aqueous solutions at T=353.15 K

The solubility equilibria of sodium, potassium or ammonium hexafluoridosilicates in hydrofluoric, sulfuric, hexafluoridosilicic, and phosphoric acids aqueous solutions were investigated at T=353.15 K. The experimental solubilities were performed at various molalities ranging from dilution to concentrated solutions of acid. The dissolution of these salts in acidic solutions could be one of the solutions to overcome the problem of fouling during the production of phosphoric acid. The knowledge of the behaviors and solid-liquid equilibria of these compounds in acid aqueous solutions is essential to understand the mechanisms governing such complex thermodynamic equilibria in phosphate industry. The formed solid phases of (Na+,K+,orNH4+) hexafluoridosilicates were characterized using X-ray diffraction and IR spectroscopy. The obtained solids show only a single crystalline form corresponds to malladrite, hieratite, or cryptohalite respectively. The solubility behaviors of these compounds in acidic aqueous solutions are different over the molality range of each acid. The exact treatments of these systems can be complicated according their trends. They may be different from that expected and it's depending on the molality range of acid (pH) and species in solutions at temperature 353.15K.

Simple and effective purification of a SGLT-2 inhibitor cocrystal Rongliflozin l-pyroglutamic acid: coformer-induced purification

We report and design a simple and robust process to obtain a single and pure crystalline form I (1) of the cocrystal, containing Rongliflozin (2) with l-pyroglutamic acid (l-PA), based on coformer-induced purification (CoIP).

Bi-templated grain growth maximizing the effects of texture on piezoelectricity

Templated grain growth is beneficial for piezoelectric materials, the properties of which become the best in their single crystalline form. Nevertheless, a textured ceramic prepared by a templated grain growth technique often fails in exhibiting as good properties as expected in single crystals even with a high degree of orientation factor. Here, we propose a new strategy for maximizing texturing effect by suppressing the growth of untextured matrix grains. The textured ceramics made by our method, so-called bi-templated grain growth, are featured by ultrahigh piezoelectric properties (d33 = ∼1,031 pC/N, d⋅g = ∼59,000, kp = ∼0.76). A special emphasis is on the achieved electric-field-induced strain of 0.13 % at 1 kV/mm, which is as high as that of single crystals. This work demonstrates that not only the degree of texture but also the coarsening of untextured matrix grains should be well-controlled to best exploit the templated grain growth technique.

Electric and Photoelectrochemical Properties of CuGaSe2 Single Crystal

The CuGaSe2 compound is a promising material as a photoabsorber of solar cell due to its p-type semiconductive characteristic and optimum band gap for sunlight absorption (1.68 eV). This compound is also attractive for the use of a photocathode for photoelectrochemical (PEC) water splitting because of its sufficient negative energy level of conduction band minimum (CBM) to induce reduction of water. For such applications, a thin-film form of the compound is usually used. In order to clarify and control its bulk and/or surface properties optimal for photovoltaic and PEC applications, we attempted to use a single crystalline form of the compound obtained by using a conventional vertical Bridgman technique.Several crystallographic and compositional analyses indicated successful formation of the CuGaSe2 single crystal. Electronic properties of the thus-obtained single crystal measured after processing into a wafer form suggested a p-type semiconductive characteristic responsible for the use of photocathode. However, due to the insufficient acceptor concentration, the PEC property of the sample was not enough as was expecting it to be. After various trial, post annealing in a Se vapor atmosphere was found to be effective for improvement of its PEC functions. Details on effects of the annealing on the photovoltaic and the PEC hydrogen evolution properties were examined.

Discovery and Single Crystal Growth of High Entropy Pyrochlores.

