Acta crystallographica Section B, Structural science, crystal engineering and materials最新文献

The NaZr₂P₃O₁₂ family of materials have shown low and tailorable thermal expansion properties. In this study, SrZr₄P₆O₂₄ (SrO·4ZrO₂·3P₂O₅), CaZr₄P₆O₂₄ (CaO·4ZrO₂·3P₂O₅), MgZr₄P₆O₂₄ (MgO·4ZrO₂·3P₂O₅), NaTi₂P₃O₁₂ [½(Na₂O·4TiO₂·3P₂O₅)], NaZr₂P₃O₁₂ [½(Na₂O·4ZrO₂·3P₂O₅)], and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500°C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr₄P₆O₂₄ and CaZr₄P₆O₂₄ was between -1 × 10^-6 per °C and 6 × 10^-6 per °C from 25 to 1500°C. The crystal structures of the high-temperature polymorphs of CaZr₄P₆O₂₄ and SrZr₄P₆O₂₄ with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above ∼1250°C. This work measured thermal expansion coefficients to 1500°C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.

Phase transitions in Rochelle salt [sodium potassium L(+)-tartrate tetrahydrate] are revisited in a single-crystal X-ray diffraction multi-temperature study on cooling from 308 to 100 K across the high-temperature paraelectric (PE) ↔ ferroelectric ↔ low-temperature PE phase transition points. The results of structure refinement using three different models (a harmonic with and without disorder, and an anharmonic) were compared. The temperature dependencies of anisotropic displacement parameters (ADPs) and U_eq, which can be calculated directly from ADPs, for the low-temperature PE phase indicate clearly the dynamic nature of disorder of the K1 atoms. The structures of the low-temperature and the high-temperature PE phases are compared for the first time at multiple temperatures for each phase based on diffraction data collected from the same single crystal. The data indicate that the high-temperature and the low-temperature paraelectric phases are probably not two different phases, as was assumed in earlier works, but are structurally the same phase at different temperatures.

As an excellent representative of all-inorganic perovskite materials, CsPbBr₃ has been widely used in high-energy rays or high-energy particles detection for its outstanding high carrier mobility and long diffusion length. The great challenges and opportunities in these fields are crystal growth technology, especially the high-quality and large-sized CsPbBr₃ single crystals. In this work, the influences of growth parameters (temperature gradient, growth rate, cooling rate) and thermal stress by the vertical Bridgman method on the quality and performance of CsPbBr₃ crystals are systematically studied. The final results show that 10°C cm^-1 is the optimized temperature gradient and 0.5 mm h^-1 is the suitable growth rate for CsPbBr₃ crystal growth. The study also shows that a cooling rate of 10°C h^-1 for the general temperature interval and 1°C h^-1 for the phase transition temperature interval is helpful to balance crystal growth efficiency as well as crystal quality. Crystal cracks caused by thermal stress as well as crystal adhesion on the ampoule can be effectively solved by depositing a uniform carbon film on the ampoule in advance. The optical, electrical and detection performance are also investigated. The optical characterization in the wavelength region ranging from ultraviolet to infrared indicates the crystal has a low density of deep-level defects and good crystal quality. The resistivity over 10⁹ Ω cm and μτ of electrons over 10^-2 cm^-2 V^-1 proves that the electrical performance of the crystal has met the basic requirement for nuclear radiation detection. The metal-semiconductor-metal structure Ti/Ni/CsPbBr₃/Ni/Ti detector fabricated from the optimized CsPbBr₃ single crystal has an energy resolution of 12.85% (¹³⁷Cs, 662 keV). The purpose of this work is to provide a useful guide and reference for the future exploration of repeatable and improvable CsPbBr₃ crystal growth technology.

Traditional X-ray methods are extensively applied to commercial cement samples in order to determine their physical and chemical properties. Powder patterns are routinely used to quantify the composition of these phase mixtures, but structure determination becomes difficult because of reflection overlapping caused by the high number of different crystal structures. The fast-growing 3D electron diffraction technique and its related automated acquisition protocols arise as a potentially very interesting tool for the cement industry, since they enable the fast and systematic acquisition of diffraction data from individual particles. In this context, electron diffraction has been used in the investigation of the different crystalline phases present in various commercial clinkers for cement. Automated data collection procedures and subsequent data processing have enabled the structural characterization of the different crystal structures from which the α'_H polymorph of Ca₂SiO₄ (belite) exhibited satellite reflections. Its average crystal structure has been known since 1971 and satellite reflections have been reported previously, yet the modulation was never fully described by means of the superspace formalism. Here, the incommensurately modulated structure is solved and refined using harmonic and crenel functions in the superspace group Pnma(α00)0ss, showing the potential of 3D electron diffraction for systematic crystallographic characterizations of cement. A full description of the different belite polymorphs is provided considering this modulated structure.

