RESUMEN

A designed anthracene-based monomer for topochemical Diels-Alder cycloaddition polymerization crystallized with head-to-tail arrangement of molecules, as revealed by single-crystal X-ray diffraction (SCXRD) analysis. The diene and dienophile units of adjacent monomer molecules are aligned at an average distance of 4.6 Å, suggesting a favorable crystalline arrangement for their intermolecular Diels-Alder cycloaddition reaction to form a linear polymer. Surprisingly, heating the monomer crystals at a temperature above 125 °C resulted in the formation of intramolecular Diels-Alder cycloadduct, which could be characterized by various spectroscopy and SCXRD analysis. Various time-dependent studies such as NMR, PXRD, and DSC, studies established that the reaction followed topochemical pathway. Schmidt's topochemical postulates are generally used to predict the topochemical reactivity and product, by analyzing the crystal structure of the reactant. Though the crystal arrangement predicted polymerization, upon heating, the molecule avoided this pathway by undergoing a large rotation to form an intramolecular cycloadduct. Theoretical calculations supported the feasibility of the rotation, exploiting the flexibility of the molecule and voids present. These findings caution that the reliance on Schmidt's criteria for topochemical reactions may sometimes be misleading, especially in heat-induced reactions.

RESUMEN

The present investigation describes the synthesis of luminescent terbium-doped strontium aluminate nanoparticles emitting bright green light, which were synthesized through a solid-state reaction method assisted by microwave radiation. Various samples containing different concentrations of Tb were synthesized, and an analysis of their structural and morphological features was conducted using powder x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The band gaps of the samples were determined utilizing the Kubelka-Munk method. The quenching mechanism observed was identified to be due to dipole-dipole interaction using the Dexter theory. The optimized sample with a terbium concentration of 4 at.% has a luminescence lifetime of 1.05 ms with 20.62% quantum efficiency. The results of this study indicate that the terbium-doped strontium aluminate fluorescent nanoparticles exhibit promising potential for a wide range of applications, including bioimaging, sensing and solid-state lighting.

Asunto(s)

RESUMEN

In this study, entanglement of composition, additive and/or sintering conditions and their effects on magnetic properties of soft ferrites, nickel zinc spinel ferrites (Ni1-xZnxFe2O4, x = 0.65 and 0.70) which were prepared via conventional solid-state reaction method investigated. Also an equiponderant calcined mixture of Bi2O3, CaO, CeO2, SiO2, Al2O3, Y2O3 and nanotitania was mixed thoroughly and used as a multi-compound calcined additive (MCCA). Calcined ferrite powders were crushed, dry and wet milled, dried, mixed with different amounts of MCCA (0.0, 0.5, 1.0, 1.5 and 2.0 wt%), formed in toroidal shapes and finally sintered at different temperatures, from 1150 up to 1360 °C for 3 h. X-ray diffraction assessment confirmed formation of the single phase cubic spinel structures. Initial permeability and Q-factor spectra of the toroids were obtained from 0.1 to 1000 kHz, using an LCR meter. The results show that initial permeability of each sample has a maximum and addition of MCCA to the ferrites leads to a marvelous increase in permeabilities. Additionally, MCCA decreases the optimum sintering temperature too. The optimum amounts of additive were 1.0 and 0.5 wt% for the x = 0.65 (µ' = 492, Ts = 1280 °C) and x = 0.70 (µ' = 478, Ts = 1320 °C), respectively. Permeability spectra illustrate that utility zone of the Ni0.35Zn0.65Fe2O4 and Ni0.3Zn0.7Fe2O4 are both less than 100 and 10 kHz, respectively. The results represent that there is a strong entanglement between composition, additive and/or sintering conditions. It can be concluded the MCCA added Ni0.35Zn0.65Fe2O4, is suitable for application in the switching power supplies.

