Properties Of Crystals Research Articles

Warm white-light emission from self-trapped excitons in double-chain metal halide hybrid

Low-dimensional metal halide hybrids with efficient warm white-light emission from self-trapped excitons (STEs) have attracted extensive attention for interior lighting because of their fascinating emission features including high colour rendition, excellent colour stability, and low manufacturing cost. Despite great efforts, the mechanism of STEs in one-dimensional (1D) metal halide hybrids is still unclear, which makes the way to regulate white-light emission is still worth exploring. Here, we prepared a double-chain organic-inorganic metal halide hybrid crystal, (C6H18N2)Pb2Br6∙H2O (DEPBH). Strikingly, DEPBH shows a warm white-light emission with an appropriate correlated colour temperature of 3714 K and high colour rendering index up to 89. Especially, further research reveals that STEs springs from the 1D core-shell quantum-wire frame play a crucial role in such warm white-light emission of DEPBH. This work offers a new route to fabricate single-component warm white-light phosphors in low-dimensional materials and will contribute to the further exploration of their relationships between crystal structure and optical properties.

Color Polymorphism and Room Temperature Phosphorescence of 4-Bromo-2,7-Di-Tert-Butyl- 9-Methoxypyrene.

Color polymorphism combined with crystal packing-dependent luminescence properties of polymorphs reflects differences in intermolecular interactions in different molecular arrangements. The title compound has two polymorphic crystal structures having strikingly different absorption and luminescence spectra that result from different packing motifs in the crystal lattice. The polymorph with brick wall-like packing of molecules is white and shows very weak violet fluorescence whereas the second polymorph, where molecules are arranged in columnar stacks, is bright yellow and displays intense green fluorescence with maximum at 487 nm (20530 cm-1). In the white polymorph, where the distance between neighboring chromophores is increased, absorption and fluorescence spectra are similar to those of monomer in solution, and intersystem crossing to triplet manifold is the dominant pathway of relaxation. In the yellow polymorph, molecules within the columnar stacks are rotated which mitigates the steric hindrance and leads to closer π-stacking of the pyrene cores. That increases the ππ overlap and strengthens intermolecular interactions decreasing energy of the excited states. This affects emission spectra and photophysical processes-fluorescence yield grows whereas triplet formation yield decreases when S1 is lowered below higher triplet states and conditions for effective vibronic spin-orbit coupling are not favorable. The effect is not observed for other similar pyrene derivatives, testifying the uniqueness of the phenomenon.

Structural, optical, and radiation shielding properties of cyclosilicates crystals: Hirshfeld topological geometries

Structural, optical, and radiation shielding properties of cyclosilicates crystals: Hirshfeld topological geometries

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.

Study on the rapid growth technology and optical properties of KAP crystal

Compared with the traditional slow evaporation solution technique to grow KAP crystals, we have improved a set of Rapid Growth Technology of Continuous Filtration System based on existing research conditions. KAP crystals were grown by program-controlled solution cooling method. A KAP crystal with a size of 220 mm × 170 mm × 45 mm and a weight of 1934.9 g was successfully grown, which is the largest KAP crystal reported so far. The optical studies such as transmittance, absorption coefficient, optical energy band gap, photoluminescence, and Z-scan of the crystal show that the crystal is more excellent than the traditional slow evaporation solution technique.

Optical properties of La2MgSnO6: Eu3+/Mn4+ double-perovskite phosphors for multifunctional applications

A series of Eu3+/Mn4+ doped La2MgSnO6 double-perovskite phosphors were successfully synthesized by solid-state method. The crystal structure, optical properties, and temperature sensitivity of the phosphors were investigated systematically. Under excitation at 310 and 394 nm, the La2MgSnO6: Eu3+, Mn4+ phosphor exhibits intense red emission of Mn4+ (2Eg→4A2g) and orange-red emission of Eu3+ (5D0→7F2). Within the temperature range of 298–473 K, Eu3+ exhibits excellent thermal stability, whereas the Mn4+ shows significant thermal quenching behavior. A luminescence thermometer for dual-wavelength operation with high sensitivity was designed based on the fluorescence intensity ratio (FIR) method. The value of maximum relative sensitivity (Sr) was calculated as 1.58 % K−1 at 423 K. Particularly, the wavelength-dependent of La2MgSnO6: Eu3+, Mn4+ phosphor was investigated over a range of 270–340 nm, revealing promising potential with a remarkably high maximum wavelength sensitivity of 18.2 % nm−1 at 300 nm. Subsequently, a prototype LED device was fabricated by integrating the La2MgSnO6: Eu3+, Mn4+ phosphors and a near-UV LED chip, demonstrating significant spectral overlap with the absorption curves of plant pigments. These results suggest that the La2MgSnO6: Eu3+, Mn4+ multifunctional phosphor has promising applications in optical thermometry, wavelength detection, and promoting plant growth.

