Crystal Growth & Design最新文献

The crystal structure of Ritonavir Form IV is reported. The structure was determined by electron diffraction, and the molecular conformation and hydrogen bonding show similarities to those of Forms I and III. Form II is shown to be the most thermodynamically stable of the four known polymorphs.

The growing demand for nonreciprocal optical devices has intensified the need for high-performance magneto-optical materials. Yttrium iron garnet (YIG) stands out for its excellent magnetic and magneto-optical characteristics. In this work, centimeter-sized dysprosium-doped YIG single crystals were successfully synthesized via the top-seeded solution growth method. The integration of Dy³⁺ ions significantly reduces both coercivity and saturation magnetization compared with pure YIG, enabling magnetic saturation under lower external fields. The as-grown crystal exhibits ferrimagnetic behavior with a saturation magnetization of 9.96 emu/g and a coercivity of 8.40 Oe. Postgrowth oxygen annealing effectively suppresses Fe²⁺ and oxygen vacancy defects, further improving the magneto-optical performance. After annealing at 900 °C, the defect concentration is minimized, leading to a reduced coercivity of 5.09 Oe. Moreover, the treated crystal shows enhanced optical transmittance (71.93% at 1550 nm, 76.05% at 2000 nm), and the Faraday rotation angle increased by more than 12% (184°/cm at 1550 nm, 123°/cm at 2000 nm). These results highlight the essential role of oxygen annealing in optimizing crystal quality and magneto-optical functionality, thus providing critical insights for the property design and postprocessing of magneto-optical materials.

Semi-insulating GaN single crystals were successfully grown on patterned GaN/sapphire substrates using hydride vapor phase epitaxy (HVPE), and the dislocation reduction mechanism was investigated. In the initial stage, selective epitaxy was achieved using photolithographically patterned SiO₂/Ti masks, leading to the formation of truncated GaN micropyramids enclosed by (101̅1) planes. Detailed characterization by cathodoluminescence (CL) and Raman spectroscopy revealed that these structures significantly reduced defect density through a dislocation bending mechanism. Subsequently, lateral overgrowth coalescence produced hexagonal pits composed of (112̅2) planes, which further concentrated dislocations toward the center and reduced their density. An in-source codoping strategy with Ga and Fe/Mn metals enabled the successful fabrication of semi-insulating GaN single crystals. X-ray diffraction and optical spectroscopy demonstrated that the obtained crystals exhibited low dislocation density and minimal residual stress, while resistivity measurements confirmed their excellent semi-insulating properties. This approach provides a new pathway for preparing high-quality free-standing semi-insulating GaN substrates and holds significant potential for the development of high-power radio frequency devices.

A new high-pressure polymorph of barium tellurate, HP-BaTeO₃, was synthesized using multianvil high-pressure/high-temperature techniques (4 GPa, 900 °C). The compound crystallizes in the monoclinic space group P2₁/c and consists of stacked trigonal pyramidal [TeO₃]^2– units interconnected by secondary bonds. Structural analysis identifies significant differences between HP-BaTeO₃ and its ambient-pressure polymorph, BaTeO₃(I), including a doubling of the c-axis and additional secondary bonding within the bc plane. The optical properties of HP-BaTeO₃ were investigated using ultraviolet–visible spectroscopy, revealing a widened bandgap compared to BaTeO₃(I), attributed to changes in orbital overlap and lone pair orientation. Thermal analysis and high-temperature powder X-ray diffraction confirmed the metastable nature of HP-BaTeO₃, with a phase transition to BaTeO₃(I) occurring at approximately 550 °C. This study highlights the structural and electronic modifications induced by high-pressure synthesis and provides insights into the relationship between the two polymorphs.

Using density functional calculations, we systematically examine the adsorption characteristics of Ga and N atoms on stepped and kinked vicinal GaN(0001̅) surfaces under metal–organic vapor-phase epitaxy (MOVPE) growth conditions. The calculations reveal that surface reconstruction exerts a pronounced influence on the adsorption characteristics of Ga and N adatoms in the vicinity of step edges and kinks. In particular, we find that both Ga and N adatoms can be incorporated at kinks and step edges, in clear contrast to the behavior on conventional Ga-polar GaN(0001) surface. These findings provide valuable insights into the atomistic mechanisms governing the epitaxial growth of N-polar GaN, thereby advancing our understanding of the surface processes that determine crystal quality and morphology during the MOVPE growth.

We report the synthesis, crystal structure, and physical properties of a new layered telluride, Nb_1.1Fe_1.8Te₄, with an orthorhombic Pmmn (No. 59) structure that features mixed Nb/Fe occupancy on an octahedral site and positional disorder of Fe on a partially filled tetrahedral interstitial site. Magnetic measurements uncover a canonical spin-glass transition at ∼25 K, supported by frequency-dependent ac susceptibility. Transport studies show semiconducting-like resistivity arising from a combination of a metallic channel and two-dimensional variable-range hopping, together with negative magnetoresistance attributable to spin-disorder scattering. Nb_1.1Fe_1.8Te₄ displays remarkably similar magnetic and transport properties as a material with different occupancies and symmetry, highlighting the disordered Fe–Te framework in stabilizing glassy magnetism.

