Preferred Orientation Research Articles

Link between b.c.c.-f.c.c. orientation relationship and austenite morphology in CF8M stainless steel.

Slow-cooled CF8M duplex stainless steel is used for critical parts of the primary coolant pipes of nuclear reactors. This steel can endure severe service conditions, but it tends to become more brittle upon very long-term aging (tens of years). Therefore, it is essential to understand its specific microstructure and temporal evolution. As revealed by electron backscatter diffraction (EBSD) analyses, the microstructure consists of millimetre-scale ferritic grains within which austenite lath packets have grown with preferred crystallographic orientations concerning the parent ferritic phase far from the ferrite grain boundaries. In these lath packets where the austenite phase is nucleated, the lath morphology and crystal orientation accommodate the two ferrite orientations. Globally, the Pitsch orientation relationship appears to display the best agreement with the experimental data compared with other classical relationships. The austenite lath packets are parallel plate-shaped laths, characterized by their normal n. A novel methodology is introduced to elucidate the expected relationship between n and the crystallographic orientation given the coarse interfaces, even though n is only partly known from the observation surface, in contrast to the 3D crystal orientations measured by EBSD. The distribution of retrieved normals n is shown to be concentrated over a set of discrete orientations. Assuming that the ferrite and austenite obey the Pitsch orientation relationship, the determined lath normals are close to an invariant direction of the parent phase given by the same orientation relationship.

An Effect of Al on the Properties of ZnIn2Se4 Thin Film

Abstract Zinc-indium-selenide ZnIn2Se4 (ZIS) ternary chalcopyrite thin film on glass with a 500 nm thickness was fabricated by using the thermal evaporation system with a pressure of approximately 2.5×10−5 mbar and a deposition rate of 12 Å/s. The effect of aluminum (Al) doping with 0.02 and 0.04 ratios on the structural and optical properties of film was examined. The utilization of X-ray diffraction (XRD) was employed to showcase the influence of aluminum doping on structural properties. XRD shows that thin ZIS-pure, Al-doped films at RT are polycrystalline with tetragonal structure and preferred (112) orientation. Where the degree of crystallinity is raised. The effect of Al content on surface roughness and average diameter was studied by atomic force microscopy (AFM), which showed that both surface roughness and average diameter increased with an increasing Al ratio until they reached their maximum values of 12.93 nm and 61.56 nm, respectively. Optical characteristics of ZIS thin film and the impact of aluminum on optical parameters have been investigated, and it was found that the optical energy ( E g opt ), absorption coefficient (α), extinction coefficient (k), refractive index (n), both the real (εr) and imaginary (εi) components of the dielectric constant have values of (1.8 eV), (3.11×104 cm−1), (0.111), (2.3), (5.36), and (0.517), respectively, for ZIS thin films at an Al ratio equal to 0.04.

Deformation anisotropy and lamellar α re-orientation of TC17 alloy under the different slip modes of HCP structure

Deformation anisotropy and re-orientation for α phase during isothermal compression of TC17 alloy with basketweave microstructure were investigated systematically by quantitative analysis the influence of tilt angle between compression axis and c-axis on LABs density, rotate factor and ratio of activated slip system. The test results revealed that the tilt angle between compression axis and c-axis affects the deformability of α grain by affecting the rotation tendency and the number of activated slip systems. It results in the different prone of lamellar α with different orientation to globularization. Therein, the variation of the rotation factor with tilt angle conforms to the quadratic function, reaching a maximum value around 45°. When the rotation factor is small, the ratio of (01–11) [1–210] slip system with small Burgers vector at the phase boundary is large, the rotation tendency is poor, and the intragranular dislocation slip replaces the grain rotation as the strain accommodation mechanism, the lamella is more prone to globularization. And when the tilt angles are between 0°–13°, 13°–35°, 35°–78° and 78°–90°, the most easily activated slip systems are pyramidal <a+c> slip, basal <a> slip, pyramidal <a> slip and prismatic <a> slip, respectively. The more slip systems may be activated, the lamella is more prone to globularization. In addition, isothermal compression destroys the initial preferred orientations of the α grains and causes the lamellar α to rotate towards the direction that forms (0 0 0 1) plane texture, which is formed due to the activation of the prismatic <a> slip. Then, the (0 0 0 1) plane texture will be weakened due to a large number of randomly oriented grains generated by recrystallization under larger height reduction.