RESUMEN

Photochemical valence bond isomerization of a crystalline Dewar benzene (DB) diacid monoanion salt with an acetophenone-linked piperazinium cation that serves as an intramolecular triplet energy sensitizer (DB-AcPh-Pz) exhibits a quantum chain reaction with as many as 450 product molecules per photon absorbed (Φ ≈ 450). By contrast, isomorphous crystals of the DB diacid monosalt of an ethylbenzene-linked piperazinium (DB-EtPh-Pz) lacking a triplet sensitizer showed a less impressive quantum yield of ca. Φ ≈ 22. To establish the critical importance of a triplet excited state carrier in the adiabatic photochemical reaction we prepared mixed crystals with DB-AcPh-Pz as a dilute triplet sensitizer guest in crystals of DB-EtPh-Pz. As expected from their high structural similarities, solid solutions were easily formed with the triplet sensitizer salt in the range of 0.1 to 10%. Experiments carried out under conditions where light is absorbed by the triplet sensitizer-linked DB-AcPh-Pz can be used to initiate a triplet state adiabatic reaction from 3DB-AcPh-Pz to 3HB*-AcPh-Pz, which can serve as a chain carrier and transfer energy to an unreacted DB-EtPh-Pz where exciton delocalization in the crystalline solid solution can help carry out an efficient energy transfer and enable a quantum chain employing the photoproduct as a triplet chain carrier. Excitation of mixed crystals with as little as 0.1% triplet sensitizer resulted in an extraordinarily high quantum yield Φ ≈ 517.

RESUMEN

A large-scale quantity of copper oxalate nanoparticles were successfully obtained via a facile and green solid-state chemical reaction. Copper oxalate nanoparticles were obtained by ball-milling between copper chloride, Liquorice (Glycyrrhiza glabra), and ascorbic acid at ambient conditions. The size and morphology of copper oxalate nanoparticles powder were studied by transmission and scanning electron microscopy. The prepared nanoparticles were semi-spherical in shape and ranged from 5 to 15 nm in size. UV/Vis spectroscopy, Fourier transforms infrared spectroscopy, and X-ray photoelectron spectroscopy measurements were carried out to characterize the prepared samples. Copper oxalate nanoparticles were evaluated as a catalyst in the catalytic degradation of 4-nitrophenol, bromophenol blue, reactive yellow, and a mixture of the three pollutants. The present study combined solid-state reaction and green requirements for the mass production of nanomaterials. The proposed reaction is performed in simple steps, inexpensive, low energy consuming, solvent-free, and minimizes the emission of secondary wastes.

Asunto(s)

RESUMEN

In the present work, we studied the impact of excess Na addition on the structure of the standard NASICON ion conductor along with Na ion transport mechanisms. In this sense, NASICON ceramic membranes (NZSP) were prepared by a simple chemical synthesis method, the solid state reaction (SSR), using an excess of 5% Na (Na3.15Zr2Si2PO12) and an excess of 10% Na (Na3.3Zr2Si2PO12), in order to improve the conduction properties of the ceramic membrane. The characterization of the NZSP nanoparticles was performed by measuring the particle size by dynamic light scattering (DLS), the morphology of the NASICON samples pre-sintered at 1100 °C was analyzed by the SEM method (scanning electron microscope), and X-ray diffraction (XRD) analysis was used to investigate the crystal structure of samples, while the surface area was measured using the BET technique. The electrical properties (i.e., ionic conductivity) were evaluated by impedance spectroscopic methods at room temperature (RT). Following the experiments for NASICON membranes without Na excess, with 5% Na excess, and with 10% Na excess synthesized at different pressing forces and sintering temperatures, it was found that membranes with a 10% Na excess, sintered at 1175 °C for 10 h, presented a good ionic conductivity (4.72 × 10-4 S/cm).