A family of high entropy oxides with the formula Mg2Ta3Ln3O14 (Ln = La, Pr, Nd, Sm, Eu, Gd) has been discovered and synthesized. Single crystals, 5 mm OD × 2.5 cm, for Ln = Nd have been grown using the laser optical floating zone technique. Crystal orientations are confirmed by Laue diffraction, and structure solutions were obtained via single crystal X-ray diffraction. The structure is found to be a partially disordered pyrochlore, space group Fd-3m, fractional chemical formula (Mg0.25Nd0.75)2(Mg0.25Ta0.75)2O7. Magnetization measurements indicate ordinary paramagnetic behavior in all compounds down to T = 2 K, except in the Eu variant which possesses Van Vleck paramagnetism. Specific heat measurements for Ln = Nd shows no phase transitions between T = 300 and 2 K. We demonstrate the ability to prepare magnetically disordered materials by substitution of Mg with Ni, Mn, and Co, demonstrating the flexibility of this family in accommodating defects. The stabilization of these compounds could be due to the entropy gain associated with defects, showcasing a "materials by design" approach by using disorder to stabilize novel magnetic and optical materials. Our work also demonstrates the feasibility of preparing high entropy oxides in single crystalline form.

Scalable Fabrication of Molybdenum Disulfide Nanostructures and their Assembly.

Molybdenum disulfide (MoS2 ) is a multifunctional material that can be used for various applications. In the single-crystalline form, MoS2 shows superior electronic properties. It is also an exceptionally useful nanomaterial in its polycrystalline form with applications in catalysis, energy storage, water treatment, and gas sensing. Here, the scalable fabrication of longitudinal MoS2 nanostructures, i.e., nanoribbons, and their oxide hybrids with tunable dimensions in a rational and well-reproducible fashion, is reported. The nanoribbons, obtained at different reaction stages, that is, MoO3 , MoS2 /MoO2 hybrid, and MoS2 , are fully characterized. The growth method presented herein has a high yield and is particularly robust. The MoS2 nanoribbons can readily be removed from its substrate and dispersed in solution. It is shown that functionalized MoS2 nanoribbons can be manipulated in solution and assembled in controlled patterns and directly on microelectrodes with UV-click-chemistry. Owing to the high chemical purity and polycrystalline nature, the MoS2 nanostructures demonstrate rapid optoelectronic response to wavelengths from 450 to 750nm, and successfully remove mercury contaminants from water. The scalable fabrication and manipulation followed by light-directed assembly of MoS2 nanoribbons, and their unique properties, will be inspiring for device fabrication and applications of the transition metal dichalcogenides.

Conformational Solvatomorphism in a [2]Catenane

The combination of a flexible pyridine-appended ligand (L1) with 4,4′-bipyridine (L2) and cis-protected Pd(II) units, Pd(L′)(NO3)2, in water yielded a concentration-dependent equilibrium mixture of the corresponding [2]catenanes [Pd2(L′)2(L1)(L2)]2(NO3)8 and their constituent macrocycles [Pd2(L′)2(L1)(L2)](NO3)4. The cis-protecting units (L′) used were ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen). Crystallization of the [2]catenanes via slow evaporation of their CH3CN/H2O (1:1) solutions yielded a single crystalline form in the case of [Pd2(2,2′-bpy)2(L1)(L2)]2(NO3)8 and two concomitant crystalline forms (solvates) in the case of [Pd2(phen)2(L1)(L2)]2(NO3)8. The formation of the [2]catenane is facilitated by noncovalent interactions such as N–H···O, C–H···O, and C–H···π contacts and π···π stacking. The solvates of [Pd2(phen)2(L1)(L2)]2(NO3)8 revealed differences in the orientation of the amide carbonyl group and conformational differences in the ligands and phen units in the macrocycles and may thus be termed conformational solvatomorphs. The molecular packing in all the structures was found to be driven by intermolecular π···π stacking interactions between the aromatic rings in their cis-protected Pd(II) units. However, because of the awkward shape of the molecules, the closest 2,2′-bpy and phen units in all the structures overlap differently rather than the commonly observed “head-to-tail” or “head-to-head” modes.