A significant part of the present and future of optoelectronic devices lies on thin multilayer heterostructures. Their optical properties depend strongly on strain, being essential to the knowledge of the stress level to optimize the growth process. Here the structural and microstructural characteristics of sub-micron a-ZnO epilayers (12 to 770 nm) grown on r-sapphire by metal-organic chemical vapour deposition are studied. Morphological and structural studies have been made using scanning electron microscopy and high-resolution X-ray diffraction. Plastic unit-cell distortion and corresponding strain have been determined as a function of film thickness. A critical thickness has been observed as separating the non-elastic/elastic states with an experimental value of 150-200 nm. This behaviour has been confirmed from ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy measurements. An equation that gives the balance of strains is proposed as an interesting method to experimentally determine this critical thickness. It is concluded that in the thinnest films an elongation of the Zn-O bond takes place and that the plastic strained ZnO films relax through nucleation of misfit dislocations, which is a consequence of three-dimensional surface morphology.

A series of Cu^II complexes obtained under the same reaction conditions has been analyzed to gain insight into the effect of the ligand composition on the final reaction product. Dipodal ligands containing N-donor imidazole rings and a benzene ring as a spacer with different numbers of methyl substituents on the aromatic rings were selected for the study such as 1,3-bis(imidazol-1-ylmethyl)benzene (L1), 1,3-bis(imidazol-1-ylmethyl)-5-methylbenzene (L2), 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L3), 1,3-bis(2-methylimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L4). L4 has not been reported previously and was synthesized for this study. The formed metal complexes show the presence of polymeric (ligand with no or one methyl substituent; 1-4), or discrete motifs (3- or 5-methyl substituents; 5-7). The new metal complexes 3, 5 and 6 were analyzed using single-crystal X-ray diffraction and powder diffraction. In addition, the structural analyses were supported by computational methods.

The crystal structure of zharchikhite, AlF(OH)₂, from the Zharchikhinskoe deposit (Buryatia, Russia) is solved here using single-crystal X-ray diffraction. The mineral is monoclinic, space group P2₁/c, a = 5.1788 (4), b = 7.8386 (4), c = 5.1624 (4) Å, β = 116.276 (10)°, V = 187.91 (3) ų and Z = 4. Zharchikhite demonstrates a novel structure type roughly related to the α-PbO₂ structure type and different from other compounds of the Al-F-OH system. The crystal structure of zharchikhite is based on the octahedral pseudoframework built from zigzag chains of edge-sharing AlF₂(OH)₄ octahedra; adjacent chains are linked via F vertices and the pseudoframework contains wide channels.

The structural strain induced by temperature (`phonon pressure') and radiation damage (`defect pressure') is not necessarily correlated because of different underlying structural mechanisms. Here synchrotron experiments may provide new and yet unexplored opportunities. A recent publication by McMonagle et al. [(2024), Acta Cryst. B80, 13-18] is an excellent illustration of this.

Diacetylenedisalicylic acid is a new rigid linker molecule, capable of forming strong chelate bonds with metal cations. Its monosubstituted salts with dimethylamine and sodium form 1D and 2D coordination polymers, whose structures were solved from single crystals, along with the dimethyl ester of diacetylenedisalicylic acid. The structure of the dimethyl ester is characterized by a dense co-facial π-stacking of molecules with a dominance of van der Waals interactions between the stacks. The angle between the stack direction and the butadiyne groups does not meet the Enkelmann criterion for polymerization in a crystal. In contrast to the dimethyl ester, both salts have a rigid framework with channels filled with disordered solvent molecules. Photoluminescence spectra of the acid and its dimethyl ester have been studied. Thermal analysis of the acid confirms its high thermal stability to 286°C. The acid and its dimethyl ester are prone to polymerization on further heating followed by 50-52% mass loss, forming an amorphous carbon residue at 1000°C.

The interaction of intense synchrotron radiation with molecular crystals frequently modifies the crystal structure by breaking bonds, producing fragments and, hence, inducing disorder. Here, a second-rank tensor of radiation-induced lattice strain is proposed to characterize the structural susceptibility to radiation. Quantitative estimates are derived using a linear response approximation from experimental data collected on three materials Hg(NO₃)₂(PPh₃)₂, Hg(CN)₂(PPh₃)₂ and BiPh₃ [PPh₃ = triphenylphosphine, P(C₆H₅)₃; Ph = phenyl, C₆H₅], and are compared with the corresponding thermal expansivities. The associated eigenvalues and eigenvectors show that the two tensors are not the same and therefore probe truly different structural responses. The tensor of radiative expansion serves as a measure of the susceptibility of crystal structures to radiation damage.