RESUMEN

High-entropy oxides (HEOs) are promising anode materials for lithium-ion batteries (LIBs), owing to their stable crystal structure, superionic conductivity, and high capacity. In this study, the (Cr, Mn, Fe, Co, and Ni)3O4 HEO via solid-state reaction is prepared. To improve the synthetic efficiency, it is necessary to understand the formation mechanism. Therefore, a high-resolution transmission electron microscopy (HRTEM) is used to record information during calcination at increasing temperature. The overall formation process included MnO2 and NiO aggregation at 500 °C, followed by (Mn, and Ni)3O4 combined with Co3O4 at 600 °C to form (Mn, Co, and Ni)3O4. At higher temperatures, Fe2O3 and Cr2O3 sequentially combined with (Mn, Co, and Ni)3O4 and formed the (Cr, Mn, Fe, Co, Ni)3O4 at 900 °C. In addition, the valence-state-changing mechanisms and ion arrangements of (Cr, Mn, Fe, Co, and Ni)3O4 are determined using electron energy loss spectroscopy (EELS) and extended X-ray absorption fine structure (EXAFS). This study successfully revealed the formation of HEO at atomic scale. The results provide valuable insights for improving the manufacturing process of (Cr, Mn, Fe, Co, and Ni)3O4 HEOs, which is expected to play a vital role in the development of anode materials for next-generation LIBs.

RESUMEN

GaAs nanowires are promising candidates for emerging devices in a broad field of applications (e.g., nanoelectronics, photodetection, or photoconversion). These nanostructures benefit greatly from a vertical integration, as it allows for the exhibition of the entire nanowire surface. However, one of the main challenges related to vertical integration is the conception of an efficient method to create low resistive contacts at nanoscale without degrading the device performance. In this article, we propose a complementary metal-oxide-semiconductor (CMOS)-compatible approach to form alloyed contacts at the extremities of vertical GaAs nanowires. Ni-based and Pd-based alloys on different vertical GaAs nanostructures have been characterized by structural and chemical analyses to identify the phase and to study the growth mechanisms involved at the nanoscale. It is shown that the formation of the Ni3GaAs alloy on top of nanowires following the epitaxial relation Ni3GaAs(0001)∥GaAs(111) leads to a pyramidal shape with four faces. Finally, guidelines are presented to tune the shape of this alloy by varying the initial metal thickness and nanowire diameters. It will facilitate the fabrication of a nanoalloy structure with tailored shape characteristics to precisely align with a designated application.

RESUMEN

The phase equilibria of the Ag-Al-Au ternary system and the solid-state reaction couple for the Au-xAg/Al system were investigated isothermally at 450 °C. By investigating the Ag-Al-Au ternary system and its isothermal section, this study aims to provide a clearer understanding of the phase stability and interfacial reactions between different phases. This information is crucial for designing materials and processes in electronic packaging, with the potential to reduce costs and improve reliability. There were seven single-phase regions, thirteen two-phase regions, and six three-phase regions, with no ternary intermetallic compound (IMC) formed in the isothermal section of the Ag-Al-Au ternary system. When the Au-25 wt.% Ag/Al couple was aged at 450 °C for 240-1500 h, the AuAl2, Au2Al, and Au4Al phases formed at the interface. When the Ag contents increased to 50 and 75 wt.%, the Ag2Al, AuAl2, and Au4Al phases formed at the interface. When the aging time increased from 240 h to 1500 h, the total IMC thickness in all Au-xAg/Al couples became thicker, but the types of IMCs formed at the interface did not change. The total IMC thickness also increased with the increase in the Ag content. When the Ag content was greater than 25 wt.%, the Au2Al phase was converted into the Ag2Al phase. The IMC growth mechanism in all of the couples followed a reaction-controlled process.