Unravelling the polymorphic characteristics of carbamazepine through additive-assisted sonocrystallisation

ABSTRACT This paper investigates the influence of additives on the antisolvent crystallisation process of carbamazepine (CBZ) using methanol as the solvent and water as the antisolvent, with ultrasonic irradiation at a specific solvent-to-antisolvent (S/A) ratio of 1:2 and a 30-watt power ultrasonic horn. Various additives, such as Hydroxypropyl Methyl Cellulose (HPMC), Bovine Serum Albumin (BSA), Tween 80, and Sodium Dodecyl Sulphate (SDS), were employed to examine their effects on the morphology, stability (including suspension and thermal stability), crystallinity, and polymorphism of CBZ crystals. Raw CBZ exhibited irregular shapes during crystallisation, while SDS addition resulted in both plate-like and needle-like crystals. Conversely, BSA, HPMC, and Tween 80 induced the formation of needle, plate, and block-like crystal structures, respectively. Suspension stability ranked as SDS > BSA > HPMC > Tween 80. Regarding polymorphism, HPMC favoured Form 1, BSA and SDS favoured Form IV, and Tween 80 favoured Form I. Additionally, Tween 80 depicted similar preference for Form I polymorph as HPMC. Notably, Form II and Form III polymorphs were present to varying degrees in all samples, except for Tween 80. This study provides crucial insights into the controlled crystallisation of CBZ and the impact of additives on crystal properties, offering valuable information for tailoring CBZ crystal production for specific pharmaceutical applications.

Study on the electromagnetic properties and microwave absorption properties of Co2Si by non-magnetic metal Cu and Mn single doping

In this study, Co2Si and Co2Si-doped powder materials with different Cu,Mn proportions were prepared by mechanical alloying and thermal sintering. The effects of Cu,Mn doping on the crystal structure, magnetic properties, and microwave absorption properties of Co2Si were investigated. The results showed that all the sample peaks obtained by XRD measurement were consistent with the standard card (ICDD: 98-005-2281) of Co2Si.The Ms values corresponding to 2 wt%, 4 wt%, and 8 wt% Cu doping were 25.79 emu/g, 23.79 emu/g, and 21.75 emu/g, respectively. The saturation magnetization of Co2Si samples doped with 2 at%, 4 at% and 8 at% Mn was 8.26 emu/g, 20.33 emu/g and 14.65 emu/g, respectively.The doping of Cu significantly improved the comprehensive absorption performance of Co2Si alloy, and the lowest reflection loss was obtained when Cu was doped with Co2Si alloy, with an RLmin value of -67.61 dB and an EAB of 2.40 GHz. The comprehensive absorption performance of Mn doped Co2Si was also improved, and the RLmin value of Mn doped with 4 at% was -67.04 dB, and the EAB was 2.39 GHz.This is because that the small Co2-xMxSi (M=Cu,Mn) alloy can produce multiple reflection and scattering effects, which increase the propagation path of the electromagnetic wave and optimize the impedance matching characteristics of the material.

Inverse design of topological photonic time crystals via deep learning

Photonic time crystals are a new kind of photonic system in modern optical physics, leading to devices with new properties in time. However, so far, it is still a challenge to design photonic time crystals with specific topological states due to the complex relations between time crystal structures and topological properties. Here, we propose a deep-learning-based approach to address this challenge. In a photonic time crystal with time inversion symmetry, each band separated by momentum gaps can have a non-zero quantized Berry phase. We show that the neural network can learn the relationship between time crystal structures and Berry phases, and then determine the crystal structures of photonic time crystals based on given Berry phase properties. Our work shows a new way of applying machine learning to the inverse design of time-varying optical systems and has potential extensions to other fields, such as time-varying phononic devices.