Nanoparticles are widely adopted to control crystallization due to their remarkable ability to modify crystal properties at the molecular level. Nanoparticles with suitable surface characteristics can selectively enhance or suppress nucleation and crystal growth. Silica nanoparticles, in particular, are extensively used as texture modifiers in the food industry and flow improvers in the petroleum industry. However, the precise details of their modus operandi remain poorly understood. We report the effect of silica nanoparticles, hydrophobized with octadecyl chains, on the kinetics of wax crystallization and the flow properties of a model waxy oil. Quantification of the density of hydrocarbon chains on nanoparticles showed that the grafting consists of multiple layers. The addition of these nanoparticles inhibited wax nucleation, estimated as a nanoparticle concentration-dependent effective activation energy of nucleation. There was also a change in the morphology of wax crystals from plate-like crystals to large, branched structures, resulting in a reduction of viscoelastic moduli and yield stresses by more than one order of magnitude. SEM images further revealed that nanoparticles are adsorbed along plate edges, reducing growth in that direction and thereby causing branching. These insights can be extended to other systems where nanoparticles can be used to tune the nucleation and growth mechanisms during crystallization.

The rational design of photocatalytically active metal–organic frameworks is essential for advancing sustainable and selective synthesis. Herein, we report a zirconium-based MOF (Zr-TB-fcu-MOF) assembled from a π-extended, nitrogen-rich benzo(triazole-thiadiazole) linker. The incorporation of a donor–acceptor–donor (D–A–D) architecture within the fcu-type framework induces pronounced intraframework electronic polarization, facilitating efficient photoinduced charge separation under visible-light irradiation. Structural and spectroscopic analyses reveal that the crystalline network exhibits high porosity, suitable band alignment, and good chemical stability. These combined characteristics enable Zr-TB-fcu-MOF to function as a robust and recyclable heterogeneous photocatalyst, promoting the atom-economical synthesis of nitrogen-containing compounds under mild additive-free conditions. The catalyst mediates the formation of symmetrical (up to 85% yield) and unsymmetrical (up to 40% yield) thiadiazoles as well as imines (up to 99% yield), showing good tolerance toward the functional groups present in the tested substrates and maintaining catalytic activity over multiple cycles. This work demonstrates a structure-guided approach for engineering MOF-based photocatalysts with tunable electronic structures for visible-light-driven organic transformations.

Zero-dimensional (0D) Mn²⁺-based organic–inorganic metal halides (OIMHs) have garnered significant attention in the field of white light-emitting diodes (WLEDs) due to their low toxicity, high photoluminescence quantum yield (PLQY), small full width at half-maximum (fwhm), and good stability. In this study, we report the synthesis and luminescence characterization of six novel 0D Mn²⁺-based OIMHs with the general formula [R–Ph₃P]₂MnX₄ (where R = −CH₃, −C₂H₅, −C₃H₅, −Ph, and −CH₂Ph; X = Cl/Br), which were fabricated via an environmentally friendly minimal-solvent ionothermal method. All compounds exhibit bright green emission (506–523 nm) under blue light excitation, narrow fwhm (43–48 nm), high color purity (87–94%), and high thermal stability (>280 °C). Notably, [PhCH₂–Ph₃P]₂MnBr₂Cl₂ achieves a near-unity PLQY of 92.76% under 450 nm excitation, while [C₃H₅–Ph₃P]₂MnBr₂Cl₂ demonstrates an excellent photoluminescence lifetime of 632.89 μs. A WLED was fabricated by combining [PhCH₂–Ph₃P]₂MnBr₂Cl₂ with a commercial phosphor and a blue GaN chip (λ_em = 450 nm), yielding a correlated color temperature of 5502 K and CIE 1931 color coordinates of (0.312, 0.317). This work not only establishes a green synthesis pathway for high-performance Mn²⁺-based luminescent materials but also offers valuable insights into their application in advanced lighting technologies.

Sr²⁺ codoped LaBr₃:Ce³⁺ scintillation crystals exhibit exceptional performance in various radiation detection applications, achieving near-theoretical energy resolution (2%) through optimized codoping strategies. However, the substantial doping concentrations required (0.35–0.7 mol %) introduce significant challenges in crystal growth, particularly defect formation, which limits large-scale production and practical application. Herein, this study investigates SrBr₂-induced defect dynamics during crystal growth with a focus on the role of inclusion defects in degrading scintillation performance. The inclusion density increases along the crystal growth direction and follows the matrix-controlled morphological evolution, eventually forming well-defined polyhedral morphologies with equilibrium hexagonal prism bounded by {1000} and {1010} facets. Constitutional supercooling-induced interface instabilities emerge as the primary mechanism driving inclusion formation. Crucially, increasing inclusion density along the growth direction leads to enhanced photon scattering, significantly reducing transmittance, light output, and energy resolution─from 2.69 to 5.9%. In addition, the scattering of scintillation photons by inclusion introduced an additional slow decay component in the scintillation time profile. By leveraging these insights, we optimized growth parameters to suppress this instability, achieving improved crystal quality with an energy resolution of 2.44%@662 keV─a significant improvement compared to conventional methods. These observations quantitatively reveal the influence of macroscopic inclusions, establish a comprehensive framework for macroscopic defect engineering in LaBr₃-based scintillators, and further provide effective strategies for control and optimization of metal halide scintillators.