- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Influence of lateral methyl and terminal substituents on the mesophase behaviour of four rings azo-ester liquid crystal compounds
摘要： The effect of introducing a lateral methyl substitution into the previously investigated laterally neat four-ring analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (Ina–e), on their mesophase behaviour was investigated for the newly prepared five homologous series of 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIna–e). Within each homologous series, the alkoxy group varies between 6, 8, 10, 12, 14, and 16 carbons, while the substituent, X, is a polar group that alternatively changes between the electron-donating (CH3O and CH3) groups, and the electron-withdrawing (Br and NO2) groups, including the unsubstituted homologues (IInc). Their mesophase stabilities were determined by DSC and phases identified by PLM. The results showed that independent of the alkoxy-chain length or the polarity of the substituent X, the nematic phase is predominant with relatively high stability and wide temperature ranges. All compounds show a good thermal stability in the mesophases domain, except the nitro and Br substituted derivatives bearing short alkoxy chain length. Comparison of the mesophase behaviour was also made between the present series and corresponding three-ring laterally CH3-substituted azo/ester analogues. UV-vis absorption spectra revealed that derivatives with electron donating or an electron withdrawing groups exhibited redshifts of the π→π* transition compared with unsubstituded derivative.
关键词： optical properties,polarisability anisotropy,mesophase stability,Four-ring azo/ester/azo derivatives,lateral-methyl substitution
更新于2025-09-23 15:22:29
-
The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass-ceramics
摘要： Calcium fluoro-aluminosilicate (4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO3 triangles and BO4 tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.
关键词： Mullite,Fluorapatite,Boron-Substitution,Calcium fluoro-aluminosilicate glasses
更新于2025-09-23 15:21:21
-
Effect of Magnesium Substitution on the Structural, Morphological, Optical and Wettability properties of Cobalt Ferrite Thin Films
摘要： Cobalt ferrite thin films with magnesium substitution (Co1-xMgxFe2O4 for 0.0 ≤ x ≤ 1.0) were grown on clean glass substrate with dimensions (75 mm × 25 mm × 1.45 mm) using spray pyrolysis method. The grown thin films were annealed at 500°C for 4 h and further used for structural, morphological, optical and surface wettability investigations. The structural characterizations of the prepared films were performed through X-ray diffraction (XRD) technique at room temperature. The analysis of the XRD pattern shows the formation of single phase cubic spinel structure of the films. The most intense peak (311) of the XRD pattern was used to estimate the average crystallite size. The obtained crystallite size varies between 16 nm to 19 nm confirming the nanocrystalline nature of the films. The lattice constant calculated from XRD data show decreasing nature from 8.386 ? to 8.365 ? with increase in magnesium content x. The variation of X-ray density with magnesium content x shows initial increasing nature and then decreasing nature. Metal cation active vibration modes, metal oxygen stretching and bending vibrations were confirmed through the Raman analysis. Surface morphology of the films was studied by using scanning and transmission electron microscopy (SEM and TEM) technique. Observations of SEM micrographs reveal that particles are in nanosize dimensions and almost distributed uniformly. Particle size calculated from TEM analysis was found to be in the range of 5-18 nm. The band gap of the films was measured by UV-VIS spectrophotometer. It is observed that, the energy band gap decrease from 2.83 eV to 2.37 eV as increase in magnesium substitution. The Photoluminescence study showed the characteristic near-band-edge emission of presently investigated films samples at around 710 nm. The contact angle measurements revealed the hydrophilic nature of all the thin films under investigation.