Advances in High-Resolution Ultrafast LuI3:Ce Scintillators for Fast Timing Applications

Scintillation detectors exhibiting high spatial resolution and fast timing capabilities are of vital importance for synchrotron sources. These detectors may be exposed to a variety of X-ray energies (up to 140 keV) and used in high frame rate applications. Here, we describe the advances in the development of thin-film LuI3:Ce scintillators for higher energy X-ray imaging, with fast timing and high spatial resolution. When grown in a single crystalline form, these scintillators are bright, producing 115 000 photons/MeV. However, to achieve high spatial resolution, these scintillators are grown in thin-film form with a microcolumnar structure, controllable to column diameters of $30~\mu \text{m}$ . Thus, a much thicker scintillator layer ( $10~\mu \text{m}$ –3 mm or higher) may be grown, providing superior X-ray absorption while achieving high resolutions of $50~\mu \text{m}$ or better, at the cost of reduced light yield. To study the timing characteristics of the scintillator, time-resolved X-ray excited optical luminescence (TR-XEOL) was performed on two different sets of three samples of LuI3 at the 1-BM beamline of the Advanced Photon Source at Argonne National Laboratory. Besides, we report timing measurements obtained using a photomultiplier tube (PMT) and oscilloscope at Radiation Monitoring Devices (RMD) Inc. Using the TR-XEOL, we determined the decay constants of LuI3 as a function of Ce doping, recording a fast decay component as low as 3.6 ns (39%), one of the fastest values recorded in inorganic scintillators. This fast decay opens up numerous novel applications, where ultrahigh frame rates are important using synchrotron X-rays. This article will discuss fabrication, characterization, and potential applications for this novel scintillator.

Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co3O4 hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal-organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths-namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites-were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = -1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co3O4, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic performance in toluene oxidation, it achieved a toluene conversion of 90% (T90) at ∼227 °C (a space velocity of 60 000 mL g-1 h-1) and the activity energy (Ea) is 69.5 kJ mol-1. A series of characterizations were performed to investigate the structure-activity correlation. It was found that there are more structure defects, more adsorbed surface oxygen species, more surface Co3+ species, and higher reducibility at low temperatures on the Co-MeCN-O than on other Co3O4 samples; these factors are responsible for its excellent catalytic performance. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that, when there is no oxygen in the atmosphere, the lattice oxygen may be involved in the activation of toluene, and the gas-phase oxygen replenished by the oxygen vacancies was essential for the total oxidation of toluene on the surface of the Co-MeCN-O catalysts, it also proves the importance of oxygen vacancies. Moreover, for the Co-MeCN-O catalysts, no obvious decrease in catalytic performance was observed after 120 h at 220 °C and it is still stable after cycling tests, which indicates that it exhibits excellent stability for toluene oxidation. This study sheds lights on the controllable synthesis of macroporous-microporous materials in single-crystalline form without an external template, and, thus, it may serve as a reference for future design and synthesis of hollow porous materials with outstanding catalytic performance.

Charge-Separated Metal–Organic Frameworks Derived from Boron-Centered Tetrapods

Metal–organic frameworks (MOFs) are an emerging class of microporous materials that have potential applications in a wide range of areas. As a subclass of MOFs, ionic MOFs, especially charge-separated MOFs, have been relatively less studied but possess unique features including strong host–guest interactions from the exposed charged centers. We report the synthesis and single-crystal structural characterization of five new charge-separated MOFs (UNM 1–5) based on two tetrapodal borate ligands: tetrakis(4-(4-pyridineethynyl)-2,3,5,6-tetrafluorophenyl)borate (T1) and tetrakis(4-(4-pyridyl)-2,3,5,6-tetrafluorophenyl)borate (T2) having rigid arms of different lengths and pyridine groups at the end of each arm. Coordination of these tetrapods with Cu(I), Cu(II), and Ag(I) ions under specific conditions led to a series of new charge-separated MOFs in single crystalline forms. UNM-1 and UNM-2/UNM-3, which crystallize respectively in tetragonal I4̅ space group and monoclinic C2/c space group, are derived from Cu(CH3CN)4BF4 and Cu(NO3)2 upon coordination with T1. On the other hand, coordination of T2 with Cu(CH3CN)4BF4 and AgBF4 respectively yielded UNM-4 and UNM-5 in the monoclinic I2/a space group. All these MOFs possess several degrees of interpenetration that are correlated with the arm lengths of ligands. Noticeably, UNM-1 is 4-fold interpenetrated, leading to the highest stability among all five MOFs, while still displaying an impressive Brunauer–Emmett–Teller (BET) surface area (SABET) of ca. 621 m2/g. Our findings highlight the versatility of tetrapodal borate ligands in engineering charge-separated MOFs with diverse structures and controlled functionality.

