Crystal Distortion Research Articles

Tailoring the crystal distortion and dielectric properties of 0.7CaTiO3-0.3NdAlO3 microwave ceramics by La, Sm and Eu doping into A-site Nd

The TiO6 octahedra titling and rotation play an important role in affecting the microwave properties of 0.7CaTiO3-0.3NdAlO3 microwave ceramics by A-site La, Sm and Eu doping. The oxygen octahedra of Sm-doped 0.7CaTiO3-0.3NdAlO3 ceramics exhibit antiphase tilting, while both in-phase and antiphase tilting coexist in the 0.7CaTiO3-0.3EuAlO3 ceramics. There is an undeniable correlation between the crystal distortion and the tolerance factor t. As the tolerance factor t continues to increase, the crystal structure of A-site doped CTNA ceramics changes from both in-phase tilting and antiphase tilting to untilted structure and the TiO6 octahedra exhibits an inclination to tilt around c axis. The weakening bending vibration of the Ti–O(2)-Ti bond results in the increase of the polarization and the damping coefficient of lattice vibration. The dielectric constant (εr) rises to 48 from 43 and Q × f values decrease to 36,000 GHz from 44,800 GHz (measured at 6 GHz). These findings could be used to guide the tailoring of the crystal distortion and microwave dielectric properties of technologically important perovskite 0.7CaTiO3-0.3NdAlO3 based ceramics.

Synthesis and mechanistic approach to investigate crystallite size of NbSe2 nanoparticles

Niobium diselenide (NbSe2) belongs to the class of transition metal dichalcogenides (TMDCs) and exhibits peculiar features such as charge density waves, superconductivity, and periodic crystal lattice distortion. The main focus of the article is the synthesis and characterisation of NbSe2 NPs utilising the wet chemical precursor solution route at room temperature, followed by in-depth x-ray diffraction (XRD) characterisation and analysis using the aforementioned techniques. The EDS result demonstrated that the NbSe2 NPs are devoid of impurities and close to stoichiometry. The sample has a crystalline hexagonal structure with the lattice constants a = b = 3.443Å, c = 12.576 Å, and α = β = 90°, γ = 120°, according to the XRD results. The work emphasises the need of comprehending how lattice strain and crystallite size affect physical attributes. x-ray peak broadening was used to study the epitaxial crystallisation of NbSe2 NPs. Various methods for determining crystallite size, such as the Williamson–Hall (W-H) method, Debye–Scherrer plots, uniform deformation model (UDM), uniform stress deformation model (USDM), uniform deformation energy density model (UDEDM), size strain plot (SSP) method, and Halder-Wagner (H-W) method, are employed to comprehensively analyse the nanoparticle characteristics, and additionally, high-resolution transmission electron microscopy (HRTEM) is employed to visualise the morphology and particle size distribution of the synthesised NbSe2 NPs. Physical parameters, including lattice stress, strain, and energy density, are also evaluated more precisely from the XRD pattern reflection peaks. The outcomes shed light on the interplay between crystallite size, lattice strain, and their effects on the material’s properties and showed excellent intercorrelation of the average crystallite sizes as estimated by employing various methods.

Enhanced near-infrared optical transmission in zinc germanium phosphide crystals via precise magnesium doping.

A zinc germanium phosphorus (ZnGeP2) crystal with a chalcopyrite structure is an efficient frequency converter in the mid-infrared region. However, point defect-induced optical absorption at the pumping wavelength (near infrared region) blocked the further application of ZnGeP2. To alleviate the absorption losses caused by point defects, in situ magnesium doping compensation was presented during the ZnGeP2 bulk crystal growth process via the vertical Bridgman method. Combined with theoretical calculations, the structural distortion of the magnesium-doped ZnGeP2 crystals in different orientations was illustrated. The thermodynamic and kinetic stability of the magnesium-doped ZnGeP2 structure were demonstrated. The transmission results indicated the improvement of transmittance within a wavelength range of 1.8-2.4 μm when doped with magnesium, which revealed the powerful ability of the appropriate dopant in optimizing near-infrared optical properties. Thus, the introduction of magnesium is a practical approach to improve the transmittance performance and extend the pumping source wavelengths of ZnGeP2 crystals.