Insights into the potential mechanism of diversified freezing techniques' influence on quality of golden pompano (Trachinotus ovatus): Focus on freezing speed, ice crystal morphology, water migration, and texture properties

The influences of air freezing (AF), liquid nitrogen freezing (LNF), immersion freezing (IF), magnetic field-assisted immersion freezing (MIF), and ultrasound-assisted immersion freezing (UIF) on the freezing time, water holding capacity, texture profile analysis (TPA), and microstructure of the golden pompano (Trachinotus ovatus) muscle was investigated. The findings indicated that the MIF and UIF groups were more effective in reducing the freezing time than other freezing method, with 84.35% and 85.81% shorter than that of AF, respectively. Among all the treatments, MIF had the best muscle integrity and closely packed myogenic fibers, which were more beneficial for maintaining the water holding capacity, textural properties, and color of the golden pompano muscle. Among all the groups, the MIF quality was the closest to unfrozen samples. Therefore, MIF effectively reduced the size of ice crystals, and inhibited the quality deterioration of frozen golden pompano.

The comparative study of PP-b-PE block copolymer and ethylene-octene block copolymer on crystallization, structure and mechanical property of high-density polyethylene/polypropylene blends

Olefin block copolymers can improve the compatibility between polyethylene (PE) and polypropylene (PP). The work studied the impact of ethylene-propylene multiblock copolymer (PP-b-PE) and ethylene-octene block copolymer (OBC) on the crystallization behavior, mechanical properties, phase structure, and interfacial interactions of HDPE/PP blends. The result showed that PP-b-PE promotes the crystallization temperature and rate of both HDPE and PP, while OBC primarily affects the crystallization behavior of HDPE. The addition of PP-b-PE, as evidenced by small angle X-ray scattering (SAXS), further weakened the interface region between HDPE and PP compared to OBC, indicating enhanced compatibility between HDPE and PP, further confirmed by the stronger adhesion of PP-b-PE to PP and HDPE compared to OBC in peel test. Surface morphology and surface energy analysis demonstrated that PP-b-PE can form a core-shell structure with PP by encapsulating PP, similar to OBC-PP core-shell structure, reducing the interfacial tension between HDPE and PP that effectively transfers stress to the PP phase. The improved compatibility of HDPE/PP resulted in higher elongation at break and equivalent impact strength to HDPE.

High second-order nonlinearity in single-domain tetragonal PMN-PT single crystal

Recently, Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals present tremendous potential in optical applications such as Q-switches and invisible robotic devices because they possess high electro-optic properties and perfect transparency simultaneously. However, due to the difficulties in testing and sample preparation, the nonlinear optical properties of PMN-PT single crystals have not been reported yet, which poses a bottleneck for exploring its nonlinear application. In this work, a large second-order nonlinear coefficient (d31 ∼ 77.9 pm V−1) of single domain PMN-0.39PT single crystal has been revealed, which is times times higher than the maximum nonlinear coefficient of commercial LiNbO3 single crystal (d33 = 25.4 pm V−1). The complete set of nonlinear coefficients of the sample has been determined by second harmonic generation microscopy. This work presents the promising nonlinear optical property in PMN-PT single crystals and opens a door for designing high-performance nonlinear optical devices.

Rewc-GNN Algorithm for the Property Prediction of Large-Scale Crystals.

The space group of a crystal describes the symmetry and periodic arrangement of its structure. As the fundamental element in the structure, it plays a vital role in determining the physical and chemical properties of crystals. The investigation of crystal space group information allows for the prediction of material properties, thereby providing guidance for material design and synthesis to enhance their performance or functionality. Currently prevalent first-principles-based computational methods exhibit good accuracy, but they rely heavily on computing resources, greatly limiting the efficiency of material screening. In this paper, our study is oriented toward the prediction the spatial group of crystals, and an algorithm named Rewc, based on graph neural networks (GNNs) is proposed. This algorithm encodes all atoms and the interactions between atoms in the crystal as features by combining Floyd algorithm and k-hop message passing and employs multilayer convolutional networks to extract connections between k layers. This allows for the automatic learning of more representative atomic vector representations through iterations of feature information for each atom and its neighbors. Experimental results demonstrate that the Rewc framework exhibits reliable accuracy and good generalization capabilities in predicting the crystal structure compared to previous GNN methods.

