Crystal Research and Technology最新文献

This work reports on the determination of the heat conductivity of high temperature stable carbon materials in the temperature range well above 2000 °C where classic material characterization methods fail. Dense graphite (DG) materials as well as rigid and soft felt isolation (RFI/SFI) components have been investigated which are used during crystal growth of SiC by the physical vapor transport method (PVT) in the temperature regime of 2000 and 2400 °C. The applied materials characterization methods include low temperature physical heat conductivity measurements using laser flash analysis (LFA) in the temperature range 25–1200 °C, data extrapolation to elevated temperatures up to 2400 °C, and a correlation of heating processes and computer simulation of the temperature field of different hot zone designs. Using this approach, the calculated temperatures and experimentally determined values with an error of less than ± 2% at 2400 °C can be merged.

In this study, semitransparent lead films serve as substrates for depositing niobium pentoxide thin films, forming versatile electro-optical devices. Using vacuum evaporation and ion sputtering techniques at ≈10⁻⁵ mbar, stacked layers of crystalline Pb and amorphous Nb₂O₅ are created. This process reduces free carrier absorption in Nb₂O₅ and forms Urbach tail states with a width of 0.91 eV. Pb/Nb₂O₅ thin films exhibit remarkable broadband absorption, exceeding 440% in the visible and 98% in the infrared. Moreover, Pb substrates induce a redshift in Nb₂O₅’s energy bandgap. Electrical analysis using impedance spectroscopy on Pb/Nb₂O₅/Ag structures reveals their series/parallel resonance and bandstop filter properties. Notably, the bandstop filters exhibit reflection coefficient minima at a notch frequency of 1.66 GHz, with a bandwidth of 280 MHz, return loss of 26 dB, and voltage standing wave ratio of 1.13. These findings underscore the device's potential for wide-ranging electro-optical applications across the electromagnetic spectrum.

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.

In order to explore the crystallization behavior of Co-doped amorphous manganese dioxide(Co-doped AMO) and to investigate the electrochemical properties of its different crystallization products as cathodes for aqueous zinc ion batteries. In this work, the effects of heat treatment temperature on the microstructure and phase composition of Co-doped AMO and their electrochemical properties of Zn-MnO₂ battery cathode materials are systematically investigated. The results show that Co-doping increases the crystallization temperature of pure AMO. When the heat treatment temperature is 400 °C, Co-doped AMO is amorphous. At 500 and 550 °C, part of the Co-doped AMO crystallizes into tetragonal spinel structured (Co, Mn)(Co, Mn)₂O₄ material between MnCo₂O₄ and Mn₃O₄. At 650 °C, the crystallized product is completely nano-α-Mn(Co)O₂ crystal. The maximum discharge specific capacities and the retention rate after 100 cycles of the samples at 100 mA g⁻¹ are 325.40 mAh g⁻¹, 86.88%; 217.00 mAh g⁻¹, 13.94%; 186.68 mAh g⁻¹, 41.01%; and 149.03 mAh g⁻¹, 31.27% for the unheated and 400, 550, 650 °C heat-treated samples, respectively. It is proved that the Co-doped AMO without heat treatment is superior to the partially or fully crystallized materials in terms of comprehensive performance and cost as cathode materials for AZIB.

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.