ZnVO3: an ilmenite-type vanadium oxide hosting robust V-V dimers.

Ilmenite-type vanadium oxides exhibit a distinctive cation-dimerization behavior. Here, we report a novel ilmenite-type compound, ZnVO3. Polycrystalline ZnVO3 samples are synthesized under conditions of 10 GPa and 1573 K. The obtained sample crystallizes in the triclinic P1̄ space group. Both V-V and Zn-Zn dimers (dimer-like displacement) are present in the structure, arranged in a ladder-like pattern on each honeycomb lattice. Notably, the V-V dimer persists up to 625 K, surpassing the stability of the V-V dimer state in other ilmenite-type vanadium oxides. Magnetic susceptibility measurements corroborate the formation of direct V-V bond in the dimer. The off-centered position of the Zn2+ ion at the octahedral site, driven by Zn-O covalency and its sp3 nature, promotes the Zn-Zn dimer-like displacement. Cooperative distortions between honeycomb layers further reinforce the V-V dimers. This finding offers insights into controlling cation-dimer strength in crystalline compounds via crystal structure distortions.

Structural engineering of atomic catalysts for electrocatalysis.

As a burgeoning category of heterogeneous catalysts, atomic catalysts have been extensively researched in the field of electrocatalysis. To satisfy different electrocatalytic reactions, single-atom catalysts (SACs), diatomic catalysts (DACs) and triatomic catalysts (TACs) have been successfully designed and synthesized, in which microenvironment structure regulation is the core to achieve high-efficiency catalytic activity and selectivity. In this review, the effect of the geometric and electronic structure of metal active centers on catalytic performance is systematically introduced, including substrates, central metal atoms, and the coordination environment. Then theoretical understanding of atomic catalysts for electrocatalysis is innovatively discussed, including synergistic effects, defect coupled spin state change and crystal field distortion spin state change. In addition, we propose the challenges to optimize atomic catalysts for electrocatalysis applications, including controlled synthesis, increasing the density of active sites, enhancing intrinsic activity, and improving the stability. Moreover, the structure-function relationships of atomic catalysts in the CO2 reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction are highlighted. To facilitate the development of high-performance atomic catalysts, several technical challenges and research orientations are put forward.

Engineering polar distortions in multiferroic Sr1−xBaxMnO3−δ thin films

The physical properties of perovskite oxide thin films are governed by the subtle interplay between chemical composition and crystal symmetry variations, which can be altered by epitaxial growth. In the case of perovskite-type multiferroic thin films, precise control of stoichiometry and epitaxial strain allows for gaining control over the ferroic properties through selective crystal distortions. Here, we demonstrate the chemical tailoring of the polar atomic displacements by tuning the stoichiometry of multiferroic Sr1−xBaxMnO3−δ (0 ≤ x ≤ 0.5) epitaxial thin films. A combination of x-ray diffraction and aberration-corrected scanning transmission electron microscopy enables unraveling the local polarization orientation at the nanoscale as a function of the film’s composition and induced crystalline structure. We demonstrate experimentally that the orientation of polarization is intimately linked to the Ba doping and O stoichiometry of the films and, with the biaxial strain induced by the substrate, it can be tuned either in-plane or out-of-plane with respect to the substrate by the appropriate choice of the post-growth annealing temperature and O2 atmosphere. This chemistry-mediated engineering of the polarization orientation of oxide thin films opens new venues for the design of functional multiferroic architectures and the exploration of novel physics and applications of ferroelectric textures with exotic topological properties.

Nanostructures as the Substrate for Single-Molecule Magnet Deposition.