A Visual Representation for Accurate Local Basis Set Construction and Optimization: A Case Study of SrTiO3 with Hybrid DFT Functionals

The linear combination of atomic orbitals (LCAO) method is advantageous for calculating important bulk and surface properties of crystals and defects in/on them. Compared to plane wave calculations and contrary to common assumptions, hybrid density functional theory (DFT) functionals are actually less costly and easier to implement in LCAO codes. However, choosing the proper basis set (BS) for the LCAO calculations representing Guassian-type functions is crucial, as the results depend heavily on its quality. In this study, we introduce a new basis set (BS) visual representation, which helps us (1) analyze the collective behavior of individual atoms’ shell exponents (s, p, and d), (2) better compare different BSs, (3) identify atom-type invariant relationships, and (4) suggest a robust method for building a local all-electron BS (denoted as BS1) from scratch for each atom type. To compare our BS1 with the others existing in the literature, we calculate the basic bulk properties of SrTiO3 (STO) in cubic and tetragonal phases using several hybrid DFT functionals (B3LYP, PBE0, and HSE06). After adjusting the exact Hartree–Fock (HF) exchange of PBEx, HSEx, and the state-of-the-art meta-GGA hybrid r2SCANx functionals, we find the r2SCAN15 and HSE27 for BS1, with the amount of exact HF exchange of 0.15 and 0.27, respectively, perform equally well for reproducing several most relevant STO properties. The proposed robust BS construction scheme has the advantage that all parameters of the obtained BS can be reoptimized for each new material, thus increasing the quality of DFT calculation predictions.

The effect of stress gradient on the formation of topologically close packed phases in a Ni-based single crystal superalloy at 1050 °C

The formation of topologically close packed (TCP) phases is detrimental to the mechanical properties of Ni-based single crystal (SX) superalloys, which are used in harsh environments with high temperature and gradient stress caused by centrifugal force during service. In order to study the precipitation behavior of TCP phases in coupling with temperature and stress gradient, a third generation Ni-based SX superalloy is selected to conduct force holding experiments at 1050 °C for 8 hours. Stress gradient can be realized under constant load by designing tensile samples with cross-sectional area continuously changed. The results indicate that the area fraction of TCP phases varies at different positions of the sample, where the effective tensile stress is different. The area fraction of TCP phases decreases at the thinner region of the sample, which means that the amount of TCP phases decreases as applied stress increases. At the thinnest position, where the stress is estimated to be 400 MPa, almost no TCP was observed. The inhibition of stress on the formation of TCP phase may be due to the reduction of Re concentration in the γ matrix, because of the segregation of Re at γ/γ′ phase interfacial dislocation cores and the dissolving of γ′ phase.

First-principles calculation of structural, electronic, optical, and mechanical properties of SrVO3.

CONTEXT AND RESULTS: In this paper, the crystal structure, electronic, optical, and mechanical properties of SrVO3 have been systematically studied by first-principles calculation. The results show that the calculated lattice parameters are in good agreement with the experimental values of X-ray diffraction. The density of states is described in detail in this paper. By analyzing the crystal structure and electronic properties of SrVO3, the magnetic properties of SrVO3 are obtained from the one unpaired electrons of V and the exchange interaction between two V ions. At the same time, a detailed analysis of the optical properties of SrVO3 was conducted, and it was found that it is transparent in the visible light range. Finally, the mechanical properties of SrVO3 are calculated, which can provide some references for future research. COMPUTATIONAL METHOD: In this paper, a first-principles method based on density functional theory (DFT) is reported for PBE-GGA analysis using the plane wave-pseudo potential method in a quantum concentrate packet, U value of 7 eV to V-d and a U value of 2 eV to O-p, Grimme correction by DFT-D method. The k points in the Brillouin region are set to 4 × 4 × 4. The energy convergence criterion for self-consistent field calculation is set at 5.0 × 10-6 eV/atom, and the cutoff energy is 1170eV. In this paper, the force acting on each atom is not more than 0.01 eV/Å, the maximum stress is not more than 0.02GPa, and the maximum atomic displacement is 5 × 10-4Å.