Giant enhancement in coercivity of ferromagnetic α-Fe2O3 nanosheet grown on MoS2

To study the 2D materials, an interface interaction is very important to tune the physical properties because of the large specific surface area. When the antiferromagnetic α-Fe2O3 is grown in a single-crystalline form on a diamagnetic MoS2, enormous changes in magnetic properties are observed in the 2D composite system. Strong ferromagnetism with a giant coercivity of 1.8 T is observed in this single-crystalline α-Fe2O3/MoS2 heterostructure. It is noted that thinner sheets show better coercivity than the thicker sheets, and the coercivity decreases with the increase in temperature. This huge coercivity in larger and thinner single-crystalline α-Fe2O3 sheets grown on a MoS2 arises due to charge transfer from “S” to “Fe” and the surface pinning effect at the interface. A large negative magnetoresistance with a maximum value of 15% is achieved due to the spin-spin interaction, and a positive magnetoresistance is also observed at low field and high temperature as a result of the spin splitting effect.

Tuning the π-π overlap and charge transport in single crystals of an organic semiconductor via solvation and polymorphism.

Polymorphism is a central phenomenon in materials science that often results in important differences of the electronic properties of organic crystals due to slight variations in intermolecular distances and positions. Although a large number of π-conjugated organic compounds can grow as polymorphs, it is necessary to have at disposal a series of several polymorphs of the same molecule to establish clear and predictive structure-property relationships. We report here on the occurrence of two solvates and three polymorphs in single crystalline form of the organic p-type semiconductor 2,2',6,6'-tetraphenyldipyranylidene (DIPO). When grown from chlorobenzene or toluene, the DIPO crystals spontaneously capture solvent molecules to form two pseudopolymorphic 1 : 1 binary solvates. Independently, three solvent-free DIPO polymorphs are obtained either from the vapor phase or from acetonitrile and benzene. Surprisingly, single crystal field-effect transistors (SC-FETs) reveal that the DIPO 1 : 1 binary solvate grown from chlorobenzene possesses a higher hole mobility (1.1 cm2 V-1 s-1) than the three solvent-free polymorphs (0.02-0.64 cm2 V-1 s-1). A refined crystallographic analysis combined with a theoretical transport model clearly shows that the higher mobility of the solvate results from an improved π-π overlap. Our observations demonstrate that solvation allows to tune the π-π overlap and transport properties of organic semiconductors by selecting appropriate solvents.

Generation of complex magnetic phase diagram of single crystalline Sm0.50Ca0.25Sr0.25MnO3 compound using magnetocaloric effect

A detail study has been performed for the Sm0.50Ca0.25Sr0.25MnO3 compound in its single crystalline form. Distinctly different nature in their magnetocaloric responses (with temperature and external magnetic field variation) were found depending upon the direction of the external magnetic field. Additionally, we have constructed magnetic phase diagram from the magnetic and magnetocaloric effect. Different features in magnetic phase diagram were addressed considering the shape induced magnetic moments configuration in different orientation.