关键词： CoFe2O4,spray pyrolysis,SEM-TEM,thin films,Mg2+ substitution,PL
更新于2025-09-23 15:21:21
-
Pb <sub/>2</sub> GaF <sub/>2</sub> (SeO <sub/>3</sub> ) <sub/>2</sub> Cl: Band Engineering Strategy by Aliovalent Substitution for Enlarging Bandgap while Keeping Strong Second Harmonic Generation Response
摘要： Wide bandgap and strong second-order generation (SHG) effect are two crucial but contradictory conditions for practical nonlinear optical (NLO) materials. Herein, a new NLO crystal Pb2GaF2(SeO3)2Cl (I) containing novel functional (GaO3F3)6? octahedra is designed and synthesized by a rational band engineering strategy with aliovalent substitution. Benefiting from the removal of transition metal cations and the introduction of bridged F anions, I exhibits the widest bandgap among all reported phase-matchable NLO selenites. Meanwhile, a strong SHG response more than 4.5 times of KH2PO4 (KDP) is maintained. The dominate role of the (GaO3F3)6? groups to the enlarged bandgap in I are elucidated by first-principles studies.
关键词： aliovalent substitution,second harmonic generation,nonlinear optical materials,selenites,band engineering
更新于2025-09-23 15:21:21
-
A new diffusion and substitution based cryptosystem for securing medical image applications
摘要： Due to the rising privilege for tele-health facilities have sophisticated responsiveness in the usage of medicinal image safeguard proficiency. It mainly compact with patient records that are secretive and must only available to legal person. So the medical image safety becomes a very significant problem, when patient evidence is conveyed through the public network. In this paper, a secret key of 128-bits size is generated by an image histogram. Initially, the photo sensitive feature of digital imaging and communications in medicine image is decomposed by the mixing process. The resulting image is distributed in key reliant blocks and further, these blocks are passed through key reliant diffusion and substitution processes. A total of five rounds are used in the encryption method. Finally the generated secret key is embedded within the encrypted image in the process of steganography. This also enhances the security of proposed cipher. At the receiver side the secret key was recovered from the embedded image and decryption operation was performed in inverse format. Performance analysis designates that the proposed cipher is more secure.
关键词： substitution,steganography,encryption,diffusion,histogram
更新于2025-09-23 15:21:21
-
An Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1-xCdxSnS4 Heterointerface for Photovoltaic Applications
摘要： To improve the constraints of kesterite Cu2ZnSnS4 (CZTS) solar cell, such as undesirable band alignment at p?n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu2Zn1-xCdxSnS4 through cost-effective solution-based method without post-annealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu2Zn1-xCdxSnS4 materials. Tunable direct band gap energy ranging from 1.51 eV to 1.03 eV with high absorption coefficient was demonstrated for the Cu2Zn1-xCdxSnS4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu2Zn1-xCdxSnS4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation photo-excited charge carriers in Cu2CdSnS4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point towards efficient separation of photoexcited carriers across the p?n junction in the ultrafast time scale and highlight a route to improve device performances.
关键词： grain boundary,photovoltaic,cation substitution,Earth-abundant material,interfacial engineering,band offset,ultrafast carrier dynamics
更新于2025-09-23 15:21:01
-
Magneto-optical properties of Rare Earth metals substituted Co-Zn spinel nanoferrites
摘要： Cobalt–zinc ferrite nanoparticles (NPs) substituted with three different metals, Co0.5Zn0.5RexFe2-xO4 (RE = Ce, Dy, and Y; 0.00 ≤ x ≤ 0.05) were prepared hydrothermally. Fourier Transform-Infrared (FT-IR) Spectroscopy, X-ray powder diffraction (XRD), Field-Emission Scanning Electron Microscope (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) and Vibrating Sample Magnetometry (VSM) analyzed the products. The formation of cubic phase of spinel Co-Zn ferrite NPs were confirmed through XRD, FT-IR and FE-SEM techniques. The structural investigation of NPs by XRD revealed that the lattice parameter "a" decreases with the introduction of the RE in the ferrite structure by the substitution of Fe3+ by RE ions. The different magnetic parameters of Co0.5Zn0.5RexFe2-xO4 (RE = Ce, Dy, and Y; 0.00 ≤ x ≤ 0.05) NPs such as the saturation magnetization, coercivity, remanence, and magnetic moment were calculated and discussed in relation to structure and microstructure properties. M (H) hysteresis curves indicated that the samples exhibit superparamagnetic nature at room temperature. A slight improvement in the magnetization was obtained especially for the Ce- and Y-substituted Co0.5Zn0.5Fe2O4 (CZF) NPs at a certain RE level. However, the case Dy-substituted CZF products showed a sharp decrease in the magnetization with x > 0.01. The results are mostly ascribed to the substitution of smaller Fe3+ ions with larger RE3+ ions.