Effects of cold rolling path on recrystallization behavior and mechanical properties of pure copper during annealing

The recrystallization behavior, grain boundary characteristic distribution, and mechanical properties of pure Cu sheets that were subjected to different cold rolling paths, and then annealed at 400 °C for 10, 30, 60, and 420 min, were investigated. Different rolling paths changed the grain boundary orientations of cold-rolled copper, causing recrystallized grains to nucleate and grow in an oriented manner. However, the evolution of the texture indicated that cold-rolled copper with different rolling paths did not show an obvious preferred orientation after annealing. The RD-60 specimen exhibited the smallest grain size (6.6 μm). The results indicated that the grain size and low-Σ CSL grain boundaries worked together to provide RD-60 samples with appropriate mechanical properties and high plasticity. The yield strength, ultimate tensile strength, and elongation of RD-60 sample were 81 MPa, 230 MPa, and 49%, respectively. These results could provide guidance for tuning the microstructures and properties of pure Cu foils, as well as designing fabrication routes for pure Cu foils through processes such as rolling and drawing.

The influence of nitrogen content on the microstructure and properties of W-Ta-Cr-V-N refractory high-entropy nitrides

To enhance the mechanical performance and corrosion resistance of refractory high-entropy alloys (RHEAs) and to identify materials better suited for severe high-temperature and corrosive environments, this study utilized a double glow plasma surface alloying technique to fabricate a W-Ta-Cr-V-N refractory high-entropy nitride coating on a W substrate. The microstructure and phase structure of the samples were characterized using a scanning electron microscope and X-ray diffractometer. The mechanical properties of the samples were evaluated through microhardness testing, while their corrosion performance was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The study investigated the effects of different nitrogen contents on the microstructure, mechanical properties, and corrosion resistance of the BCC-structured W-Ta-Cr-V alloy in the past tense. The study found that the doping of an appropriate amount of nitrogen can lead to the formation of FCC and HCP structured nitrides. As the nitrogen content increases, there is a significant change in the preferred orientation of the coating. When the nitrogen content is 16.6 at.%, the distribution of the nitrides is uneven, resulting in increased surface undulations and roughness. Conversely, when the nitrogen content is elevated to 48.1 at.%, the clustering of surface nitride particles becomes more pronounced, leading to a decrease in the coating density. The thickness of the nitride coatings is around 10 μm, with a slight decrease in thickness as the nitrogen content increases. The hardness of the coatings is significantly superior to that of the W-Ta-Cr-V alloy films, reaching up to 3465 HV0.25 in the highest instance. The introduction of 31.4 at.% nitrogen results in the densest coating, effectively enhancing the corrosion resistance of the refractory high-entropy alloy. Therefore, the doping of an appropriate amount of nitrogen can alter the microstructure of the refractory high-entropy alloy, improve its mechanical properties, and enhance its chemical stability.

Pr2CuO4/MWCNT/MXene/PANI: A novel quaternary composite with tunable properties for potential applications in optoelectronics and energy storage devices

Pr2CuO4/MXene/MWCNT and PANI composites were synthesized for symmetric supercapacitor applications using a simple hydrothermal and in-situ polymerization technique. Pr2CuO4/ MXene/MWCNT and PANI were of ratios 40:60 (PC1), 50:50 (PC2), and 60:40 (PC3). Composites had a tetragonal single phase of Pr2CuO4 with a preferred orientation peak along (103) plane. FTIR confirmed functional bands of all constituents of the composite. Porous morphology was confirmed by scanning electron microscopy (SEM) beneficial for energy storage capacity. The PC2 Composite possessed the widest absorption range and the smallest band gap energy. The dielectric constant of PC2, was the highest than pure Pr2CuO4 and the other composites. Coercivity and saturation magnetization for the composites decreased with decreasing Pr2CuO4 percentage, producing less eddy currents, which reduced energy dissipation and contributed to the increased efficiency of capacitors and inductors. The best ratio of Pr2CuO4/ MXene/MWCNT and PANI was 50:50 for increasing rate capability. This ratio enhanced surface area, charge storage capacity, specific capacity, and impedance behaviour. The optimized PC2 (Pr2CuO4/MXene/MWCNT: PANI 50:50) electrode exhibited exceptional electrochemical performance, achieving volumetric and gravimetric capacitance values of 2611.47 Fg−1 at 2 Ag−1. This enhanced performance can be explained by the combined effects of Pr2CuO4/MWCNT/PANI, which actively promoted pseudocapacitance and impeded MXene restacking. An excellent candidate for advanced energy storage systems, the electrode has an energy density of 58.032 Whkg−1 and remarkable rate capabilities.