Topology classification in bi-anisotropic topological photonic crystals via the Wilson loop approach [Invited

Topological photonic crystals have attracted tremendous attention due to their promise of robust optical properties and great potential for applications in on-chip devices. Numerous successful experimental demonstrations have shown or proved their topological properties, however, many of them turn out to have a nature of fragile topological phases. Here, using theoretical methods of fragile topology, we analyze two cases of topological photonic crystals with preserved time reversal symmetry, which utilize (1), the intrinsic duality and bi-anisotropy, and (2), accidental duality and structural bi-anisotropy respectively to induce their topological order. Our results show that the former case belongs to a Wannier-obstructed type of topological phase, indicating strong topological protection in their edge states. However, the latter meta-waveguide designs with structural bi-anisotropy widely implemented in experiments are Wannierizable, implying the fragile properties of their topology and gapped edge spectra. Our results provide new insights into the topological properties of photonic crystals as well as other bosonic systems with time-reversal symmetry.

Manganese dioxide nanoparticles and nanocomposites with carbon black. Synthesis, physical-chemical and electrical properties

In this study, α- and β-MnO2 and composites with carbon black (CB) were chemically synthesized and prepared through mechanical mixing respectively. The samples’ crystal structure, morphology, and electrical properties have been investigated herein. It is found that average particle sizes of 12–15 nm and 18–24 nm for α- and β-MnO2, respectively. The surface area and average pore volume of obtained samples of α- and β-MnO2 are 200 and 70 m2/g, and 3.2 and 5.3 nm, respectively. The electrical conductivity performances and activation energy behavior of samples have been analyzed. The correlation between the CB content in the composites and their electrical conductivity was established based on experimental data. The electrical conductivity of the α-MnO2/C monotonic increase from 1.31 to 18.6 S/m. There was a 7.5-fold increase of conductivity for α-MnO2 with 15 wt.% CB and almost a 30-fold increase for β-MnO2 with the corresponding CB content compared to the pure samples. In composite samples, the activation energy decreases from 0.069 to 0.041 eV and from 0.154 to 0.074 eV for α- and β- MnO2/C, respectively.

Pressure-induced metallization in Pb3Mn7O15

The multiferroic material Pb3Mn7O15 exhibits a high resistivity arising from the orbital electrons localized around the manganese ions, which hinders its potential applications. Previous studies indicated that the resistivity of Pb3Mn7O15 was influenced by its crystal structure and the distribution of Mn ions. Consequently, pressure-induced structural change are expected to represent a viable method for tuning the resistivity and other properties of this compound. In the present study, the pressure effect on the resistivity of Pb3Mn7O15 was investigated up to 42 GPa. Furthermore, the X-ray diffraction and Raman spectroscopy techniques, along with the density functional theory calculations were employed to study the crystal structure evolution of Pb3Mn7O15 under pressure. The results demonstrate an electronic semiconductor-metal phase transition in Pb3Mn7O15, accompanying an irreversible orthorhombic to monoclinic phase transition. Additionally, within the orthorhombic phase, an iso-structural phase transition is observed, originating from the magnetic moments collapse of manganese cations. This study provides compelling evidence that high-pressure processing can be employed to modulate the crystal structure and functional properties of multifunctional materials.

Achieving a Rapid Na+ Migration and Highly Reversible Phase Transition of NASICON for Sodium-Ion Batteries with Suppressed Voltage Hysteresis and Ultralong Lifespan.

Sodium ion batteries have attracted great attention for large scale energy storage devices to replace lithium-ion batteries. As a promising polyanionic cathode material of sodium-ion batteries, Na3V2(PO4)2F3 (NVPF) belonging to NASICON exhibits large gap space and excellent structural stability, leading to a high energy density and ultralong cycle lifespan. To improve its stability and Na ion mobility, K+ cations are introduced into NVPF crystal as in situ partial substitution for Na+. The influence of K+ in situ substitution on crystal structure, electronic properties, kinetic properties, and electrochemical performance of NVPF are investigated. Through ex situ examination, it turns out that K+ occupied Na1 ion, in which the K+ does not participate in the charge-discharge process and plays a pillar role in improving the mobility of Na+. Moreover, the doping of K+ cation can reduce the bandgap energy and improve the electronic conductivity. Besides, the optimal K+ doping concentration in N0.92K0.08VPF/C is found so as to achieve rapid Na+ migration and reversible phase transition. The specific capacity of N0.92K0.08VPF/C is as high as 128.8 mAh g-1 at 0.2 C, and at 10 C its rate performance is excellent, which shows a capacity of 113.3 mAh g-1.