关键词： Spinel ferrites,Morphology,Rare earth substitution,Hydrothermal,Magnetic properties
更新于2025-09-23 15:21:01
-
The effect of Yb3+ ion substitution on dielectric and microstructural properties of Y3Al5O12 ceramics
摘要： The electrical and dielectric properties of Y3Al5O12 (yttrium aluminum garnet, YAG) ceramics are investigated in detail. YAG:(Yb)x (0.01 ≤ x ≤ 0.09) was synthesized by a solid state reaction and characterized by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The electrical and dielectric properties have been intensively studied under certain bias voltages up to a frequency of 10 MHz. These properties are dependent on the substitution rates, independent of the bias voltages. The experimental result shows that Yb3+ ion substitution into YAG ceramics significantly influences the conductivity, dielectric constant, and lossy mechanisms, which is probably owing to the 3d-Al ions and 4f-Yb ions incorporated at different positions of structural symmetries in Y3?xYbxAl5O12 (0.00 ≤ x ≤ 0.09) ceramics.
关键词： ceramics,Yb3+ ion substitution,Y3Al5O12,dielectric properties,microstructural properties
更新于2025-09-23 15:21:01
-
PRESERVATIVE TREATMENT OF FENCE POSTS EVALUATION THROUGH PHOTOCOLORIMETRY SEGMENTATION PERFORMANCE
摘要： The research object was evaluating the quality of preserving treatment of Eucalyptus sp. fence posts by the sap substitution method and comparing the penetration through the traditional and photocolorimetry segmentation methods. The fence posts, 2,0 meters long and with a diameter between 8 and 12 cm, were exposed to 2, 3 and 4% concentrations of CCB based-product active ingredients for 10 days. The penetrations were analyzed using two methodologies, one by the Image Pro Plus 4.5 software, using photocolorimetry segmentation method performance, and by analyzing the product retention in four positions of the treated fence posts. The treatment submitted pieces attained low penetration and, thus, the retention values were less than the required for direct contact with the ground. On the other hand, the proposed photocolorimetry segmentation methodology was efficient and could be an alternative to determine a more precise and fast penetration.
关键词： Eucalyptus,Sap substitution,Penetration
更新于2025-09-23 15:21:01
-
Locating Cytosine Conical Intersections by Laser Experiments and <i>Ab Initio</i> Calculations
摘要： The decay mechanism of S1 excited cytosine (Cyt) and the effect of substitution are studied combining jet-cooled spectroscopy (nanosecond resonant two-photon ionization (R2PI) and picosecond lifetime measurements) with CASPT2//CASSCF computations for eight derivatives. For Cyt and five derivatives substituted at N1, C5, and C6, rapid internal conversion sets in at 250?1200 cm?1 above the 000 bands. The break-off in the spectra correlates with the calculated barriers toward the "C5?C6 twist" conical intersection, which unambiguously establishes the decay mechanism at low S1 state vibrational energies. The barriers increase with substituents that stabilize the charge shifts at C4, C5, and C6 following (1ππ*) excitation. The R2PI spectra of the clamped derivatives 5,6-trimethyleneCyt (TMCyt) and 1-methyl-TMCyt (1M-TMCyt), which decay along an N3 out-of-plane coordinate, extend up to +3500 and +4500 cm?1.
关键词： CASPT2//CASSCF computations,jet-cooled spectroscopy,internal conversion,substitution effect,R2PI spectra,decay mechanism,cytosine,conical intersection
更新于2025-09-23 15:19:57