Crystallographic Preferred Orientation of Phase D at High Pressure and Temperature: Implications for Seismic Anisotropy in the Mid‐Mantle

AbstractSeismic anisotropy has been widely observed in the lower mantle transition zone and the uppermost lower mantle near several subducting slabs, which is typically attributed to the crystallographic preferred orientation (CPO) of constituent minerals. In this study, well‐controlled uniaxial and simple shear deformation experiments were conducted on Mg‐endmember phase D and Al‐bearing phase D aggregates at 20 GPa and 500–1,000°C. Strong (0001) fabrics were observed in the uniaxially compressed samples. The CPO from all experiments, including extension and simple shear, indicated that the most active slip systems in phase D were &lt;110&gt;(0001) and &lt;100&gt;(0001), with a dominance of &lt;110&gt;(0001). The calculated seismic velocity suggests that the deformed phase D generates positive radial seismic anisotropy (VSH &gt; VSV) in both subhorizontal shearing and subvertical compression, causing significant shear‐wave splitting time. Our results suggest that the observed seismic anisotropy in the mid‐mantle in several cold subduction zones can be well explained by the presence of deformed phase D.

Investigation of the Annealing and Cu Doping Effect on Structural and Optical Properties of CdZnS Nanomaterial Deposited by Ultrasonic Spray Pyrolysis

This study investigates doped CdZnS thin films synthesized through the ultrasonic spray pyrolysis technique, followed by annealing at temperatures of 400 and 500 °C. X-ray diffraction analysis demonstrated that both undoped CdZnS and Cu-doped CdZnS thin films exhibit cubic crystal structures, with a preferred orientation along the (111) plane. Scanning electron microscopy (SEM) measurements indicated that the CdZnS thin film has a smooth surface, whereas the Cu-doped CdZnS film shows clustered particles, attributed to the effect of copper doping acting as an activator metal ion. Electron dispersive scanning (EDS) analysis confirmed that the Cd, Zn, and S elements are present in acceptable chemical stoichiometry (Cd + Zn/S = 1:1), with a ratio of 3:1, consistent with the molar amounts used in the precursor solutions. The band gap of the CdZnS thin film decreased from 3.12 to 2.56 eV after annealing at 500 °C, attributed to an increase in crystal size. In contrast, the band gap of the Cu-doped CdZnS thin film decreased from 2.51 to 2.22 eV, lower than that of pure CdZnS, due to the formation of additional phases such as zinc oxide and copper oxide within the CdZnS host structure during annealing.

Constraining the Excessive Aggregation of Non-Fullerene Acceptor Molecules Enables Organic Solar Modules with the Efficiency >16.

Translating high-performance organic solar cell (OSC) materials from spin-coating to scalable processing is imperative for advancing organic photovoltaics. For bridging the gap between laboratory research and industrialization, it is essential to understand the structural formation dynamics within the photoactive layer during printing processes. In this study, two typical printing-compatible solvents in the doctor-blading process are employed to explore the intricate mechanisms governing the thin-film formation in the state-of-the-art photovoltaic system PM6:L8-BO. Our findings highlight the synergistic influence of both the donor polymer PM6 and the solvent with a high boiling point on the structural dynamics of L8-BO within the photoactive layer, significantly influencing its morphological properties. The optimized processing strategy effectively suppresses the excessive aggregation of L8-BO during the slow drying process in doctor-blading, enhancing thin-film crystallization with preferential molecular orientation. These improvements facilitate more efficient charge transport, suppress thin-film defects and charge recombination, and finally enhance the upscaling potential. Consequently, the optimized PM6:L8-BO OSCs demonstrate power conversion efficiencies of 18.42% in small-area devices (0.064 cm2) and 16.02% in modules (11.70 cm2), respectively. Overall, this research provides valuable insights into the interplay among thin-film formation kinetics, structure dynamics, and device performance in scalable processing.