RESUMEN

BaMoO4 was obtained via facile mechanochemical synthesis at room temperature and a solid-state reaction. An evaluation of the phase composition and structural and optical properties of BaMoO4 was conducted. The influence of different milling speeds on the preparation of BaMoO4 was explored. A shorter reaction time for the phase formation of BaMoO4 was achieved using a milling speed of 850 rpm. A milling speed of 500 rpm led to partial amorphization of the initial reagents and to prolongation of the synthesis time of up to 3 h of milling time. Solid-state synthesis was performed via heat treatment at 900 °C for 15 h. X-ray diffraction analysis (XRD), infrared (IR) and UV diffuse reflectance (UV-Vis) and photoluminescence (PL) spectroscopy were carried out to characterize the samples. Independently of the method of preparation, the obtained samples had tetragonal symmetry. The average crystallite sizes of all samples, calculated using Scherrer's formula, were in the range of 240 to 1540 Å. IR spectroscopy showed that more distorted structural MoO4 units were formed when the compound was synthesized via a solid-state reaction. The optical band gap energy of the obtained materials was found to decrease from 4.50 to 4.30 eV with increasing crystallite sizes. Green- and blue-light emissions were observed for BaMoO4 phases under excitation wavelengths of 330 and 488 nm. It was established that the intensity of the PL peaks depends on two factors: the symmetry of MoO4 units and the crystallite sizes.

RESUMEN

The influences of ethylene-based elastomer (EE) and the compatibilizer agent ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) on the thermal degradation of PLA/EE blends were evaluated by the thermal degradation kinetics and thermodynamic parameters using thermogravimetry. The presence of EE and EBAGMA synergistically improved the PLA thermal stability. The temperature of 10% of mass loss (T10%) of PLA was around 365 °C, while in the compatibilized PLA/EE blend, this property increased to 370 °C. The PLA average activation energy (Ea¯) reduced in the PLA/EE blend (from 96 kJ/mol to 78 kJ/mol), while the presence of EBAGMA in the PLA/EE blend increased the Ea¯ due to a better blend compatibilization. The solid-state thermal degradation of the PLA and PLA/EE blends was classified as a D-type degradation mechanism. In general, the addition of EE increased the thermodynamic parameters when compared to PLA and the compatibilized blend due to the increase in the collision rate between the components over the thermal decomposition.

RESUMEN

Lithium-sulfur (Li-S) batteries have been investigated intensively as a post-Li-ion technology in the past decade; however, their realizable energy density and cycling performance are still far from satisfaction for commercial development. Although many extremely high-capacity and cycle-stable S cathodes and Li anodes are reported in literature, their use for practical Li-S batteries remains challenging due to the huge gap between the laboratory research and industrial applications. The laboratory research is usually conducted by use of a thin-film electrode with a low sulfur loading and high electrolyte/sulfur (E/S) ratios, while the practical batteries require a thick/high sulfur loading cathode and a low E/S ratio to achieve a desired energy density. To make this clear, the inherent problems of dissolution/deposition mechanism of conventional sulfur cathodes are analyzed from the viewpoint of polarization theory of porous electrode after a brief overview of the recent research progress on sulfur cathodes of Li-S batteries, and the possible strategies for building an electrochemically stable sulfur cathode are discussed for practically viable Li-S batteries from the authors' own understandings.

RESUMEN

This study presents a method for solvent-free mechanochemical synthesis of chitosan from chitin, sourced from the shells of mud crabs (Scylla serrata). The procedure involves a sequence of demineralization and deproteinization to extract chitin from the crab shells, followed by mechanochemical deacetylation. The chitin was deacetylated by grinding it as a solid blend with sodium hydroxide (NaOH) using a stainless steel mortar and pestle. After grinding, chitosan is isolated from the blend by repetitive washing and centrifugation. The chitosan product is then characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. These characterization techniques confirm the successful deacetylation of chitin to form chitosan. A high degree of deacetylation (DD) is achieved when the weight ratio of NaOH to chitin is 1:1 or higher, implying that the DD value can be enhanced by increasing this weight ratio. The mechanochemical reaction mechanism involves the hydroxyl groups on the NaOH particles reacting with the acetamide groups of the chitin strands, yielding solid chitosan and sodium acetate. This mechanochemical deacetylation approach is more practical than the conventional heterogeneous deacetylation in strong basic solutions, since it could suppress depolymerization of the resulting chitosan and requires significantly less base. This makes it a promising method for large-scale industrial applications.

