Crystal Growth & Design最新文献

We report a comparative high-pressure study of two fluorite-type rare-earth oxides with increasing configurational entropy, (CePr)O_2–δ and (CePrLa)O_2–δ. Synchrotron-based powder X-ray diffraction and Raman spectroscopy were carried out up to 30 and 20 GPa, respectively. Both compounds retain the cubic fluorite structure throughout the pressure range explored, although an anomaly is observed between 9 and 16 GPa, characterized by a compressibility plateau and changes in vibrational modes. This behavior is attributed to local lattice distortions and a progressive bond angle bending rather than abrupt phase transitions. In (CePrLa)O_2−δ, the onset of amorphization is observed above 22 GPa, highlighting its reduced structural stability. The bulk modulus of both systems shows a slight decrease after the onset of the anomaly, suggesting subtle lattice softening. Raman spectroscopy reveals suppression of the F₂g mode intensity with increasing cationic disorder, and under compression, partial reordering is evidenced by an increase in the RE–O mode intensity. Our results highlight the complex interplay between configurational entropy, cation size, and pressure in determining the structural stability and vibrational properties of rare-earth high-entropy oxides and provide insight into the mechanisms governing their resilience and local disorder under extreme conditions.

Increasing configurational entropy modulates the high-pressure response of fluorite-type rare-earth oxides. Both (CePr)O_2−δ and (CePrLa)O_2−δ exhibit a compressibility anomaly driven by bond-angle distortion, while La-containing compositions undergo reversible amorphization. Raman data reveal pressure-induced local reordering, establishing entropy as a key variable in oxide robustness under extreme conditions.

Experimental and theoretical studies on two 2-hydroxynaphthalene imine-based compounds, namely, 1-[{(2,4-dichlorophenyl)imino}methyl]naphthalen-2-ol (24Clmno) and (E)-N-(2,4-dichlorophenyl)-2-{(2-hydroxynaphthalen-1-yl)methylene}hydrazine-1-carbothioamide (24Clhhc), to establish the energetically favorable enol-imine form in their respective crystal structures are reported. The structure of 24Clmno has edge-on chlorine−π interactions and also C–H···O interactions among neighboring molecules to form chain-like arrangements. The self-assembly of 24Clhhc was devoid of chlorine−π interactions but guided by C–H···S interactions, forming double-chain-like arrangements forming a layer-like structure. Theoretically, the enol-imine form of 24Clmno is more stable by 38.52 kJ/mol than the keto-amine form, whereas in the case of 24Clhhc, the enol-imine form is more stable than the keto-amine, which was stable by 129.5 kJ/mol. Energy calculation by density functional theory on a series of compounds adopted from the literature showed that an energetically favorable tautomeric form is generally observed; the stabilities are also guided by the substituents and their positions in such molecules. The solvatochromic and solvatoemissive properties of these compounds were studied, and results were analyzed with the aid of nuclear magnetic resonance, emission lifetime measurements, and different control experiments in solution. Interactions of 24Clhhc with alkali and alkaline-earth metal ions, and under basic conditions, caused enhancement of fluorescence intensity at 509 nm. The zinc and cadmium ions do not cause fluorescence emission of the 24Clmno, but the emission of 24Clhhc changes by these two ions in a distinguishable manner. Zinc ions shifted the emission peak toward higher wavelengths, and cadmium ions to lower wavelengths.

Atomically thin, perforated graphene on c-plane sapphire functions as a nanoscale mask that enables GaN growth through thru-holes. We tune the perforated-area fraction f_p by controlled O₂-plasma exposure and quantify its impact on early stage nucleation: the nucleation-site density scales with f_p, while the nucleation-delay time decreases approximately as 1/f_p. Time-resolved areal coverage and domain counts exhibit systematic f_p-dependent trends. A kinetic Monte Carlo (kMC) model that coarse-grains atomistic events─adatom arrival, surface diffusion, attachment at exposed sapphire within perforations, and coalescence (the first front–front contact between laterally growing domains)─reproduces these trends using a constant per-site nucleation rate. Fitting the kMC simulation data yields onset times t₀ for the nucleation delay that closely match independently observed no-growth thresholds (Set 1:28.5 s vs ∼ 30 s; Set 2:38 s vs ∼ 35 s), validating the kMC–experiment mapping and highlighting plasma dose as an activation threshold for plasma-induced thru-hole formation in 2D materials. Together, experiment and kMC identify f_p as a single, surface-engineerable parameter governing GaN nucleation statistics on perforated graphene masks, providing a quantitative basis and process window for epitaxial lateral overgrowth/thru-hole epitaxy workflows that employ two-dimensional masks.

