stoichiometric composition
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2022 ◽  
Abideen Adejuwon Ibiyemi ◽  
Yusuf taofeek Gbadebo ◽  
Olusayo Olubosede ◽  
Akinrinola Olusola ◽  
Hamzat Adebayo Akande

Abstract Cadmium nickel (Cd-Ni) ferrite samples have been successfully synthesized via chemical co-precipitation technique. The structural analysis revealed the formation of FCC framework and Fe-phase in a trivalent state. The crystallite size is decreased with increasing Cd2+ ion composition whereas the lattice constant is increased. SEM was used to obtain the surface morphology and average grain size of the microstructure. The FTIR shows the formation of metal oxide, hydroxyl and carboxylic groups. EDX revealed the formation of Ni2+, Cd2+, Fe3+, and O2- ions in proper stoichiometric composition. Large optical losses were revealed by Cd2+ poor-NiFe2O4 samples whereas Cd2+ rich-CdxNi1-xFe2O4 samples revealed low optical losses and showed enhanced photoconductivity and photoelectric effect. Result from optical analysis showed that Cd2+ rich-CdxNi1-xFe2O4 nanoparticles can be used as infrared (IR) detector, ultraviolet (UV) filter and in optoelectronics device applications. VSM measurement showed an increase in saturation magnetization and decrease in coercivity as Cd2+ ion content is increased. The remanance magnetization and magnetic anisotropy were also examined. Photoluminescence (PL) spectroscopy examined the nature of the light emission of the samples at the excitation wavelength 380 nm and emission of series of colours such as red, green, yellow, orange and violet light at different wavelengths were found.

2022 ◽  
Vol 13 ◽  
Chengji Piao ◽  
Stephan J. Sigrist

The so-called active zones at pre-synaptic terminals are the ultimate filtering devices, which couple between action potential frequency and shape, and the information transferred to the post-synaptic neurons, finally tuning behaviors. Within active zones, the release of the synaptic vesicle operates from specialized “release sites.” The (M)Unc13 class of proteins is meant to define release sites topologically and biochemically, and diversity between Unc13-type release factor isoforms is suspected to steer diversity at active zones. The two major Unc13-type isoforms, namely, Unc13A and Unc13B, have recently been described from the molecular to the behavioral level, exploiting Drosophila being uniquely suited to causally link between these levels. The exact nanoscale distribution of voltage-gated Ca2+ channels relative to release sites (“coupling”) at pre-synaptic active zones fundamentally steers the release of the synaptic vesicle. Unc13A and B were found to be either tightly or loosely coupled across Drosophila synapses. In this review, we reported recent findings on diverse aspects of Drosophila Unc13A and B, importantly, their nano-topological distribution at active zones and their roles in release site generation, active zone assembly, and pre-synaptic homeostatic plasticity. We compared their stoichiometric composition at different synapse types, reviewing the correlation between nanoscale distribution of these two isoforms and release physiology and, finally, discuss how isoform-specific release components might drive the functional heterogeneity of synapses and encode discrete behavior.

2021 ◽  
Vol 12 (4) ◽  
pp. 469-481
Muhammad Jamaluddin Ahmed ◽  
Muhammad Jihan Uddin ◽  
Muhammad Emdadul Hoque

A new spectrophotometric reagent, salicylaldehyde-orthoaminophenol (Sal-OAP) has been synthesized and characterized for the determination of selenium through novel reaction techniques. Also, a new highly selective, and sensitive spectrophotometric method for the nano-trace determination of selenium using salicylaldehyde-orthoaminophenol (Sal-OAP) has been developed. Sal-OAP undergoes reaction in a slightly acidic solution (0.0001-0.0002 M H2S04) with selenium (IV) to give an orange-red chelate, which has an absorption maximum at 379 nm. The reaction is instantaneous and absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 6.4×105 L/ and 1.0 ng/cm2 of, respectively. Linear calibration graphs were obtained for 0.001-40.000 mg/Lof Se having detection limit of 0.1 µg/L and RSD 0-2 %. The stoichiometric composition of the chelate is 1:2 (Se:Sal-OAP). A large excess of over 60 cations, anions and some common complexing agents, such as chloride, azide, tartrate, EDTA, SCN¯etc., do not interfere in the determination. The developed method was successfully used in the determination of selenium in several Certified Reference Materials (Alloys, steels, human urine, bovine liver, drinking water, tea, milk, soil, and sediments) as well as in some environmental waters (Potable and polluted), biological fluids (Human blood, urine, hair, and milk), soil samples, food samples (Vegetables, rice, and wheat) and pharmaceutical samples (Tablet and syrup) and solutions containing both selenium (IV) and selenium (VI) as well as complex synthetic mixtures. The results of the proposed method for assessing biological, food and vegetables and soil samples were comparable with ICP-OES and AAS were found to be in excellent agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

