Se Sample Research Articles

Effect of Na doping on structural, optical, and dielectric properties of SnSe polycrystals

Recently, tin selenide has attracted vast research interest in many fields due to its unique properties. Here, Na-doped SnSe polycrystals were successfully synthesized using hydrothermal method. Single phase was exhibited by all the samples as revealed from X-ray diffraction (XRD). Scanning electron microscope (SEM) studies for undoped SnSe showed a 2D plate-like morphology and converted it into 3D flower-like morphology with increasing Na concentration. The optical bandgap values obtained using UV–VIS–NIR diffuse reflectance spectroscopy were found to decrease with increasing Na concentration. Dielectric and electrical modulus studies were carried out in the frequency range from 100 Hz to 10 MHz for temperatures from 323 to 523 K. Correlated barrier hopping (CBH) is a probable mechanism for the charge carriers in all the compositions of NaxSn1−xSe. The electrical modulus studies indicated an incomplete dielectric relaxation of the non-Debye type. The high values of the real part of permittivity and AC conductivity for the Na0.20Sn0.80Se sample have potential applications as capacitive energy-storage devices.

Structure and thermoelectric properties of nickel-doped copper selenide synthesised in a hydrogen atmosphere

Nickel-doped copper selenide—Cu2-xNixSe (x = 0; 0.01; 0.02; 0.03)—materials with high thermoelectric properties were synthesised through reduction of reagents in hydrogen. The impact of the nickel content on both the microstructure and thermoelectric properties was examined. The nickel-doped samples’ microstructure differed significantly from pristine copper selenide. Besides Cu2Se, copper precipitations were present in the materials. The presence of the metallic nanoparticles in the nickel-doped materials enhanced the electrical conductivity without significantly changing the Seebeck coefficient. Above 500 K, the structure of the doped samples also resulted in decreased thermal conductivity. Also, the impact of the Cu2Se phase transition on thermoelectric properties is visible. The highest ZT value, equal to 0.8 at 650 K, was reached for the Cu1.98Ni0.02Se sample.

Composition Tuning of Nanostructured Binary Copper Selenides through Rapid Chemical Synthesis and their Thermoelectric Property Evaluation.

Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric (TE) Cu2−xSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding Cu1.8Se at 200 °C and Cu2Se at 250 °C within 6–8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure Cu1.8Se exhibited highly compacted and oriented grains that were similar in size in comparison to Cu2Se, which led to its high electrical and low thermal conductivity, reaching a very high power-factor (24 µW/K−2cm−1). Density-of-states (DOS) calculations confirm the observed trends in electronic properties of the material, where Cu-deficient phase exhibits metallic character. The TE figure of merit (ZT) was estimated for the materials, demonstrating an unprecedentedly high ZT at 875 K of 2.1 for Cu1.8Se sample, followed by 1.9 for Cu2Se. Synthetic and processing methods presented in this work enable large-scale production of TE materials and components for niche applications.

High Thermoelectric Performance of Co-Doped P-Type Polycrystalline SnSe via Optimizing Electrical Transport Properties.

This work systematically investigated the thermoelectric properties of p-type Na and M (M = K, Li, Ag) codoped polycrystalline SnSe. It is found that the electrical properties of polycrystalline SnSe can be improved significantly for (Na, Ag) codoped samples, contributed by the enhanced carrier concentration. Specifically, a carrier concentration of 6.23 × 1019 cm-3 was obtained in Sn0.98Na0.016Ag0.004Se sample at 335 K, an increase of 18% compared with that of the Na single-doped sample (5.22 × 1019 cm-3). The power factor reached ∼0.73 mW m-1 K-2 for the Sn0.98Na0.016Ag0.004Se sample at 785 K, enhanced by ∼26% compared with Na single-doped one. In addition, Sn-rich and Ag-rich particles/areas observed in the matrix of Sn0.98Na0.016Ag0.004Se contribute to the reduction of lattice thermal conductivity from 0.61 W m-1 K-1 for Sn0.98Ag0.02Se to 0.47 W m-1 K-1 at 785 K. The combination of simultaneously enhanced power factor and depressed thermal conductivity leads to a maximum ZT ≈ 1.2 at 785 K and a high average ZT ≈ 0.74 at 335-785 K for Sn0.98Na0.016Ag0.004Se, and generating a high theoretical conversion efficiency of ∼11%. These illuminating discoveries could provide routes to enhance the thermoelectric performance in p-type polycrystalline SnSe.