Advancements in lithium zinc phosphate (LZP) nanoparticles: Enhanced electrochemical performance for high-efficiency supercapacitors

The synthesized LiZnPO4 nanoparticles were characterized at different temperatures like (400oC, 500 °C, 600 °C, and 700 °C) using various techniques including XRD, FTIR, FESEM, XPS, and electrochemical analyses. X-ray diffraction (XRD) analysis of LiZnPO4 nanoparticles sintered at temperatures from 400 to 700 °C revealed well-crystallized structures at 700 °C, with preferred orientations along (202) and (020) planes. The Scherrer formula was employed to determine crystallite sizes, showing an increase from 55 nm at 400 °C to 85 nm at 700 °C. The annealing temperature influences the formation of microspherical aggregates, determining their surface area and thereby affecting energy storage performance. Samples annealed at 700 °C exhibited a specific capacitance of approximately 268 F/g at a current density of 0.5 A/g and scan rate of 5 mV/s. Our studies indicate that LiZnPO4-based nanostructures have substantial potential for the development of hybrid supercapacitors.

Effects of off-axis angles of 4H-SiC substrates on properties of β-Ga2O3 films grown by low-pressure chemical vapor deposition

In this work, β-Ga2O3 films with (−201) preferred orientation were heteroepitaxially grown on SiC substrates with off-axis angles of 0°, 4° and 8° by low-pressure chemical vapor deposition (LPCVD). It is found that the crystal quality, surface morphology, electrical properties of the β-Ga2O3 films of the film are significantly sensitive to the off-axis angle of SiC substrates. The crystal quality and surface morphology of the film were significantly improved when the 4° off-axis substrate was used, of which the FWHM (Full width at half maximum) was as low as 0.169° and the Ra (Roughness Average) of the smooth surface was 1.98 nm. Due to the improvement of crystal quality, the Hall mobility of the films deposited on 4° off-axis substrates was increased to 50.88 cm2/V·s. The photoluminescence peak intensity of the film increases first and then decreases with the increase of the off-axis angle of the substrate. However, the use of the off-axis substrate has no obvious effect on the oxygen vacancy ratio of the films. The results of this study demonstrate the significance for the preparation of high quality heteroepitaxial β-Ga2O3 films on SiC substrate for the promising applications in power electronic and optoelectronic devices.

Microstructural and properties investigations of tantalum-doped tungsten diboride ceramic coatings via HiPIMS and RF magnetron sputtering

In this work, tantalum-doped tungsten boride ceramic coatings were deposited from a single sputtering target with the radio frequency (RF) and high-power impulse magnetron sputtering (HiPIMS) methods. Two-inch torus targets were synthesised from pure elements with the spark plasma sintering (SPS) method with a stoichiometric composition of W1-xTaxB2.5 (x = 0, 0.08, 0.16, 0.24). Films were deposited with RF and HiPIMS power suppliers at process temperatures from RT to 600 °C. The substrate heating and the energy of the ionised material impacting the substrate increase the surface diffusivity of adatoms and are crucial in the deposition process. The results of SEM and XRD investigations clearly show that the addition of tantalum also changes the microstructure of the deposited films. The coatings without tantalum possess a finer microstructure than those with 24% of tantalum. The structure of films is homogeneous along the film thickness and composed mainly of columns with a (0001) preferred orientation. Deposited coatings are composed mainly of P6/mmm α-WB2 structures. The analysis of nanoindentation results allowed us to determine that ceramic coatings obtained with the HiPIMS method possess hardness above 41 GPa and a ratio of hardness to reduced Young modulus above 0.1. The thickness of HiPIMS-deposited films is relatively small: only around 60% of the RF magnetron sputtered coatings even when the average power input was two times higher. However, it has been shown that the RF coatings require heating the substrate above 400 °C to obtain a crystalline structure, while the HiPIMS method allows for a reduction of the substrate temperature to 300 °C.

