Crystal Research and Technology最新文献

2D hexagonal boron nitride (h-BN), which has a similar honeycomb lattice structure to graphene, is a promising dielectric material for a wide variety of applications. Herein, the growth of high-quality and large-size multilayer h-BN crystals on Cu foils is reported by chemical vapor deposition (CVD) at atmospheric pressure. The size of an individual isolated hexagonal crystal of h-BN is about 20 µm, and the thickness is 3 nm. This paper studies the variables that affect h-BN growth during the process and the microstructure changes during the growth. Through analysis of the thermal and dynamic processes of chemical vapor deposition, relationships are derived between the mass of h-BN grown in the gas phase and various temperature and pressure factors. This information is used to develop appropriate parameters for commercial copper foil growth. Finally, using optimized conditions, high-quality h-BN at high pressure and low gas flow conditions are grown.

Glycinium oxalate (GO) and Bis(glycinium) oxalate (BGO) crystals are successfully grown using the slow evaporation solution growth technique. Following their growth, the crystals are subjected to a series of acoustic shock pulses. The effects of these shock pulses on the structural, optical, dielectric, and morphological properties of the crystals are comprehensively analyzed using various characterization techniques, including powder X-ray diffraction (XRD), UV-Visible spectroscopy, dielectric spectroscopy, and optical microscopy. Structural analysis through XRD reveals shifts in diffraction peak positions, indicating structural deformations. Fourier transform infrared spectroscopy analysis assesses the chemical stability of GO and BGO under shocked conditions. UV-Visible spectroscopy shows alterations in optical transmission with successive shock pulses, attributed to structural and surface defects. Dielectric properties are investigated over a frequency range from 1 Hz to 1 MHz, revealing variations in dielectric constant and loss tangent, which provide insights into the electrical behavior of the materials under normal and shocked conditions. Optical and scanning electron microscopy examine surface morphology, visualizing defects induced by the shock pulses. This study highlights the significant impact of shock pulses on the structural properties, optical transmission, dielectric properties, and surface morphology of GO and BGO crystals, offering valuable information on their resilience under dynamic conditions and potential applications.

Tetrahedral oxygenated groups with large highest occupied molecular orbital-lowest unoccupied molecular orbital (H gaps such as [SO₄] are beneficial for deep ultraviolet (DUV) transmission but usually make against generating sufficient birefringence due to the small polarizability anisotropy. Thus, it is extremely difficult to obtain DUV transmission and large birefringence simultaneously in the search for DUV birefringent materials in sulfates. Herein, two new ammonium-rare earth metal sulfates, NH₄Y(SO₄)₂·H₂O and NH₄YSO₄F₂, with DUV transmission are presented. Meanwhile, both exhibit greatly elevated birefringence through the involvement of NH₄⁺ units, compared to Y₂(SO₄)₃·8H₂O. Their optical properties are further investigated by theoretical calculations, and the effect of the introduction of NH₄⁺ into yttrium sulfate on optimizing the structures and properties is discussed. This work may provide a new perspective for further exploration of DUV birefringent materials in tetrahedral oxygenated group sulfates.

Potassium alunite is a potential mineral resource of potassium and aluminum that can serve as a valuable resource. An effective potassium and aluminum recovery method is developed using gradient leaching with a KOH sub-molten salt. The key part of this process is seeded precipitation of the potassium aluminate leach solution. Therefore, this study aims to optimize the seeded precipitation process by investigating the effects of alkali concentration, molecular ratio, stirring rate, temperature, and seed coefficient on the precipitation ratio and particle size of Al(OH)₃. The results show that alkali concentration, molecular ratio, temperature, and seed coefficient are key factors influencing seeded precipitation. Furthermore, the process is optimized by using these four identified factors as variables. A 9L(34) orthogonal experiment determines optimal conditions for maximizing the precipitation ratio and achieves the desired average particle size. Under the optimal condition of 200 g L⁻¹ alkali concentration, 1.5 molecular ratio, 1.0 seed coefficient, and 343.15 K temperature, the precipitation ratio reaches 54% and the average Al(OH)₃ particle size is 114 µm. Further work is required to scale up this optimized seeded precipitation process and evaluate applications of the Al(OH)₃ product.

The low-dimensional organic-inorganic lead halide compound has garnered significant attention in recent times due to its exceptional optoelectronic properties. However, its application in the field of optoelectronics has been hindered by the toxicity of lead. Here, a novel inorganic-organic compound [Epy]₂[CuBr₃] single crystal material with a 0D structure based on Cu(I) is introduced. The single crystal exhibits a broad band yellow luminescence, a significant Stokes shift, and a microsecond-scale photoluminescence (PL) lifetime, which is mainly attributed to the self-trapped excitons (STEs) excitation. In addition, the relevant PL spectra are measured at 78–348 K. The photoluminescence intensity decreases with increasing temperature due to strong electro-phonon coupling. The exciton binding energy E_b of the crystal is 76.43 meV, and the Huang-Rhys factor S is 40.55. It is worth noting that the crystal also shows a good response to X-rays. Overall, [Epy]₂[CuBr₃] displays its good potential.

Cover image provided courtesy of Jianguang Zhou, Research Center for Analytical Instrumentation, Institute of Cyber-Systems and Control, State Key Laboratory of Industrial Control Technology, Zhejiang University, China.

Oiling-out is a common phenomenon in industrial crystallization processes that not only prolongs the total operating time but also leads to undesirable crystal morphology, making it challenging to control crystallization paths. This review provides a comprehensive overview of the oiling-out phenomenon in organic small molecule crystallization. First, the formation mechanisms of oiling-out are summarized from both thermodynamic and dynamic perspectives, providing the theoretical foundation for understanding the phenomenon. Then, the universal characterization methods for studying the oiling-out phenomenon of organic small molecules are introduced in detail, covering both offline and online analytical tools. Moreover, the regulation strategy for oiling-out, including solvents, impurities, seeding, temperature, and mixing methods are discussed. This paper also focuses on the application of oiling-out in co-assembly and crystal shape modulation. Finally, future opportunities and challenges are presented to address the current shortcomings and application bottlenecks in the study of organic small molecule oiling-out phenomena. This review aims to provide valuable insights and guidance for researchers working on the crystallization of organic small molecules, particularly in the pharmaceutical industry, to better understand, control, and utilize the oiling-out phenomenon.

Recent observations of crystallization by thermal chemical vapor deposition systems indicate that the classical mechanism of nucleation and growth is followed. Information on aragonite nanocrystal growth and formation on substrate have been lacking due to the lack of reports on diffusional growth that can observe calcium carbonate nucleation processes in thin film formation. This report is important due to the additive-free method able to grow stable single-phase nanocrystals without the presence of other phases, amorphous or impurities. This work demonstrates homogeneous nucleation occurred in gas phase reaction in a constant flow of carbon dioxide gas (100 sccm) with optimally 0.5 M calcium chloride precursor in atmospheric pressure at 400 °C resulting in a calculated crystallite size of 27.8 nm. X-ray diffraction and energy dispersive spectrometer confirm the presence of calcium carbonate nanocrystal, whereas its structural changes are observed by its micrograph from field emission scanning electron microscope. The aim is to convey its importance in gaining control of aragonite nanocrystal morphology and structural properties, and thus generate nanocrystals with controlled phase. This work may contribute to development of more sensitive and crucial applications of calcium carbonate nanocrystal thin film such as in biosensors and biomedical.