Contrasting roles of small metallic elements M (M = Cu, Zn, Ni) in enhancing the thermoelectric performance of n-type PbM0.01Se

The carrier concentration of PbCu0.01Se sample increases suddenly, which results from the release of 3d orbital electrons in Cu+ ions.

Chemical Constituents of Zarrouk Medium Affect Growth, Pigments and Metabolites Productions of Spirulina platensis

GROWTH (OD, Dw), pigments (Chl. a, carotenoids) and metabolites (proteins, carbohydrates, phenolic, flavonoids) have been evaluated under different component concentrations of Zarrouk media (NaCl, NaNO3, K2HPO4 and K2SO4) as well as some heavy metals (Zn, Cu, Se). The normal concentration of the tested components in Zarrouk medium (control) was found to induce the maximum growth parameters, pigments and metabolites contents. Acetone extracts of the normal concentrations (1.0g/L NaCl, 2.5g/L NaNO3, 0.5g/L K2HPO4 and 1g/L K2SO4) revealed the highest phenolic contents. While the ethanolic extracts of starved media (0.0g/L) of N or S, P (0.2g/L) as well as high salinity (4g/L) showed the greatest flavonoid production. Concerning heavy metals, Zn enhanced all the investigated parameters more than those performed by Cu, Se and control sample. In absence of all heavy metals, both acetone and ethanolic extracts revealed the greatest phenolic and flavonoids contents.

High thermoelectric performance and low thermal conductivity in Cu2-xNaxSe bulk materials with micro-pores

Cu2Se has been considered as a promising thermoelectric material due to its unique structure and excellent performance. Herein, a series of Cu2-xNaxSe (x = 0, 0.01, 0.02, 0.03, and 0.04) polycrystalline samples were synthesized by combining hydrothermal synthesis and hot pressing to investigate the effects of Na-doping on the microstructure and thermoelectric properties of Cu2Se. Compared with the pristine Cu2Se, the Na-doping introduces numerous micro-pores that can optimize the thermal transport performance by strong phonon scattering effects of interfaces between the micro-pores and grains. The doped samples have excellent electrical properties and low thermal conductivity. The maximum value of ZT = 2.1 is obtained at 973 K for the Cu1.96Na0.04Se sample with nominal composition. The results confirm that introducing Na into Cu2Se is an effective and convenient strategy to improve the thermoelectric performance of the Cu2Se alloy by decreasing the lattice thermal conductivity.

High thermoelectric performance and low thermal conductivity in K-doped SnSe polycrystalline compounds

SnSe single crystal showed a high thermoelectric zT of 2.6 at 923 K mainly due to an extremely low thermal conductivity 0.23 W m−1 K−1. It has anisotropic crystal structure resulting in deterioration of thermoelectric performance in polycrystalline SnSe, providing a low zT of 0.6 and 0.8 for Ag and Na-doped SnSe, respectively. Here, we presented the thermoelectric properties on the K-doped KxSn1−xSe (x = 0, 0.1, 0.3, 0.5, 1.5, and 2.0%) polycrystals, synthesized by a high-temperature melting and hot-press sintering with annealing process. The K-doping in SnSe efficiently enhances the hole carrier concentration without significant degradation of carrier mobility. We find that there exist widespread Se-rich precipitates, inducing strong phonon scattering and thus resulting in a very low thermal conductivity. Due to low thermal conductivity and moderate power factor, the K0.001Sn0.999Se sample shows an exceptionally high zT of 1.11 at 823 K which is significantly enhanced value in polycrystalline compounds.