2021 ◽  
Vol 104 (4) ◽  
pp. 138-148
A.M. Kozhanova ◽  
B.S. Temirgaziyev ◽  
A. Zhanarbek ◽  
B.I. Tuleuov ◽  

The article presents materials on the isolation of ecdysterone substance from medicinal plant raw materials Silene wolgensis (Hornem.) Bess. ex. Spreng (Volga smolyovka). For the first time, the optimization of the method for ecdysterone substance obtaining from the aboveground part of the superconcentrator of phytoecdysteroids of the Silene wolgensis was carried out and based on it a pilot industrial regulation for the isolation of ecdysterone and an encapsulated water-soluble form were developed. It was found, that the interaction of the substrate molecule and the clathrate forms a substance that can dissolve in water and other more polar solvents, thereby solving the problem of bioavailability of the main hydrophobic drug. The method developed for producing the substance ecdysterone and its water-soluble encapsulated with β-cyclodextrin form was implemented into production at the Karaganda pharmaceutical plant. NMR studies of changes in the chemical shifts of protons of substrates and receptors illustrated that ecdysterone interacts with β-cyclodextrin to form supramolecular inclusion complexes with stoichiometric composition of 1:1

Рустам Мухамедович Калмыков ◽  
Ахмед Мацевич Кармоков ◽  
Замир Валериевич Шомахов ◽  
Аминат Хусеновна Дышекова

В работе проведены электронно-микроскопические исследования полупроводниковых соединений на основе PbTe с примесями дисперсных фаз CdSe. Как показали результаты исследования, в исходном нелегированном соединении PbTe содержание атомов свинца составляет около 63,8 вес%, а содержание теллура составляет 36,2 вес%, т.е. соответствует стехиометрическому составу. Согласно изображениям электронного микроскопа, эти компоненты равномерно распределены по площади. Результаты исследования также показали, что образующиеся новые фазы имеют размеры зерен от 90 нм до 2 мкм. Полученные значения параметра решетки для соединения теллурида свинца и сингония хорошо согласуются с литературными данными. Структура образующихся фаз имеет такую же симметрию, как и исходное нелегированное соединение PbTe, гранецентрированную кубическую решетку с классом симметрии Fm3m. В молекулах новых образующихся фаз, в которых преобладают содержания элементов Cd и Se, обнаружено изменение сингонии кристаллической решетки. In this work, electron microscopic studies of semiconductor compounds based on PbTe with impurities of dispersed CdSe phases have been carried out. As shown by the research results, in the initial undoped PbTe compound, the content of lead atoms is about 63,8 wt.%, and the tellurium content was 36,2 wt.%, i.e. corresponded to the stoichiometric composition. According to the electron microscope images, these components are evenly distributed over the area. The results of the study also showed that the formed new phases had grain sizes from 90 nm to 2 pm. The obtained values of the lattice parameter for the lead telluride compound and crystal system are in good agreement with the literature data. The structure of the resulting phases has the same symmetry as the initial undoped PbTe compound, a face-centered cubic lattice with the Fm3m symmetry class. In the molecules of the newly formed phases, in which the abundances of the elements Cd and Se prevailed, a change in the crystal lattice syngony was found.

Николай Васильевич Сидоров ◽  
Наталья Александровна Теплякова ◽  
Михаил Николаевич Палатников