Influence of TiC particle size on microstructural evolution and fracture mechanism of TiC/Al-Cu composites

Using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and molecular dynamics simulations, this work investigated the microstructure, texture evolution, strengthening mechanisms, and fracture progression of TiC/Al-Cu composites with various particle sizes following hot extrusion and heat treatment. TiC particles significantly refine grain sizes, shifting the dominant coincidence site lattice (CSL) boundaries from Σ5 to Σ3. The addition of TiC particles alters the preferred grain orientation from (111)/ED to (001)/ED, and modifies the type and intensity of the texture. The primary strengthening mechanisms attributed to TiC include grain boundary strengthening, dislocation strengthening, Orowan strengthening, and load transfer strengthening. However, the strong tendency of smaller TiC particles to agglomerate substantially diminishes these strengthening effects; thus, under a TiC addition of 0.5 wt%, larger TiC particles exhibit better mechanical properties. Fractographic analysis and molecular dynamics simulations revealed that microcracks originate from dissociation at the interfaces between the TiC agglomerates and the Al matrix. The subsequent propagation, expansion, and interconnection of multiple crack initiation sites lead to the formation of macroscopic cracks that result in material failure.

Physical properties of La:ZnO thin films prepared at different thicknesses using spray pyrolysis technique

Herein we investigate the impact of film thickness on the physical properties of Lanthanum (La) doped ZnO thin films. The films were fabricated using the spray pyrolysis technique with a consistent La content of 5 weight (wt) % in the initial solution. X-ray diffraction analysis indicated the presence of a hexagonal ZnO phase with preferred orientation along the (002) direction and no other phases were detected. The crystallite sizes were calculated using the Halder-Wagner equation, with a maximum size of 16.1 nm observed for a film thickness of 106 nm. Field-emission scanning electron microscopy (FE-SEM) images revealed the formation of a continuous film with an average grain size that increased as the thickness of the film increased. The grain size ranged from 74.5 to 136 nm as the film thickness varied from 106 to 426 nm. Films with lower thicknesses up to 196 nm exhibited two band gaps at approximately 3.2 and 4 eV, while films with higher thicknesses displayed a single band gap around 3.2 eV. The refractive index dispersion for all films was modeled using the Cauchy model, with parameters showing high dependence on the thickness values.The refractive index at high frequency, as calculated using the Cauchy model, was observed to decrease with increasing film thickness, ranging from 1.87 at 106nm to 1.63 at 426nm. Similar values were obtained by fitting the optical refractive index data with the Wemple-DiDomenico relation. Additionally, the UV sensing performance of the films was evaluated against UV light of a single wavelength (365 nm) at applied voltages of 10, 20, and 30V. The rise and decay times were measured, with the film thickness of 426 nm exhibiting the shortest rise and decay times at a specific applied voltage.

Effect of Deposition Conditions on Properties of Aluminum Deposit Obtained from Aluminum Chloride-Acetamide Melts

Although aluminum (Al) electrodeposition using nonaqueous solutions has been widely studied, the process cost is not low. Because aluminum chloride (AlCl3)-acetamide (AcA) deep eutectic solvent (DES) takes low cost and produce better Al deposits than the AlCl3-based ionic liquid in dry air process costs may be reduced. However, the effect of the Al electrodeposition conditions using the AlCl3-AcA DES has not been clear. We investigated the effect of the operating temperature on the properties of Al electrodeposition using the AlCl3-AcA melt. At the operating temperate of 50 °C, the grain shape was fine-scale, similar to the surface morphology of the deposit in the AlCl3-urea melt.In contrast, at the operating temperature of 90 °C, the grain shape changed to fine grains. Based on these results, it was revealed that the grain shape and the preferential orientation of the Al deposit would be affected by operating temperature.