Realizing High Thermoelectric Performance below Phase Transition Temperature in Polycrystalline SnSe via Lattice Anharmonicity Strengthening and Strain Engineering.

We report the high thermoelectric performance of p-type polycrystalline SnSe obtained below the phase transition temperature by harnessing Pb doping and introducing Sn vacancies. The enhanced carrier concentration induced by Pb doping and introducing Sn vacancies contributes to enhancements of electrical conductivity and power factor of polycrystalline SnSe. We demonstrate that the lattice anharmonicity is strengthened by Pb substitution and Sn vacancies through forming weaker bonds. We find that Pb substitution introduces huge stress field in the interior of the SnSe grains. The thermal conductivity can be greatly reduced by lattice anharmonicity strengthening and applying huge stress field. The lattice thermal conductivity is reduced to as low as 0.18 W m-1 K-1 in the Sn0.92Pb0.03Se sample at 773 K. As a result, a remarkable high ZT of ∼1.4 was achieved at 773 K in the Sn0.93Pb0.02Se sample through lattice anharmonicity strengthening and strain engineering.

Hydrothermal Venting at Hinepuia Submarine Volcano, Kermadec Arc: Understanding Magmatic‐Hydrothermal Fluid Chemistry

AbstractThe Hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast, with an active cone complex in the SE. Hinepuia is one of several active volcanoes in the northern segment of the Kermadec arc. Regional magnetic data show no evidence for large‐scale hydrothermal alteration at Hinepuia, yet plume data confirm present‐day hydrothermal discharge, suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal. Gravity data are consistent with crustal thinning and shallow mantle under the volcanic center. Following the discovery of hydrothermal plumes over Hinepuia, the submersible Shinkai 6500 was used to explore the SE cone and sample hydrothermal fluids. The chemistry of hydrothermal fluids from submarine arc and backarc volcanoes is typically dominated by water‐rock interactions and/or magmatic degassing. Chemical analyses of vent fluids show that Hinepuia does not quite fit either traditional model. Moreover, the Hinepuia samples fall between those typically ascribed to both end‐member fluid types when plotted on a K‐Mg‐SO4 ternary diagram. Due to evidence of strong degassing, abundant native sulfur deposition, and H2S presence, the vent sampled at Hinepuia is ultimately classified as a magmatic‐hydrothermal system with a water‐rock influence. This vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation. Magmatic‐hydrothermal fluid chemistry appears to be controlled by a combination of gas flux, phase separation processes, and volcano evolution and/or distance from the magma source.

English

The aerial parts of Achillea fragrantissima (Forssk.) Sch. Bip., wildly grown in Egypt, yielded 0.8 and 1.5% (v/w) of essential oils prepared by hydrodistillation (HD), or by conventional volatile solvent extraction method (preparation of the “absolute”, SE), respectively.  The volatile components of this essential oil were determined by GC–MS analyses. Twenty eight compounds were identified in the HD sample, among which caryophyllene oxide (23.50%), 1-terpinen-4-Ol (11.15%), viridiflorol and guaienol (9.84%) were the main components. Meanwhile, 21 compounds were detected in the SE sample; 1-terpinen-4-Ol (30.90%), p-cymen-3-Ol (21.22%) were the main components. The anticancer activity of the prepared oils was evaluated against human breast cancer cell line (MCF-7) and colon cancer cell line (HCT116). The oil prepared by hydrodistillation revealed an IC50 0.51 µg/ml for MCF-7 and 0.62 µg /ml for HCT116, while that prepared by volatile solvent extraction had a value of 0.80 µg/ml for MCF-7 and 0.91 µg /ml for HCT116. Key words: Achillea fragrantissima, cytotoxic and terpinen-4-ol.

Improved thermoelectric performance in p-type Bi0.48Sb1.52Te3 bulk material by adding MnSb2Se4**Project supported by the National Natural Science Foundation of China (Grant Nos. 51472052 and Y6J1421A41).

