Crystal Growth & Design最新文献

KSrY(BO₃)₂: Tb³⁺ and Tb⁴⁺ solid solutions have been obtained using the solid-state synthesis and top-seeded solution growth method from the KF flux. Comparing the two types of Tb spectra 3d_3/2 TbO₂ (Tb⁴⁺) and Na₃Tb(BO₃)₂ (Tb³⁺) with annealing in air of the KSrTb(BO₃)₂ crystal, X-ray photoelectron spectroscopy (XPS) revealed that the crystal contains about 15% of Tb⁴⁺. The entire Y/Tb series has polymorphic phase transitions that occur at temperatures between 550 and 600 °C. Synthesis and subsequent treatment methodology have an impact on the resulting Tb³⁺/Tb⁴⁺ ratio in the sample. The best luminescent properties were measured on the composition KSrY_0.9Tb_0.1(BO₃)₂, which was annealed at 700 °C under a hydrogen flow and cooled slowly.

Developing a crystallization model that accurately predicts crystal growth and nucleation has been an important topic in the pharmaceutical industry for the past few decades. Particularly, as the pharmaceutical industry shifts toward continuous manufacturing, modeling will both reduce the workload for experimental optimization and allow for the development of model-based control systems that yield more consistent quality output. In this work, a unique approach for modeling size-dependent growth was applied to a set of batch cooling crystallizations. The cooling crystallization of carbamazepine (CBZ) in ethanol was monitored for solute concentration measurement by in-line Raman spectroscopy as well as for seed and product crystal size distribution (CSD) measurement by off-line laser diffraction. Based on these data, modeling was performed with MATLAB software using a combined quadrature method of moments and a method of characteristics technique in conjunction with a modified Mydlarz and Jones (MJ3) expression for size-dependent growth. This work expands upon our past work on modeling the cooling crystallization of CBZ by evaluating the effect of variable seed CSD on crystal growth rates as well as the accuracy of the model-predicted product CSD. Using the MJ3 size-dependent growth expression, variation in seed CSD resulted in high prediction errors for product CSD especially for the D10 value [root-mean-square error (RMSE) = 29.8%]. The error was reduced by varying the size-dependent growth parameters as a function of the seed CSD (RMSE = 7.4%). This new technique provided a better understanding of how the overall CSD affects crystal growth rates. The improved model may reduce the time needed to optimize experiments and provide better control of the variation of the CSD of the system.

Silicon carbide (SiC) single crystals are ideal platforms for fabrication of high-voltage, high-frequency, and high-temperature application devices, showing great potential applications in electric vehicles, photovoltaics, and rail transit. Among SiC-based devices, n-channel insulated gate bipolar transistors (IGBTs) show superior performances. However, their developments remain stagnant, predominantly ascribed to the lack of wafer-scale p-type SiC single crystals. Here, we report the breakthrough in the growth of 4-inch p-type 4H-SiC single crystals from high-temperature solutions with high crystalline quality and uniform doping. The average full width at half-maximum for the (0004) plane X-ray rocking curve is 19.4 arcsec and the resistivity deviation along the thickness direction is only 7.89%, outperforming those of the reported p-type SiC single crystals. The density of dislocation etching pits is 888.89 cm^–2. The size of the dislocation etching pits is 1/10th of its counterpart grown by the physical vapor transport technique. The quality improvement is due to the removal of voids induced by gas bubbles, alongside the improvement of other growth parameters. The growth of wafer-scale p-type SiC opens a gate to the fabrication of n-channel SiC-based devices like n-IGBTs.

With the characteristic two-dimensional (2D) electronic structure of 1,3,6,8-tetrakis(methylthio)pyrene (MT-pyrene), affording ultrahigh mobility on single-crystal field-effect transistors, we expected MT-pyrene to be a promising platform for highly conducting 2D metallic molecular conductors. To address this, we carried out electrochemical crystallization of MT-pyrene to obtain a series of conducting radical cation salts. Although some salts were highly conducting and showed metallic behavior at around room temperature, they became insulating at low temperatures. These conducting behaviors are consistent with their one-dimensional nature, which originates in the molecular arrangement in the solid state and the distribution of the HOMO in the MT-pyrene molecule.

Organic–inorganic hybrid ferroelastic materials have emerged as promising candidates for various applications such as mechanical switches, signal conversions, and memory materials because of their convenient processing, structural flexibility, and environmental friendliness. Here, we reported a supramolecular assembly hybrid perovskite (15-crown-5·NH₄)₂TeCl₆ (1) semiconductor containing stator ammonium and rotor 15-crown-5 as cations and TeCl₆ as an anionic part. This hybrid perovskite shows a ferroelastic phase transition and dielectric switch induced by the motions of the crown rotor. In addition, it shows an X-ray detection response with a clear switching ratio of photocurrent 0.011 and dark current 0.001 nA cm^–2. This study reveals the advantages of a supramolecular rotor strategy in discovering novel molecular ferroelastic semiconductor materials and provides a new avenue to explore functional hybrid molecular materials.

Environmental-friendly spherical crystallization technology has always been the focus in the field of crystallization. In this work, a novel crystal self-bridging (CSB) mechanism is proposed. In the absence of additives and organic solvents, preliminary agglomeration is generated through the adhesion force between crystals, and stable agglomeration is formed by the solid-bridge generated by crystal growth. The mechanism was explained from the perspective of the adhesion free energy. Myo-inositol (MI) was selected as the research object, and then a spherical agglomeration process was developed based on the CSB mechanism. Based on detailed experiments, we found that the seed size should be smaller than 100 μm (150 mesh). In addition, the optimal supersaturation ratio and suspension density should be 1.25 and 80 kg/m³, respectively. A fluidized bed crystallizer was used to enhance the crystallization process. Strategies of particle size control were proposed, and prediction equations for particle size were provided. The obtained spherical MI was compared with powdered and flaky MI, and then it was demonstrated that the spherical MI was excellent in terms of morphology, particle size distribution, flowability indicators, anticaking performance, and dissolution rate. The spherical particles of choline tartrate, niacinamide, and vitamin B1 were successfully prepared according to a CSB mechanism, so the universality of this mechanism was demonstrated. The results of this work provide effective guidance for improving the particle size and powder properties of MI and contribute to the promotion of the CSB mechanism to other systems.