Influence of RE2O3 (Dy2O3, Yb2O3, and Lu2O3) buffer layers on the structural and ferroelectric characteristics of BiFeO3 thin films

This study investigates the impact of RE2O3 (Dy2O3, Yb2O3, and Lu2O3) buffer layers on the structural and ferroelectric properties of BiFeO3 thin films grown using a spin-coating method. BiFeO3 thin films with various RE2O3 buffer layers were analyzed using x-ray diffraction, atomic force microscopy, secondary ion mass spectrometry, and x-ray photoelectron spectroscopy to determine their crystalline structures, surface topographies, depth profiles, and chemical compositions, respectively. The RE2O3-buffered BiFeO3 film showed better electrical properties compared to the control BiFeO3 film. The buffer layer composed of Yb2O3 showed the lowest leakage current of 6.82 × 10−6 A cm−2, highest remnant polarization of 44.1 μC cm−2, and smallest coercive field of 189 kV cm−1 because of the incorporation of Yb3+ ions into the BiFeO3 film, high degree of (110) preferred orientation, high Fe3+ content, low surface roughness, reduction of Fe3+ valence fluctuation to Fe2+ ions, and decrease in oxygen vacancies. Such BiFeO3 thin films with various RE2O3 buffer layers using spin-coating method pave a pathway toward practical applications of spintronic, sensor and memory.

High-performance circularly polarized electroluminescence UV-OLED based on hot exciton molecules with preferred horizontal dipole orientation

Emitting circularly polarized electroluminescence (CPEL) directly endows the CP organic light-emitting diodes (CP-OLEDs) with great advantages in 3D display. But the highly efficient CP-OLEDs are still in great need, especially for devices emitting short-wavelength light such as ultraviolet (UV) CP-OLEDs. Herein, we report the first case of CP UV-OLED, fabricated by two pairs of enantiomers, (R)-/(S)-BNP-o-CzPI and (R)-/(S)-BNP-p-CzPI, established by chiral perturbation. Devices using 10 wt% enantiomers as dopants show UV CPEL at 396 nm with external quantum efficiency, Commission Internationale de l’Eclairage y value, and full width at half maxima of 7.2/6.9 %, 0.046/0.044 and 50/50 nm for (R)-/(S)-BNP-o-CzPI, respectively. The horizontal dipole orientations of the film with 10 wt% emitters in mCPCN are measured as high as 84.1/85.2 % and 88.1/88.7 % for (R)-/(S)-BNP-o-CzPI and (R)-/(S)-BNP-p-CzPI, respectively. Experiments and theoretical calculations indicate that the high EQEs are due to the high triplet exciton utility and large horizontal dipole orientation. In addition, the enantiomers show signigicant circularly polarized luminescence properties both in photoluminescence and in electroluminescence, and the device using (S)-BNP-o-CzPI has a large dissymmetry factors of 3.10 × 10−3 at emission maximum.

Fracture modeling in composite structures containing orthotropic materials by incorporating strain orthogonal decompositions into phase-field method of interfacial damage

PurposeThe phase-field method of interfacial damage is used to simulate the damage in composite structures containing the brittle orthotropic materials and their interface.Design/methodology/approachIn the brittle fracture modeling, the strain tensor is decomposed into positive and negative parts characterizing tension and compression behaviors. By requiring an elastic energy preserving transformation involving the elastic stiffness tensor, these two strain parts must satisfy the orthogonality condition in the sense that the elastic stiffness tensor responds as a metric. However, most of the recent phase-field methods for brittle fracture do not verify this orthogonality condition. Additionally, to describe the damage in structures with anisotropic phases, recent studies have used multiple phase-field variables, with each preferential orientation represented by a phase-field variable to describe the bulk damage of component materials. This approach increases the complexity of simulation procedure. These disadvantages motivate the present study aimed at enhancing the simulation method.FindingsThe present study improves the phase-field method of interfacial damage by (1) incorporating the strain orthogonality condition into the phase-field method; (2) using only one phase-field variable instead of multiple phase-field variables to simulate damage in component orthotropic phases; and (3) investigating the interaction between interfacial damage and bulk damage as well as the effect of orientation tensor of preferential orientation in each orthotropic phase and the interfacial parameters on crack branching in composite structures.Originality/valueThrough several simulation examples, the present simulation method is proven to be accurate, effective, and helps the simulation process simpler than previous relevant methods.

On the Origin of Enantioselectivity in Chiral Zeolite Asymmetric Catalyst GTM-3: Host-Guest Transfer of Chirality.