Bismuth telluride (BiTe based alloys, such as p-type Bi Sb Te , have been leading candidates for near room temperature thermoelectric applications. In this study, Bi Sb Te bulk materials with MnSb Se were prepared using high-energy ball milling and spark plasma sintering (SPS) process. The addition of MnSb Se to Bi Sb Te increased the hole concentration while slightly decreasing the Seebeck coefficient, thus optimising the electrical transport properties of the bulk material. In addition, the second phases of MnSb Se and Bi Sb Te were observed in the Bi Sb Te matrix. The nanoparticles in the semi-coherent second phase of MnSb Se behaved as scattering centres for phonons, yielding a reduction in the lattice thermal conductivity. Substantial enhancement of the figure of merit, ZT, has been achieved for Bi Sb Te by adding an Mn Cu Sb Se (2 mol%) sample, for a wide range of temperatures, with a peak value of 1.43 at 375 K, corresponding to improvement over its Bi Sb Te counterpart. Such enhancement of the thermoelectric (TE) performance of p-type Bi Te based materials is believed to be advantageous for practical applications.

Термоэлектрические и тепловые свойства суперионных сплавов AgxCu2−xSe (x = 0.01, 0.02, 0.03, 0.04, 0.25)

The results of investigations of the thermoelectric and thermal properties of AgxCu2-xSe (x = 0.01, 0.02, 0.03, 0.04, 0.25) alloys are presented in the paper. The AgxCu2-xSe samples with low silver content were prepared by solid state reaction of the pure elements in argon atmosphere at 773 K temperature. The Ag0.25Cu1.75Se sample was sintered by solid phase reaction of Cu2Se and Ag2Se mixture in argon atmosphere at 673 K. At room temperature X-ray diffraction study revealed the presence of three phases in the samples: the Cu2Se orthorhombic phase, the Cu1.8Se cubic phase and the AgCuSe orthorhombic phase. The heat of the superionic phase transition in Ag0.01Cu1.99Se was measured equal to (3.5 ± 0.3) kJ / mol. For Ag0.25Cu1.75Se sample the heat of the superionic phase transition was found to be (3.1 ± 0.3) kJ / mol. In addition to intense peak of the superionic phase transition occupying the 373-423 K temperature range, the weak thermal effects for Ag0.01Cu1.99Se at 317 K, and ones for Ag0.25Cu1.75Se at 316 K and 437 K were observed too. In the investigated temperature range of 290 - 770 K the electronic conductivity σ decreases, and Zeebeck coefficient α increases with silver content in the compounds. The thermal conductivity of Ag0.03Cu1.97Se compound decreases monotonically from 0.54 to 0.34 W m-1 K-1 in the range 420 - 650 K after the superionic phase transition, resulting in thermoelectric efficiency ZT = σα2T/λ increases monotonically, reaching a value ZT = 1 at 650 K.