Asunto(s)

RESUMEN

The crystal structure of a commercially available anthracene derivative, anthracene-9-thiocarboxamide, is reported here for the first time. The compound undergoes a [4+4] cycloaddition in the solid state to afford facile synthesis of the cycloadduct (CA). The cycloaddition is also reversible in the solid state using heat or mechanical force. Due to the presence of unpaired, strong hydrogen-bond donor atoms on the CA, significant solvatomorphism is achieved, and components of the solvatomorphs self-assemble into four different classes of supramolecular structures. The CA readily crystallizes with a variety of structurally-diverse solvents including those containing oxygen-, nitrogen-, or pi-acceptors. Some of the solvents the CA crystallized with include thiophene, benzene, and the three xylene isomers; thus, the CA was employed in industrially-relevant solvent separation. However, in competition studies, the CA did not exhibit selectivity. Lastly, it is demonstrated that the CA crystallizes with vinyl-containing monomers and is currently the only compound that crystallizes with both widely used monomers 4-vinylpyridine and styrene. Solid-state complexation of the CA with the monomers affords over a 50 °C increase in the monomer's thermal stabilities. The strategy of designing molecules with unused donors can be applied to achieve separations or volatile liquid stabilization.

RESUMEN

Ferroelectric materials with crystal symmetry transition from single phase to multiphase coexistence exhibit anomalous photosensitive properties. The optical properties (optical band gap and photosensitive) found on non-centrosymmetric and centrosymmetric systems achieved research interest because of their interesting behavior. In this regard, the lead-free polycrystalline Ba1-xSrxTiO3(BSTO, 0⩽x⩽0.3) has been synthesized to explore its crystal structure, dielectric, light absorption, and photocurrent sensing properties for various applications. Both experimental and theoretical studies on BSTO (0⩽x⩽0.3) ceramics confirm the crystal symmetry transition with the reduction of band gap as compared to pristine BaTiO3. This crystal symmetry transition plays an important role in varying the various physical properties as it involves the transition from the polar phase to the non-polar phase. The optical band gap has been estimated experimentally by the Tauc plot method and found that there is a small variation of energy band gap from 3.615 eV to 3.212 eV with Sr substitution. The highest dielectric constant was found to be 5327 at lower frequency on Ba0.76Sr0.24TiO3after that for further increase in Sr concentration the dielectric constant decreases because of the introduction of the non-polar phase. A strong correlation between crystal structure and physical properties (dielectric, optical, etc.) has been observed. The photocurrent of the samples is significant which reveals that the sample is influenced by the photons. In a nutshell, the present study deepens the understanding of the correlation between crystal structure and various physical properties of BSTO and, hence provides an idea of required design parameters to construct a ferroelectric system for better photosensitive nature suitable for device applications.

RESUMEN

Ni-xCu/Sn soldering joints were aged at 200 °C, and the microstructure evolution and mechanical properties during the solid-state reaction were studied under shear loading. Results showed that the intermetallic compounds (IMCs) exhibited a Cu content-dependent transformation from the (Ni,Cu)3Sn4 phase to the (Cu,Ni)6Sn5 phase at the Ni-xCu/Sn interface. Furthermore, a Cu3Sn layer was observed exclusively at the Cu/Sn interface. The shear strength of the soldering joints after thermal aging exhibited an initial decrease followed by an increase, except for a significant enhancement at the Cu content of 60 wt.%. In addition, the evolution law of mechanical properties and failure mechanism of the thermal aging joints were elucidated based on the fracture microstructure and the fracture curve of the joints.

RESUMEN

The current study involves the synthesis and characterisation of europium doped strontium aluminate nanophosphors using the solid-state reaction method with varying concentrations of europium. The existence of the SrAl2O4 phase in all samples was verified using X-ray diffraction and FTIR analysis. The lattice parameters as well as phase fractions were determined using Rietveld refinement. Surface morphology was studied using field emission scanning electron microscope. Using the Tauc plot method acquired from the diffuse reflectance spectra, the band gaps of the samples were determined and it was found that the doped samples possess lower band gaps compared to the host. Our findings demonstrate that these nanophosphors exhibiting bright orange-red emission under UV excitation with quantum efficiency 70.68%, can be applied for display and fluorescence imaging.