l-isoleucine exists in two enantiotropically related polymorphs, α and β, which are both zwitterionic in crystalline and solution states. These forms are conformational polymorphs, distinguished by their hydrogen bonding networks, where the α form exhibits a parallel arrangement, while the β form displays nonparallel interactions, reflecting differences between their respective crystal packings. The crystal morphology, molecular conformation and stability, intermolecular (synthonic) interactions, and surface chemistry of both l-isoleucine polymorphs are examined using synthonic and crystallographic modeling. The β form is found to have stronger intermolecular interactions due to its more efficient arrangement of hydrogen bonds, better packing coefficient, and less void space. This is reflected in the lattice energy for the β form, which is about 15% higher than that for the α form, reflecting its shorter and more linear hydrogen bond network. The NH₃⁺···O hydrogen bonding is found to be the strongest bulk (intrinsic) synthon for both forms, reflecting the higher % contribution to their lattice energies. The predicted morphologies for the two forms are found to be almost identical, i.e., displaying a hexagonal cross-section elongated along the b-axis. The anisotropic growth of the morphology reflects the large variation in the attachment energy values for the important morphological facets of both forms. The anisotropic nature of the growth morphology in both forms is further rationalized through examination of the extrinsic (surface-terminated) synthon contributions to the crystal habit surfaces, where the synthons contributing to respective attachment energies are found to be stronger at the capping surfaces than at the more morphologically dominant surfaces.

Four relevant dimer dysprosium compounds, namely, [Dy₂(OAc)₆(H₂O)₂]·4H₂O (1), [Dy₂(OAc)₆(L¹)₂] (2), [Dy₂ (OAc)₆(L²)₂] (3) and [Dy₂(OAc)₆(L³)₂]·2CHCl₃ (4) and their corresponding Y^III diluted analogues [Dy_0.22Y_1.78 (OAc)₆(H₂O)₂]·4H₂O (1@Y), [Dy_0.23Y_1.77(OAc)₆(L¹)₂] (2@Y), [Dy_0.23Y_1.77(OAc)₆(L²)₂]·2CH₃OH (3@Y), and [Dy_0.22Y_1.78(OAc)₆(L³)₂]·2CHCl₃ (4@Y), have been synthesized (L¹ = 2,2’-bipyridine, L² = 1,10-phenanthroline, and L³ = dipyrazine [2,3-f:2’,3′-h] quinoxaline). These results allow us to investigate the N-terminal group-containing auxiliary-ligand effect on the magnetic properties. Magnetic studies indicate that compounds 1–3 are not single-molecule magnets under zero dc field, but compound 4 is a typical zero-dc-field single-molecule magnet with an effective energy barrier of 112.12(18) K. Compound 1 is not an SMM even under an applied dc field, and compounds 2–3 show SMM behavior under an applied dc field. Moreover, compound 4 exhibits two relaxation processes under an applied dc field. Magnetic studies of the diluted analogues show that the origin of slow magnetic relaxation mainly originates from the single-ion anisotropy of the Dy^III ion. These results further confirm that the ligand field has a significant effect on the magnetic properties of Dy^III compounds.

Ganciclovir (GCV) is a guanine nucleoside analogue with potent activity against cytomegalovirus used in managing severe infections in immunocompromised patients. It is a biopharmaceutical classification system (BCS) class III medication, exhibiting high aqueous solubility but limited membrane permeability, which restricts its absorption in the intestinal membrane. This investigation aimed to identify biologically compatible salts of GCV to enhance its diffusion characteristics through salt formation with aliphatic dicarboxylic acids, namely, oxalic acid (OXA) and maleic acid (MLE). The synthesized organic salts were subjected to solid-state characterization, including powder X-ray diffraction (PXRD), differential scanning calorimetry, and thermogravimetric analysis, as well as Fourier-transform infrared spectroscopy. Rietveld refinement of the PXRD data provided detailed crystal structures, confirming proton transfer from the carboxylic acid groups of the coformers to the N3 atom of the imidazole ring within the guanine moiety of the drug. The GCV–MLE salt was obtained as an anhydrous form, whereas GCV–OXA crystallized as a sesquihydrated salt. Stability studies based on ground-state optimization energies indicated that GCV–OXA possessed superior stability compared with both GCV–MLE and the native drug. Consistently, both salt forms demonstrated notable physicochemical stability for more than one month under controlled conditions of 35 ± 5 °C and 75 ± 5% relative humidities. Evaluation of the solubility and diffusion of the salts, along with the marketed forms of GCV and GCV sodium salt in phosphate buffer (pH 6.8) revealed marked improvements, with aqueous solubility increasing by up to 2-fold and permeation flux enhanced by as much as 5-fold relative to the parent drug. These enhancements are ascribed to the ionic interactions between GCV and the respective salt former. Furthermore, the improved diffusion profiles of the GCV salts showed a positive correlation with their augmented solubility, elevated distribution coefficients, pronounced concentration gradients, and increased polarity conferred by the selected salt coformers.