Microstructures and thermoelectric transports in PbSe-MnSe nano-composites

Thermoelectric materials can generate electricity by harnessing the temperature gradient and lowering the temperature through applying electromotive force. Lead chalcogenides based materials, especially PbTe-based ones, have shown extremely high thermoelectric performance. PbSe has a similar crystal structure and band structure to PbTe. Compared with the commonly-used PbTe, PbSe possesses a high melting point and has an abundant reserve of Se, making it attractive to high temperature thermoelectric applications. It has been theoretically proposed that Mn-doping in lead chalcogenide should be able to lower the temperature of band degeneracy, and experimental evidences have been represented in Mn-PbTe. However, such an experimental study as well as the investigations of influences of Mn on microstructure, mechanical, electrical and thermal properties has not been conducted in Mn-PbSe. In this work, Pb0.98-xMnxNa0.02Se (0 x 0.12) materials are prepared by the melting-quenching techniques combined with rapid hot-press sintering. Effects of Mn doping on the microstructures, mechanical and thermoelectric properties of PbSe samples are systematically studied. The refined lattice parameters from X-ray powder diffraction patterns show that the solubility of Mn in the matrix is in a range from 0 to 0.04. The back-scattered electron images and elemental maps reveal that the MnSe-rich impurity phases exist in the PbSe matrix, which makes the PbSe-MnSe system a nano-composite system. Pb0.96Mn0.02Na0.02Se has also such microstructures, implying that the solubility of Mn should be below 0.02. Cubic-phase MnSe-rich precipitates have the sizes ranging from 50 nanometers to 1-5 micrometers. They are well dispersed in the PbSe-rich matrix, as round or layered microstructures. The mechanical properties of the nanocomposites can be determined by micro-hardness measurements. Interestingly, the average Vickers hardness values of the PbSe-MnSe nanocomposites are significantly improved, which are 16.6% and 51.6% harder respectively in x= 0.02 and 0.06 samples than those of pristine PbSe. Smaller Mn content can optimize the figure of merit ZT due to the band convergence and additional phonon scattering by precipitates, while higher Mn content has little influence on ZT because of the saturated Seebeck coefficient and anomalous increase in lattice thermal conductivity. As a result, the highest figure of merit is 0.52 at 712 K, which is achieved in the Pb0.96Mn0.02Na0.02Se sample. By further adjusting the Na content from 2% to 0.7%, the carrier concentration is optimized. Thus, the Seebeck coefficient and power factor become higher. A figure of merit of 0.65 is achieved at 710 K in the PbSe-MnSe nano-composite with a nominal composition of Pb0.973Mn0.02Na0.007Se. We suggest that further optimizing the electrical properties may achieve a higher thermoelectric performance in the PbSe-MnSe system.

Composition and Bioactivities of the Essential oil of Ixora finlaysoniana Wall. ex G. Don. (Family Rubiaceae)

The flowers of Ixora finlaysoniana Wall.ex. G. Don. grown in Egypt yielded 1.2 % and 2.4 % (v/w) of essential oil by hydrodistillation (HD) and solvent (diethyl ether) extraction (SE), respectively. GC-MS analysis revealed that the two oil samples were identical in some components, but differing in the composition and percentages of certain components. Twenty-two components were identified in both, representing 98.08 % and 95.19 %, respectively. Oxygenated compounds were dominant in HD oil, being 73.09 % compared with SE sample 26.77 %; while the hydrocarbons amounted to 24.99 % and 68.42 %, respectively. Ledol and sesquiterpene laurenene recorded highest percentage in HD sample15.23 % and 13.24 %; respectively. While; both hydrocarbons nonadecane and pentacosane are the major components in SE sample 24.70 % and 23.34 %; respectively. The two oil samples when compared to standard exhibited variable although significant efficacy and potency as antiulcer, anticonvulsant, antioxidant, chronic hypoglycemic and hepatoprotective; offering a support to recommendations of the possible utility of the oil of Ixora finlaysoniana as a potent drug in these activities.

Effect of Soxhlet Extraction Condition on Dewaxing Efficiency of the Beeswax-Treated Paper

In this study, the effect of soxhlet extraction on dewaxing of the aged beeswax-treated paper was examined. To do this, soxhlet extraction of the aged beeswax-treated paper performed with different reflux conditions and then measured the dewaxing efficiency and change in the various properties such as tensile strength, folding endurance, color and brightness. Also, an artificial aging test was executed in order to investigate the effect of soxhlet extraction on the preservability of the dewaxed paper. As the result of FT-IR analysis, a peak area of CH and COOH group, which are main band of beeswax, was decreased or removed after soxhlet extraction. The decreasing rate of each peaks were increased depending on reflux time. After dewaxing, the physical property such as MIT type folding endurance and tensile strength was decreased. And <TEX>$L^*$</TEX> value and brightness were increased while <TEX>$a^*$</TEX> and <TEX>$b^*$</TEX> value were decreased due to the remove of color compounds in beeswax. The more color deviation (<TEX>${\Delta}E$</TEX>) is expected with higher reflux times. As the result of artificial aging, preservability of two dewaxed papers except of DP_SE(C) sample was higher than that of untreated paper i.e. beeswax-treated paper.