Anchoringsingle-molecule magnets (SMMs) on the surface of nanostructures is gaining particular interest in the field of molecular magnetism. The accurate organization of SMMs on low-dimensional substrates enables controlled interactions and the possibility of individual molecules' manipulation, paving the route for a broad range of nanotechnological applications. In this comprehensive review article, the most studied types of SMMs are presented, and the quantum-mechanical origin of their magnetic behavior is described. The nanostructured matrices were grouped and characterized to outline to the reader their relevance for subsequent compounding with SMMs. Particular attention was paid to the fact that this process must be carried out in such a way as to preserve the initial functionality and properties of the molecules. Therefore, the work also includes a discussion of issues concerning both the methods of synthesis of the systems in question as well as advanced measurement techniques of the resulting complexes. A great deal of attention was also focused on the issue of surface-molecule interaction, which can affect the magnetic properties of SMMs, causing molecular crystal field distortion or magnetic anisotropy modification, which affects quantum tunneling or magnetic hysteresis, respectively. In our opinion, the analysis of the literature carried out in this way will greatly help the reader to design SMM-nanostructure systems.

Ferrorotational Selectivity in Ilmenites.

Unlike what happens in conventional ferroics, the ferrorotational (FR) domain manipulation and visualization in FR materials are nontrivial as they are invariant under both space-inversion and time-reversal operations. FR domains have recently been observed by using the linear electrogyration (EG) effect and X-ray diffraction (XRD) diffraction mapping. However, ferrorotational selectivity, such as the selective processing of the FR domains and direct visualization of the FR domains, e.g., under an optical microscope, would be the next step to study the FR domains and their possible applications in technology. Unexpectedly, we discovered that the microscopic FR structural distortions in ilmenite crystals can be directly coupled with macroscopic mechanical rotations in such a way that FR domains can be visualized under an optical microscope after innovative rotational polishing, a combined ion milling with a specific rotational polishing, or a twisting-induced fracturing process. Thus, the FR domains could be a unique medium to register the memory of a rotational mechanical process due to a novel selective coupling between its microscopic structural rotations and an external macroscopic rotation. Analogous to the important enantioselectivity in modern chemistry and the pharmaceutical industry, this newly discovered ferrorotational selectivity opens up opportunities for FR manipulation and new FR functionality-based applications.

Thermoelectric Transport of a Novel Zr‐Based Half‐Heusler High‐Entropy Alloy

The high‐entropy concept, extensively studied in alloys and ceramics, has produced intriguing results, but its use in thermoelectric materials is still in its infancy. This study introduces a pioneering high‐entropy half‐Heusler (hH) alloy, ZrTiNiFeSnSb, synthesized via arc melting and heat treatment. Phonon scattering from multiple elements significantly reduces the lattice thermal conductivity of the alloy, which decreases to a minimum of 3.5 Wm−1 K−1 (700 K) in this material. The experimental thermal data matches the density functional theory calculations for phonon dispersion, phonon group velocity, and Grüneisen parameters. This demonstrates that crystal distortion induced anharmonicity slows the alloy's phonon heat transport, which is suitable for thermoelectric applications. Notably possessing elevated electrical conductivity and a moderate Seebeck coefficient, this high‐entropy hH alloy emerges as a promising thermoelectric material for energy harvesting.

A Facilely Synthesized NiCo2S4 with Two Mutually Reinforcing Active Sites for High-Performance Lithium-Sulfur Batteries.

The shuttle effect and slow conversion kinetics of soluble polysulfides hinder the commercial application of lithium-sulfur batteries (LSBs). In this context, we propose a three-dimensional lamellar-stacked nanostructure of nickel cobalt sulfide (D-NiCo2S4) enriched with lattice defects by manipulating the cations in spinel sulfides. It has an obvious synergistic promotion mechanism for the adsorption and catalysis of lithium sulfides. Specifically, Ni3+ on tetrahedral (Td) sites with strong Ni-S covalency anchors LiPSs, whereas Co3+ on octahedral (Oh) sites promotes a highly efficient catalytic conversion of LiPSs, which is confirmed by experimental results and density functional theory (DFT) calculations. Besides, the crystal defects and distortions in the lamellar region could expose more active sites and enhance the redox reaction kinetics of polysulfides. Hence, Li-S batteries with D-NiCo2S4@S as the cathode show outstanding cycle stability; upon cycling at 1 A/g, the battery achieves a high initial specific capacity of 1001.12 and 655.31 mAh g-1 after 1000 cycles (decay rate as low as 0.05% per cycle), as well as a high initial areal capacity of 3.15 mAh cm-2 under high S loading (4.2 mg cm-2). This work provides a viable scheme for designing efficient bimetal sulfide catalysts and furnishes a rational strategy for constructing LSB cathodes with high specific capacity and high area capacity.