Knowledge of how extra-large-pore chiral zeolite asymmetric catalysts based on the -ITV framework imprint their chirality during a catalytic reaction is crucial in order to spread the scope for the catalytic enantioselective production of chiral compounds of interest. In this work, we have carried out a combined experimental and computational study on the catalytic activity of antipode GTM-3 catalysts during the ring-opening of trans-stilbene oxide with 1-butanol. Identification of the enantiomers of all the chiral species unraveled a surprising catalytic behavior: these chiral catalysts promote the transformation of one enantiomer of trans-stilbene oxide in the corresponding unlike product (with inversion of configuration of the attacked C) via an SN2 mechanism, and at the same time, the transformation of the other enantiomer of trans-stilbene oxide via an SN1-like mechanism into the like (with retention of configuration) and secondary products (diphenylacetaldehyde via Meinwald rearrangement and derived products). A computational study based on DFT + D methods suggested a potential explanation for this catalytic behavior, associated with a different orientation of trans-stilbene oxide enantiomers bound on the Ge(T7) positions in d4r units, which is stabilized by the development of intraframework H-bonds between the interrupted T7OH adjacent positions characteristic of this framework. Calculations suggest that each enantiomer of trans-stilbene oxide follows a different reaction pathway, one favoring the SN2 route by addition of butanol from the opposite side to form unlike-products, while the different orientation of the antipode enantiomer disfavors such SN2 route mainly by steric repulsions and at the same time favors the reaction toward the SN1 mechanism to give like- and secondary-products. Our study suggests that the strong enantioselectivity of GTM-3 catalysts for this reaction is associated with the particular orientation adopted by the chiral reactants within the chiral nanospace provided by the -ITV framework, similarly to what occurs with enzymes, and such preferential orientation is directly controlled by the asymmetric cavities where the reaction takes place, by the particular features of the Ge active sites in adjacent interrupted positions and by the presence of several framework OH groups in the nearby nanospace that interact with guest species. The experimental observations and the reaction mechanism proposed suggest that GTM-3 catalysts prepared from the (1S,2S) enantiomer of the N,N-ethyl-methyl-pseudoephedrinium organic agent should be enriched in the P4332 enantiomorphic space group of the -ITV framework and GTM-3 prepared from the (1R,2R) enantiomer in the antipode P4132. Interestingly, resolution of the absolute configuration of GTM-3 materials from 3D-electron diffraction data has been accomplished and confirms such an assignment, giving an average 82% enantio-enrichment in the corresponding chiral polymorph. Structure-solution of the location of the chiral structure-directing agents indicates that the transfer of chirality from the molecular component to the zeolite polymorph is governed by the development of strong H-bonds between the molecular hydroxyl group and the interrupted T(7)OH framework positions.

Enhanced gas sensing performance of ZnO and Pt-doped ZnO nanostructured films by chemical spray pyrolysis

This study focuses on the preparation and characterization of zinc oxide (ZO) and platinum-doped zinc oxide (Pt-ZO) nanostructured thin films using the chemical spray pyrolysis technique. Structural and morphological properties of the films were investigated via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). To understand the semiconducting nature and carrier dynamics, UV-Vis spectroscopy, electrical conductivity measurements, and a static gas sensing system were employed. The films exhibited crystallization in the hexagonal wurtzite structure with a preferred orientation along the (002) plane. FESEM images revealed the presence of small bright particles, particularly abundant in the 5 wt% Pt-doped ZO thin film, indicating the presence of platinum catalysts. Electrical conductivity measurements confirmed the semiconducting nature of the films. Optical parameters such as band gap and absorption index were obtained from UV-Vis spectroscopy. Gas sensing performance towards liquefied petroleum gas (LPG) showed that the 5 wt% Pt-doped ZO thin film exhibited a high response (69.9) to a 50 ppm concentration of LPG at 350 °C. The gas response and recovery times were observed to be 8 s and 12 s, respectively. These results are attributed to interactions between LPG molecules and adsorbed oxygen species on the sensor surface. Platinum atoms on the oxide surface facilitate the formation of oxygen vacancies and the dissociation of oxygen molecules at low temperatures, leading to increased adsorption and reaction with LPG molecules. This results in significant changes in the sensor's resistance, thereby amplifying the sensor response. The findings demonstrate the potential of Pt-doped ZO thin films for practical gas sensing applications.