Structure and Composition Analysis of Cu(In,Al)Se2 Thin Films Prepared by Rapid Thermal Selenization

Thin films of CuIn1-xAlxSe2 (CIAS) were prepared by stacked elemental precursor layers in an inert ambient. The stacking sequence of precursor layers may affect the kinetics of phase formation. The soda lime glass (SLG)/Cu/Al/In/Se sample heated at 750 °C for 30 s with a temperature ramp rate of 15 °C/s may react to form single-phase CIAS thin films with a chemical composition fairly close to the predetermined value. Transmission electron microscopy (TEM) analysis of a selenized film prepared at 600 °C revealed the segregation of the content of Al to the substrate side and a relatively large variation of Al distributed in a lateral direction as compared with those of other elements. Changing the Cu and Al layer sequence may affect the reaction paths and lead to the formation of a mixture of two CIAS quaternary phases with different compositions.

Effect of γ-ray radiation on electrical properties of heat-treated Tb x Sn1 − x Se single crystals

The effect of γ-ray radiation on the electrical properties of heat-treated Tb0.01Sn0.99Se (sample 1) and Tb0.05Sn0.95Se (sample 2) samples is studied. It is found that, as a result of irradiation with γ-ray 1.25-MeV photons, the charge-carrier concentration decreases in the temperature range T = 77−200 K by 17 and 6.3% for samples 1 and 2, respectively. It is assumed that, in the course of irradiation with γ-ray photons, terbium impurity atoms are located between sites of the crystal lattice; in addition, Frenkel defects are formed.

Ultrasonic Relaxation in Phase Transition Region in Ferroelectric Semiconductors of Sn&lt;sub&gt;2&lt;/sub&gt;P&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;6 &lt;/sub&gt;Family

The paper presents recent results of ultrasonic investigation of Sn2P2S6 family ferroelectric crystals and their solid solutions in the temperature range 100-300 K. It was shown that in Sn2P2(S,Se)6 crystals the critical ultrasonic velocity slowing down for longitudinal waves propagating along main crystallographic directions is quite sharp and large. The relative change of longitudinal ultrasonic velocity along z-axis at the phase transition gradually increased from 10 % in pure Sn2P2S6 till 25 % for sample with 0.4 content of Se. Such large velocity change causes the large ultrasonic attenuation anomaly. The increase of relaxation time: τ=τ0/(TC-T) leads to the increase of attenuation. Prefactor τ0 was shown to be very small and the critical attenuation anomaly arises in the narrow temperature range close to phase transition. In the 0.4 Se sample the phase transition is of the first order because small thermal hysteresis exists. The ultrasonic velocity behaviour in the ferroelectric phase was described using Landau theory and free energy expansion including sixth order terms. For (Sn,Pb)2P2S6 system the critical ultrasonic anomalies were smaller and the phase transition temperature substantially decreased (for 0.45 Pb sample the phase transition point was at Tc =140 K). The ultrasonic anomalies at phase transition in (PbxSn1-x)2P2S6 have large hysteresis showing that transition is of the first order, far from the critical point.

Selenium: Another metalloid beneficial for the electrochemical performance of Co electrode in alkaline rechargeable batteries

Many inactive materials have been found to be helpful for improving the electrochemical performance of Co electrode in alkaline rechargeable batteries, including B, P, Si, S, Si 3N 4, and BN. In this paper we find for the first time that selenium has a similar effect with them. Selenium incorporation is realized through a liquid-reduction method. The obtained Co–Se sample is investigated as the negative electrode material of alkaline rechargeable battery. Experimental results demonstrate that the Co–Se sample electrode shows excellent electrochemical reversibility and considerably high charge–discharge capacity, showing a great potential to enhance the electrochemical performance of Co-based alkaline rechargeable batteries. The electrochemical reaction mechanism and function mechanism of Se are also investigated.