Статистичний метод визначення параметрів поля зсувних напружень в площині ковзання в багатокомпонентному сплаві

A method has been developed in which atomic sizes misfit and elastic modulus misfit at crystal lattice nodes are considered as discrete random variables and the definition of their dispersion allows to obtain analytical expressions for standard deviations and correlation lengths of the short- and long-wave components of stochastic shear stress field created by solute atoms in the glide plane in a multicomponent alloy. This makes it possible to significantly reduce the amount of calculations when determining the shear stress field parameters. The developed method was applied to calculate these parameters for the CrCoNiFeMn alloy. The calculated parameters were well correlated with similar parameters determined from the analysis of shear stress distributions in the glide plane, which were calculated by the method of direct summation of solute atoms contributions. In addition, it was found that there are separate effective crystal lattice distortions for the short- and long-wave components that differ from the average distortion that was proposed earlier. This results from the fact that these components are determined by solute atoms with different distance from the glide plane. Effective distortion is greater, the greater this distance from the glide plane. In addition, there is no single empirical constant for all alloy to determine the yield strength as a function of their shear modulus and average distortion. But the proposed method makes it possible to determine the main parameters of the shear stress field in a specific multicomponent alloy. These parameters can be used to calculate the yield strength of this alloy. Keywords: shear stress, multicomponent alloy, glide plane, solid solution.

Encapsulating magnetite nanopowder with fungal biomass: Investigating effects on chemical and mineralogical stability

Fungal biomasses have emerged as cost-effective biosorbents. To augment their sorptive capabilities, in this study, a novel approach was explored - culturing Aspergillus fungi with magnetite nanopowder, yielding pellet-like biomass structures enclosing the nanoparticles. However, this interaction might induce undesired structural and mineralogical changes in the magnetite nanopowder. Therefore, we investigated the fungal impact on magnetite's structural and chemical stability using powder XRD and Mössbauer spectroscopy. Our findings revealed that the mineralogical alterations induced by A. niger in magnetite nanopowder remained subtle. Intriguingly, despite minimal structural changes in both magnetite (90%) and maghemite (9%), major components revealed by Mössbauer spectroscopy in commercially available magnetite nanopowder, A. niger exhibited remarkable iron extraction (approximately 40%). This highlights its capacity to dissolve magnetite nanopowder while preserving its mineralogical integrity. Conversely, A. clavatus, despite insignificant iron extraction, induced notable crystal lattice distortions in both magnetite and maghemite. This suggests its capacity to trigger structural changes even with limited bioleaching activity. Moreover, we assessed the sorptive performance of the biomass-based composite for arsenic and antimony removal, contributing to a comprehensive understanding of the intricate interaction between fungal biomass and magnetite nanopowder. These findings offer valuable insights into the mineralogical and structural modifications of magnetite induced by fungi and lay the groundwork for designing effective biomass-based sorbents for environmental applications.

Status of X-ray Acoustooptics at the Institute of Microelectronics Technology Russian Academy of Sciences

The electrical measurement method, scanning electron microscopy method and high-resolution X-ray diffraction method have been used to investigate the process of the surface acoustic wave (SAW) propagation in a LiNbO3 ferroelectric crystal. Measurement of the amplitude-frequency response provides information on the losses in the acoustoelectronic device during the process of the SAW propagation. The scanning electron microscopy method permits to visualize the SAW on the surface of piezoelectric crystals in the real-time mode and to observe diffraction phenomena in acoustic beam. The X-ray diffraction method is sensitive to the crystal lattice distortions by surface acoustic wave and allows determining the SAW amplitudes.