Методом ИК-спектроскопии в области валентных колебаний OH - групп выполнен анализ комплексных дефектов, обусловленных наличием в структуре кристалла водородных связей, в номинально чистых кристаллах ниобата лития конгруэнтного и стехиометрического состава с разным отношением Li / Nb, а также в кристаллах LiNbO: Zn(0,04 - 6,5 мол.% ZnO), легированных цинком в широком диапазоне концентраций, полученным по технологии прямого легирования расплава. Выявлено влияние легирующих примесей на концентрацию OH - групп, вид и локализацию комплексных дефектов в структуре кристалла. Показано, что изменение количества позиций атомов водорода в структуре кристалла LiNbO позволяет с достаточной точностью судить о соответствии его состава стехиометрическому или конгруэнтному составу. Для легированных кристаллов LiNbO : Zn(0,04 - 6,5 мол.% ZnO) получены данные, свидетельствующие об изменении при прохождении концентрационных порогов характера комплексообразования OH - групп с точечными дефектами катионной подрешетки. При этом, вследствие изменения механизма вхождения легирующего катиона в структуру кардинально изменяются свойства кристалла. Вклад в различие частот (и, соответственно, в значение квазиупругих постоянных связей OH -) в спектре конгруэнтного кристалла и легированных кристаллов может вносить также различие электроотрицательностей и ионных радиусов основных и легирующих катионов. An analysis of complex defects was carried out by IR-spectroscopy method in the area of OH - groups stretching vibrations. The defects are caused by hydrogen bonds present in the structure of nominally pure congruent lithium niobate crystals, crystals of stoichiometric composition with a different Li / Nb ratio, as well as in LiNbO: Zn(0,04 - 6,5 мол.% ZnO) crystals doped in a wide range of concentrations due to direct doping of the melt method. Dopants were determined to influence OH - groups concentration, type and localization of complex defects in the crystals structure. A change in the amount of hydrogen sites in the LiNbO crystals structure was shown to evaluate the composition either stoichiometric or congruent. The character of OH - groups complexing with cation sublattice point defects was shown to change when doped crystals LiNbO: Zn(0,04 - 6,5 мол.% ZnO) trespass concentration thresholds. Dopant incorporation mechanism changes at this drastically, thus crystal properties also change quite sharply. Frequencies (as well as quasi-elastic constants of OH - bonds) change in congruent and doped crystals due to a difference in electronegativities and ionic radii of the main and dopant cations.

V. A. Babkin ◽  
D. S. Andreev ◽  
A. V. Ignatov ◽  
E. S. Titova ◽  
V. T. Fomichev ◽  

The ab initio 3.21G method was used to study the initiation mechanism of 2-methylpentene-1 under the action of a complex catalyst AlClCH - HO in heptane of stoichiometric composition 1:1:1:1. The energetics of this reaction is estimated, the values of its energy barrier and enthalpy are obtained.

2021 ◽  
Vol 4 (1) ◽  
pp. 43-48
I Gusti Agung Putra Adnyana ◽  
I Ketut Sukarasa ◽  
Komang Ngurah Suarbawa

The development of permanent magnet-based rare earth metals becomes a serious problem if the raw materials are difficult to find. The solution chosen is to utilize an oxide-based permanent magnet with little substitution of rare earth metals. In this study presented a permanent magnetic synthesis of barium hexaferrite-based oxides that were doped with La and Ce atoms. The synthesis of this material uses the wet mechanical milling technique to obtain the single phase permanent magnet system Ba1-x-yLaxCeyFe12O19 (x = 0, 0.02, 0.04 and y = 0. 0.05, 0.1). The precursor is weighed according to stoichiometric composition and is milled for 5 hours then compressed at a pressure of 7000 Psi. Sintering temperature for the formation of the barium hexaferrite phase at 1200oC for 2 hours. All samples after sintering were characterized using XRD and EDS.  A single phase is obtained on all sample compositions with a hexagonal P63/mmc structure and is supported by elemental analysis data that each substituted sample contains elements La and Ce. Lattice parameters a, b, and c appear to decrease with increasing concentrations of La and Ce doping ions with a ratio of c/a in the range of 3.93-3.94.

Islam M El radaf ◽  
Hnan Y Alzahrani

Abstract We deposited CuGaSnS4 thin films on soda-lima glass substrates via a spray pyrolysis process. The X-ray diffraction of CuGaSnS4 films established the formation of an orthorhombic single phase. In addition, the structural parameters of the CuGaSnS4 films were estimated by Debye-Scherer’s formulas, which showed that an enhancement in crystallite size (D) values occurred by increasing the thickness of the investigated films. The EDAX pattern of CuGaSnS4 films confirms a stoichiometric composition. The optical results revealed that the CuGaSnS4 films possessed a direct optical energy gap (Eg). The Eg values were reduced from 1.50 to 1.38 eV with the increase in thickness. Also, there was an observed increase in the linear refractive index and the linear absorption coefficient values occurred due to the increased thickness. Finally, the optoelectrical constants of the sprayed CuGaSnS4 films such as the optical conductivity (σopt) and the optical free carrier concentration to effective mass (N_opt/m^* ) were enlarged with increasing film thickness. The nonlinear optical study showed that the increase in film thickness enhanced the nonlinear optical constants of CuGaSnS4 films. The hot-probe procedure shows that the sprayed CuGaSnS4 films expose p-type conductivity.

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