Phosphate birefringent crystals and nonlinear optical (NLO) crystals are currently in imperative demand for ample applications. However, it is hugely challenging to explore novel phosphate crystals with splendid comprehensive optical and NLO performances due to the drawback of small birefringence. Herein, to address this issue, the strategies of introducing d⁰ transition metal cations with a second-order Jahn–Teller distortion effect into phosphate and fluorination substitution for polarization optimization and optical anisotropy are coherently adopted. As a result, an alkaline-earth phosphate fluoride, Ba₃(MoO₂F₃)PO₄F₂, is designed and synthesized. Benefiting from the synergistic effect of tidily aligned [PO₄]^3– groups and the fluorinated Mo⁶⁺ groups of strongly distorted [MoO₃F₃] polyhedra, the compound exhibits a remarkable birefringence enhancement of 0.062 at 546.1 nm. Theoretical calculation results further indicate that Ba₃(MoO₂F₃)PO₄F₂ is a promising candidate as a novel birefringent crystal. This work promotes the design and discovery of more phosphate birefringent crystals and NLO materials with large birefringence.

Polymorphism remains a major challenge in the development of pharmaceutical solid products as even small changes in the crystal arrangement can influence key properties such as stability and solubility. In this study, we mechanochemically prepared a novel cannabinol piperazine cocrystal, which exists in three polymorphic forms. The formation of these polymorphs was systematically investigated by varying the solvents, temperature, and milling time during the ball mill experiments. Interestingly, the phenomenon of disappearing polymorphs was observed under repeated milling. To get insights into the polymorphic behavior and assess the relative stability of the forms, we analyzed their crystal structures, morphologies, and hydrogen bond motifs and performed particle energy calculations using density functional theory. The theoretical results show good correlation with the experimental data and provide valuable and deep insights into the polymorphic behavior and the disappearance of the metastable form. Overall, this work highlights the importance of integrating structural analysis with energetic evaluations to rationalize and predict polymorph stability and transformations.

Three polymorphs of a new cannabinol piperazine cocrystal were obtained by mechanochemistry, including a metastable polymorph that disappears upon repeated milling. The particle energy calculations offer reasonable insights on the relative stability of the forms.

High-quality growth of Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) epitaxial films is still an interesting research topic for the development of novel high-T_c devices, particularly for scaling THz devices on a single chip. Among various growth techniques, the liquid-phase epitaxy (LPE) technique naturally enables the self-assembly of Bi-2212 epitaxial films at wafer scale. However, the LPE growth mechanism operates within a complexity of solid–liquid thermodynamic equilibrium maintained through stable conditions. Even under well-established protocols, this complex mechanism can be disturbed by process-induced instabilities such as precursor aging, material corrosion, solute accumulation, solvent evaporation, and surface crust formation. As part of a long-term research effort aiming at reliable growth for Bi-2212 films, we have first developed a compact motorized LPE prototype, engineered for precise control and stable maintenance of growth parameters. Under previously optimized conditions implemented into the LPE system, we successfully grew high-quality Bi-2212 epitaxial films. They exhibit a fully aligned film texture, allowing large-area continuous cleavage of the top Bi-2212 layers. This facilitates an in-depth investigation of the crystalline-texture quality across cross-sectional layers, with a focus on crystal disorder, impurity incorporation, and irregular grain nucleation. By systematically eliminating these process instabilities within the LPE mechanism, we evaluated the planar texture consistency and crystalline uniformity of the films and finally outlined the critical requirements of next-generation LPE system, capable of growing Bi-2212 films with large-grain epitaxial texture, which is highly suitable for THz-on-a-chip applications.

Cocrystallization with appropriate organic molecules has been known as an effective and practical strategy for stabilization of organic hydroperoxides─useful oxidants, free-radical polymerization initiators, and emerging pharmaceuticals. In this paper, two peroxosolvates (H₂O₂·HMTA (1), 0.843H₂O₂·0.157H₂O·DABCO N-oxide (2)) and 11 adducts of organic hydroperoxides (2^tBuOOH·DABCO (3), 2CmOOH·DABCO (4), 2^tBuOOH·HMTA (5), 3^tBuOOH·DABCO N-oxide (6), CmOOH·Ph₃PO (7), Cy(OOH)₂·DABCO N-oxide (8), Cy(OOH)₂·DABCO N-oxide·0.5C₆H₆ (9), [Cy(OOH)O]₂·HMTA N-oxide (10), [Cy(OOH)O]₂·DABCO N-oxide (11), [Cy(OOH)O]₂·2DABCO N-oxide·2CHCl₃ (12), [Cy(OOH)O]₂·Ph₃PO (13)) were structurally characterized for the first time, providing the relationships with the nature of components. The energetic superiority of O–H···O^––N⁺ and O–H···O═P over O–H···N hydrogen bonds (E_HB = 30.5–69.3 kJ mol^–1) was against the lower basicity of amine N-oxides and Ph₃PO over amine coformers. This was computationally attributed to the nearly 3-fold increase of partial atomic charges in the former hydrogen bond acceptors, in light of the interaction electrostatic nature. Nine compounds were synthesized according to the proposed facile approach and investigated by FTIR and Raman spectroscopy, thermal analysis, and powder XRD. Thermal stability of the cocrystals was found to be improved by the utilization of heavy coformers and less volatile hydroperoxides, rather than being correlated with hydrogen bond energy.