Synthesis of lead free hybrid copper halide perovskite nanosheets: Structural and optical properties

The most significant disadvantage of using lead halide perovskite materials in optoelectronic applications is that these materials are toxic. In this work, we report the successful synthesis of copper halide-based hybrid perovskites by exchanging the toxic lead for non-toxic copper metal and investigating the structural and optical properties of the resulting perovskites. At room temperature, using a wet chemical method, the lead-free MACuCl3, MACuCl1.5Br1.5, and MACuBr3 nanosheets were synthesized. It was discovered that a higher concentration of chloride in the copper-based perovskite resulted in a decrease in both the amount of crystal distortion and the volume of the unit cell. The as-synthesized materials have shown attractive absorption features that have been extended to the range of 2 eV. Calculations showed that an increase in the concentration of chloride ions led to a widening of both the direct and indirect optical band gaps. In general, the nanosheets morphology was observed, but when the concentration of bromide ion was raised, rectangular shape was predominant. This work explores the possibilities of using hybrid copper halide perovskite in optoelectronic applications and offers a solution for synthesising the material via simple one-step method.

Manipulation phonon energy for improved thermometric sensitivity of only-core nanoparticles

Luminescent nano thermometry using upconversion nanoparticles (UCNPs) has gained attention in recent years due to its potential advantages over conventional methods. One major challenge in practical applications of nanothermometers is achieving high sensitivity. While efforts have been made to improve the sensitivity of individual core nanoparticles, there are few reports on incorporating phonon energy and local crystal field distortions to improve the sensitivity of only-core upconversion nanoparticles. In this study, we propose a new approach to improve the sensitivity of only-core UCNPs thermometers through phonon tuning and self-photogenic heating. We use the ratio of the intensity of two bands (centered at 520 nm and 540 nm) based on dopant Er3+ as a referenced signal for optical sensing of temperature. We use a host material NaYF4 doped with K+ to produce local crystal field changes at the interface, modifying the phonon energy mode. As the temperature increases, the vibrational mode cannot propagate smoothly along the crystal axis throughout the crystal, disrupting the direction of lattice heat conduction and producing a significant local thermal effect on the nanoscale. This leads to a significant increase in sensitivity, and we achieve an enhanced thermal sensitivity more than twice that of conventional core-only nanoparticles.

Effect of conditions on wet carbonation products of recycled cement paste powder

Wet carbonation is deemed a successful approach to recycling waste concrete powder. Controlling the growth and properties of products in the recycled cement paste powder (CPP) is highly dependent on the wet carbonation conditions. Therefore, this study aims to examine the effect of wet carbonation parameters on wet carbonation products in CPP. The wet carbonation of CPP resulted in mixed distribution of silica gel and CaCO3 without significant layering on the CaCO3. In contrast, silica gel covered the outside of the CaCO3 in the case of dry carbonation. Increasing the temperature from 25 °C to 80 °C promoted and accelerated the crystallization and growth of amorphous CaCO3, increased the crystallite size of CaCO3 by 1.1–5.1 nm, and favored the formation of aragonite and vaterite; however, it also led to a significant crystal defect and/or distortion within CaCO3. Higher temperatures also promoted silica gel formation and increased its polymerization degree by 68.2%. On the other hand, increasing the CO2 flow rate from 3 L/min to 5 L/min facilitated the crystallization and growth of CaCO3 and contributed to the increase in the crystallite size of CaCO3 by 3.0–6.6 nm. Higher CO2 flow led to the incorporation of aluminum into silica gel and resulted in the transformation of its gel pores into capillary pores. The findings of this study contribute to a better understanding of the best experimental parameters to achieve a more efficient and effective concrete waste recycling process.

Gd-doped BiFeO3 crystalline nanofibers for efficient rhodamine B in wastewater removal under simulated sunlight

This work synthesized a series of Gd-doped BiFeO3 (BGFO) hollow nanofibers by electrostatic spinning technique. The wall thickness of the hollow nanofibers was about 100 nm with an average grain size of 20 nm. The crystal structure distortion was found, and the BiFeO3 coexisted with rhombohedral and orthorhombic phases. The degradation efficiency of Gd-doped samples for RhB under simulated sunlight irradiation was higher than that of pure BiFeO3 nanofibers. Among them, the degradation rate of 10BGFO nanofibers on RhB was the fastest and reached 96.3% within 30 min. After five cycles, the removal efficiency could still be maintained at about 90%. The effects of temperatures, ions, concentrations, and water quality on the removal efficiency were studied in detail, and the possible photocatalytic degradation mechanism of BGFO nanofibers was also elaborated. With the increase of Gd doping, the band gap value gradually decreased, and the specific surface area was bigger, which effectively promoted the charge separation and could inhibit the complexation of photogenerated electrons and holes and produced more active substances (·O2-, h+). This study can provide a novel, reusable, flexible photocatalyst to purify dye wastewater.