RESUMEN

Rare earth luminescent materials demonstrate significant advantages in lighting and energy saving, and detection etc. In this paper, a series of Ca2Ga2(Ge1-xSix)O7:y%Eu2+ phosphors were synthesized by high-temperature solid-state reaction and characterized by X-ray diffraction and luminescence spectroscopy methods. The powder X-ray diffraction patterns reveal that all the phosphors are isostructural with a space group of P4¯21m. The excitation spectra of Ca2Ga2(Ge1-xSix)O7:1%Eu2+ phosphors exhibit significant overlapping of the host and the Eu2+ absorption bands, which facilitates Eu2+ absorbing the energy to increase its luminescence efficiency when excited by visible photons. The emission spectra show that the Eu2+ doped phosphors have a broad emission band with a peak centered at 510 nm arising from the 4f65d1→4f7 transition. Variable temperature fluorescence reveals that the phosphor has a strong luminescence at low temperature but has a severe thermal quenching effect when temperature rises. The optimal Ca2Ga2(Ge0.5Si0.5)O7:1.0%Eu2+ phosphor shows promise for application in the field of fingerprint identification based on the experimental results.

RESUMEN

Solid solutions (1-x-y)(Na0.5Bi0.5)TiO3-xBaTiO3-y(K0.5 Bi0.5)TiO3 with (x (mol.%) = 0, 7 and 100); y(mol.%) = 0, 20 and 100) compositions have been prepared by a conventional solid-state reaction method, and their structure, dielectric properties and depolarization temperature have been examined. At room temperature, X-ray diffraction (XRD) patterns reveal that the crystalline structure of the ceramics was perovskite. The morphotropic phase boundary (MPB) of the ternary system lying between rhombohedral (R3c) and tetragonal (P4mm) phases is in the range of (x (mol.%) = 7 and y (mol.%) = 20). The Raman-active modes for 0.73NBT-0.07BT-0.20KBT were separated and identified under the framework of group theory. SEM micrographs illustrate the quasi-uniform distribution of the grains, which are compact. The dielectric properties of the ceramics were studied in the frequency range of 1 kHz-100 kHz from ambient temperature to 600 °C. Dielectric measurements indicate that all ceramics show a diffuse phase transition near the temperature (Tm) for diffusivity of the order of 1.4-1.7 and a shift of (Tm) towards high temperatures. The resistance and capacitance of the various contributors (grain and grain boundary) in our samples are also discussed using a brick-layer model. Excellent piezoelectric properties for d33 = 146 pCN-1 and electromechanical coupling factors kp = 29.4% were observed at morphotropic phase boundary (MPB), which was assumed to be associated with the coexistence of rhombohedral and tetragonal phases and accurate grain size. This work establishes a new approach for improving lead-free piezoelectric ceramics based on 0.73NBT-0.07BT-0.20KBT.

RESUMEN

In this work, isothermal sections of the Ln2O3-Cr2O3-B2O3 (Ln = Gd-Lu) ternary oxide systems at 900, 1000, and 1100 °C were constructed by determining the phase relations by using a powder X-ray diffraction technique. As a result, these systems were divided into subsidiary subsystems. Two types of double borates, LnCr3(BO3)4 (Ln = Gd-Er) and LnCr(BO3)2 (Ln = Ho-Lu), were observed in the investigated systems. Regions of phase stability for LnCr3(BO3)4 and LnCr(BO3)2 were determined. It was shown that the LnCr3(BO3)4 compounds crystallized in rhombohedral and monoclinic polytype modifications up to 1100 °C; above this temperature and up to the melting points, the monoclinic modification was predominantly formed. The LnCr3(BO3)4 (Ln = Gd-Er) and LnCr(BO3)2 (Ln = Ho-Lu) compounds were characterized by using a powder X-ray diffraction method and thermal analysis.