Vanadium dioxide (VO₂) films, which undergo a metal–insulator transition (MIT) at 68 °C, are promising materials for switching device applications. Topotactic oxidation of vanadium sesquioxide (V₂O₃) epitaxial films yields highly oriented VO₂ films. However, the effect of oxidation conditions on the MIT properties of the resulting VO₂ films has not been thoroughly explored. In this study, we investigated the effects of oxidation conditions, such as oxygen partial pressure, temperature, and time, on the topotactic transformation from V₂O₃ to VO₂ films and fabricated high-quality VO₂ films. Thermodynamic calculations demonstrated that oxidation atmospheres with thermodynamically stable VO₂ can be formed using a gas mixture containing water vapor and hydrogen. Experiments with different oxidation parameters revealed that the optimal oxidation conditions are oxygen partial pressures ranging from 10^–20 to 10^–8 atm, oxidation temperature of 500 °C, and oxidation times exceeding 6 h. Under these conditions, V₂O₃ was topotactically oxidized to VO₂, and the electrical resistance of the resulting VO₂ films changed by 4.7 orders of magnitude across the MIT. This study opens new avenues for fabricating highly sensitive VO₂-based switching devices.

The cocrystallization of active pharmaceutical ingredients (APIs) is known to be a technique suitable for overcoming certain physicochemical issues concerning the solid forms of drugs. In the case of the cocrystal of 5-fluorocytosine and isoniazid, two widely used active pharmaceutical ingredients, for example, the cocrystallization improved the phase stability of the latter against moisture, thus increasing its shelf life. The room-temperature crystal structure was already reported in the literature, but no charge density study has been published so far. To further evaluate the structural properties of this potential codrug, which is stabilized by a supramolecular synthon containing N–H···N-type hydrogen bonds, here we performed the experimental and theoretical charge density analyses of the drug–drug cocrystal formed by the antimetabolite prodrug 5-fluorocytosine and the tuberculostatic drug isoniazid. Topological analyses were also performed for all models and compared, indicating a good agreement between experiment and theory. The comparison with gas-phase calculations enabled the evaluation of the charge redistribution upon cocrystallization as well as the effect of the intermolecular interactions. In this manner, it was possible to evaluate the variations in bond distances and electron densities at the bonds involved in the intermolecular heterosynthon. Through the total charge of each molecule in the cocrystal, it was also possible to have insights into the charge redistribution when both molecules crystallize together. Electrostatic potential maps were also calculated for the experimental data and compared with the gas-phase calculations.

Experimental and theoretical charge density and topological analyses are performed on a codrug of isoniazid and 5-fluorocytosine. Results allow the classification of intermolecular interactions and the evaluation of the charge redistribution on the molecules upon cocrystallization.

To further enhance the hydrogen evolution activity of g-C₃N₄, Au nanoparticle (NP)-modified defective-state g-C₃N₄ nanosheet photocatalysts (Au/HCN) were successfully prepared through in situ photodeposition in this study. The prepared Au/HCN exhibited an excellent photocatalytic hydrogen evolution activity. Under full spectrum, the hydrogen production rate of Au/HCN (7289 μmol·g^–1·h^–1) was 1.6 times higher than that of Au NPs-modified pure g-C₃N₄ nanosheets (Au/CN) (4437 μmol·g^–1·h^–1) and 4.3 times higher than that of Au NPs-modified bulk g-C₃N₄ (Au/BCN) (1664 μmol·g^–1·h^–1). The photoluminescence and steady-state photovoltage spectra indicate that Au/HCN has the highest ability for photogenerated charge separation and photogenerated electron transfer efficiency. The ultraviolet–visible spectrophotometer (DRS) spectra revealed an additional light absorption peak at 520 nm for Au/HCN. The above results indicate that the defects can effectively inhibit the recombination of photogenerated charges from HCN. In addition, the synergistic interaction between Au NPs and HCN, as well as the surface plasmon resonance effect of Au NPs, promoted photocatalytic hydrogen evolution.

Endowing luminescent crystals with adjustable mechanical flexibility and rigidity is a challenge. In this work, we successfully achieve water-vapor-regulated mechanical and luminescent properties in a single system based on a novel ethoxy-substituted cyanostilbene derivative (DEA). Specifically, the pristine crystal of DEA exhibits elasticity with a yellow fluorescence. Upon water-assisted vapor fuming, a rigid crystal (DEA-w) with an orange fluorescence was obtained. The analysis of crystal structures shows that water can form multiple hydrogen bonds with the DEA molecule, further compelling the whole packing structure (crystal-to-crystal) transformation. Experimental and theoretical investigations reveal that the red-shifted fluorescence is ascribed to the enhanced intermolecular overlap, which favors an excimer emission. The “soft-to-rigid” transition is attributed to the packing transformation from a one-dimensional π column to a two-dimensional strong hydrogen bond network, which provides stronger resistance to external deformation. In addition, the DEA-w crystal undergoes a typical brittle fracture under cutting, offering excellent processability. This study provides an inspired method for in situ adjustment of the mechanical properties of the crystal.