Study of the synergistic role of multivalence states of 3d cations on the crystal lattice distortion and magnetic behavior of Sr2FeCoO6-δ: A spectroscopic study

In perovskite oxides, the multiple charge states of cations influence their local structure and correlated physical properties. In this report, we studied the role of multivalence cations on the local structure and magnetic behavior of the oxygen-deficient system Sr2FeCoO6-δ (SFCO), prepared by the solid-state synthesis technique. A detailed structural and geometrical analysis confirmed the coexistence of orthorhombic (Brownmillerite) and cubic crystal symmetries and a gesture of the Jahn-Teller (JT) distortion. The intense Raman modes are allowed to be indexed for BO-polyhedra and JT-distortion. Experimental and theoretical analysis of the X-ray photoelectron spectroscopy (XPS) spectra supported the mixed oxidation state of Fe (Fe3+/Fe4+) and Co (Co2+/Co3+), further confirmed by theoretically simulated X-ray absorption spectroscopy (XAS) spectra. The presence of the multivalence states leads to AFM/FM exchange interaction in the sample which further leads to glassy magnetic behavior.

Direct motif extraction from high resolution crystalline STEM images

During the last decade, automatic data analysis methods concerning different aspects of crystal analysis have been developed, e.g., unsupervised primitive unit cell extraction and automated crystal distortion and defects detection. However, an automatic, unsupervised motif extraction method is still not widely available yet.Here, we propose and demonstrate a novel method for the automatic motif extraction in real space from crystalline images based on a variational approach involving the unit cell projection operator. Due to the non-convex nature of the resulting minimization problem, a multi-stage algorithm is used. First, we determine the primitive unit cell in form of two lattice vectors. Second, a motif image is estimated using the unit cell information. Finally, the motif is determined in terms of atom positions inside the unit cell. The method was tested on various synthetic and experimental HAADF STEM images. The results are a representation of the motif in form of an image, atomic positions, primitive unit cell vectors, and a denoised and a modeled reconstruction of the input image. The method was applied to extract the primitive cells of complex μ-phase structures Nb6.4Co6.6 and Nb7Co6, where subtle differences between their interplanar spacings were determined.

Activity enhancement of MgCO3/MgO for thermochemical energy storage by nitrate-promoted and morphology modification

Thermochemical energy storage technology, with its ability to effectively solve the mismatch between energy supply and demand, holds considerable promise. Magnesium carbonate/magnesium oxide (MgCO3/MgO) in particular has shown broad prospects due to its high energy density and trans-regional storage capability. However, pure MgO has limited activity in the exothermic process, with a conversion rate of less than 2%. In this work, activity enhancement of MgCO3/MgO was investigated by combining chemical modification of alkali nitrates and physical morphology regulation. The results indicate that the activation effect of dopants on inert MgO depends on the electronegativity of the cation and the thermal stability of compound dopants. In particular, Na0.5K0.5NO3 with a molar ratio of 1:0.1 promotes MgO carbonation, resulting in a conversion rate of up to 67.5% and an exothermic density of 1964.25kJ/kg at 320°C. The enhanced activity is attributed to the melting of dopants that induces lattice distortion of the perfect crystal, hereby accelerating the chemical reaction. Additionally, the utilization of finely grained rod-like nanocrystalline magnesia precursor with a high specific surface area increased the adsorption capacity. Consequently, the synthesis of mesoporous MgO through the sol–gel method successfully broke through the CO2 adsorption of MgO carrier, achieving a conversion rate of 72.5% and a exothermic density of 2109.75kJ/kg MgO. During 20 release-storage cycles of the MgCO3/MgO TCES carrier, the conversion rate initially degraded significantly and eventually stabilized at approximately 25%. Overall, these methods provide a guiding principle for the preparation of thermochemical energy storage carriers in subsequent applications.