Pronounced 23 magnetization plateau in a frustrated S=1 isolated spin-triangle compound: Interplay between Heisenberg and biquadratic exchange interactions

We report the synthesis and characterization of a new quantum magnet [2-[Bis(2-hydroxybenzyl)aminomethyl]pyridine]Ni(II)-trimer (BHAP-Ni3) in single-crystalline form. Our combined experimental and theoretical investigations reveal an exotic spin state that stabilizes a robust 2/3 magnetization plateau between 7 and 20 T in an external magnetic field. AC-susceptibility measurements show the absence of any magnetic order/glassy state down to 60 mK. The magnetic ground state is disordered and specific-heat measurements reveal the gapped nature of the spin excitations. Most interestingly, our theoretical modeling suggests that the 2/3 magnetization plateau emerges due to the interplay between antiferromagnetic Heisenberg and biquadratic exchange interactions within nearly isolated spin $S$ = 1 triangles.

Structural, thermodynamic, thermal, and electron transport properties of single-crystalline LaPt2Si2

${\mathrm{LaPt}}_{2}{\mathrm{Si}}_{2}$ in a single-crystalline form was subjected to structure, thermodynamic, thermal, and electron transport studies with a special emphasis on the structure phase transition appearing at $T=85$ K. X-ray diffraction proves the noncentrosymmetric tetragonal structure of ${\mathrm{CaBe}}_{2}{\mathrm{Ge}}_{2}$-type (space group P4/nmm). The transition manifests as a small step of opposite sign in both lattice parameters, leaving almost no volume change. $c$ decreases and $a$ increases in the low-$T$ phase, but the change of the $c/a$ ratio does not exceed $0.1%$. Additional periodicity, related to the supposed charge density wave (CDW) state, can be related to satellites corresponding to the wave vector $q\ensuremath{\approx}(0.36,0,0)$, which start to grow with temperature decreasing below 175 K and almost vanish (or relocate from the investigated $ab$ plane) below the 85 K transition. Electrical resistivity reveals that the 85 K transition is hysteretic in temperature, with the difference between heating and cooling being almost 10 K, proving the first-order type of the transition. The transition dramatically enhances resistivity in the low-$T$ state, pointing to a formation of a pseudogap. This, however, does allow a superconducting state, arising below ${T}_{c}=1.6$ K. The temperature dependence up upper critical field is not compatible with the weak coupling BCS theory. Strong anisotropy of electronic structure and its dramatic changes at the structure transition are manifest also in thermal expansion and thermoelectric power. The Sommerfeld coefficient $\ensuremath{\gamma}=7.8\phantom{\rule{4pt}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$ and Debye temperature of 205 K could be derived at low temperatures, but the specific heat has a strongly non-Debye like $T$ dependence, which can be ascribed to a low-energy Einstein mode.

Solid dispersions of telaprevir with improved solubility prepared by co-milling: formulation, physicochemical characterization, and cytotoxicity evaluation.

Telaprevir (TVR) is typically a poorly soluble drug with an extremely low bioavailability of 1.7%. Polymorph modifications cannot improve the solubility of TVR because it only has a single unsolvated crystalline form. Co-crystals also provide limited bioavailability enhancement for TVR. Thus, in this study, we increased the solubility and dissolution rate of TVR through formulations of TVR-polymer solid dispersions. Three solid dispersions of TVR were successfully prepared by co-milling with polyvinylpyrrolidone K30 (PVP), polyethylene glycol 6000, and hydroxypropyl methylcellulose (HPMC), which were characterized by different techniques. According to X-ray powder diffraction and differential scanning calorimetry results, TVR presented in amorphous form in all solid dispersions. The fourier transform infrared spectra results indicated that TVR may connect with polymers through the N-H···O or O-H···O hydrogen bonds, which were verified by molecular docking. TVR-PVP and TVR-HPMC displayed a good stability at conventional RH levels, and their thermostabilities were better than those of milled TVR. Among the three solid dispersions, TVR-HPMC showed significant solubility and dissolution rate advantages in different media. Moreover, TVR-HPMC displayed the same anticancer efficacy with crystalline TVR and presented no toxic side effects to normal liver cells. Thus, TVR-HPMC showed potential application value.