Electrical Conductivity Coefficient Research Articles

The effect of the degree of sulphenylation on the stability of reduced graphene oxide nanofluids

Dispersion stability of nanoparticles in nanofluids is a prerequisite for allowing the nanofluids to act as convection heat transfer working fluids. This research prepared multiple types of sulfophenylated graphene (PSG) nanoparticles. Two samples subjected to different degrees of sulfophenylation were chosen to formulate different nanofluids with varying sulfophenylated particle concentrations. The nanofluids’ measured Zeta potential, electric conductivity, and thermal conductivity coefficients were used to investigate the stability. The research indicates the increase in the degree of sulfophenylation can improve the stability of nanofluids while exerting little influence on thermal conductivity; on the premise of ensuring stability, the number of nanoparticles added in base fluids can increase thermal conductivity. After that, high-sulfophenylated particle concentration nanofluids (2 mg/mL) were formulated using sulfonated-reduced graphene oxide (s-rGO) nanoparticles prepared to demonstrate excellent stability, and their thermal conductivity reached 0.773 W/m. K (55 °C).

Theoretical Study on the Influence of the Anharmonic Effect on the Ionic Conductivity and Thermal Stability of 8 mol% Yttria-Stabilized Zirconia Solid Electrolyte Material.

YSZ is a promising material for resistive memory devices due to its high concentration of oxygen vacancies, which provide the high anion migration rates crucial for the manifestation of resistance switching in metal oxides. Therefore, investigating the ionic conductivity of YSZ is an important issue. The ionic conductivity and thermal stability of 8 mol% YSZ were studied using the theories and methods of solid-state physics and physical chemistry. The impact of anomalous atomic vibrations on the material was also explored, and the variation in the ion vibration frequency, electrical conductivity, and thermal stability coefficient of electrical conductivity with temperature was obtained. The results show that the ion conductivity of an 8 mol% YSZ solid electrolyte increases nonlinearly with temperature, with a smaller increase at lower temperatures and a larger increase at higher temperatures. Considering the anharmonic effect of ion vibrations, the electrolyte conductivity is higher than the result of the harmonic approximation, and the anharmonic effect becomes more significant at higher temperatures. Our research fills the gap in the current literature regarding the theoretical non-harmonic exploration of the ion conductivity and thermal stability factor of YSZ solid electrolytes. These results provide valuable theoretical guidance for the development and application of high-performance YSZ resistive memory devices in high-temperature environments.

Abrasive Wear and Physical Properties of In-Situ Nano-TiCx Reinforced Cu–Cr–Zr Composites

Cu–Cr–Zr alloys reinforced in situ with TiCx nanoparticles were prepared via combustion synthesis and electromagnetic stirring casting. The microstructure of TiCx/Cu-Cr-Zr composites with various contents was analyzed. The microhardness and Brinell hardness of the composites were determined; the average volumetric abrasive wear rate and worn surface of the composites were investigated; and the electrical, thermal conductivity and thermal expansion coefficients of the materials were discussed. The results indicated that the addition of TiCx particles transformed the Cu–Cr–Zr matrix alloy microstructure from a dendritic to an equiaxed crystal, and the grain size was significantly refined as the amount added was increased. The composites with high TiCx content possessed higher hardness and abrasive wear resistance. The addition of TiCx particles reduced the electrical and thermal conductivity and thermal expansion coefficients of the materials.

Composition and thermoelectric properties of structures based on iron silicide grown by pulse laser deposition

Silicon compounds have a wide range of electrical properties. In particular, the possibility of creating thermoelectric converters based on them looks extremely attractive. The use of most silicides as thermoelectrics today is limited by their low efficiency. The development of approaches consisting in the creation of low-dimensional structures using non-equilibrium formation methods is one of the priority directions for improving the properties of thermoelectric generators. Determination of the effect of technological regimes on the structure, phase-chemical composition and thermoelectric properties of metal-silicide structures is a key task, the solution of which will allow creating highly efficient thermoelectric generators based on them. Thin-film structures with a layer thickness of ~50 nm formed at different growth temperatures by pulsed laser deposition on two types of substrates: sapphire and gallium arsenide coated with an Al2O3 nanolayer were studied in this work. On the formed samples, a chemical analysis and a study of the phase composition were performed. Chemical analysis was carried out by X-ray photoelectron spectroscopy with the chemical composition depth profiling. The phase composition was studied by Raman spectroscopy. In addition, analysis of the elements in the films was carried out by X-ray spectral microanalysis based on a scanning electron microscope. To determine the thermoelectric properties of the formed thin-film structures, the temperature dependences of the Seebeck coefficient and the electrical conductivity coefficient were recorded. The dependence of the thermoelectric characteristics of iron silicide films on the phase composition is analyzed. In particular, measurements of the thermoelectric properties of FeSix thin-film structures registered the manifestation of a strong thermoelectric effect in layers with the maximum number of chemical bonds between iron and silicon. The parameters of the growth process at which the most effective formation of iron-silicon chemical bonds is achieved were determined using the method of X-ray photoelectron spectroscopy. Line shifts from the beta phase of iron disilicide were found in the Raman spectra and the reasons for their appearance were proposed

A hybrid ceramic-based flexible thermoelectric nanogenerator with enhanced thermopower for human energy harvesting

The growing demand for power sources to run portable devices has led to the development of wearable energy-harvesting technology. The integration of wearable thermoelectric generators (WTEGs) into fabrics that can incessantly convert body heat into electricity has been researched extensively. Yet, commercial fabric-based wearable thermoelectric generators have not become conscious. In this study, a fabric-based flexible wearable thermoelectric device was designed using Cobalt doped ZnO nanorods via hydrothermal method as the n-type and Bi2Te3 nanostructures via dip coating method as the p-type and strips of each were connected to form TE legs. The structural and morphological analyses confirmed the formation of Co: ZnO and Bi2Te3 on the fabrics. The electrical conductivity and average Seebeck coefficient of Co:ZnO coated cellulose fabric were 4.80 S cm−1 and 390.5 µV/K. The device was fabricated and showed a device output voltage oscillating from ∼0.3 mV to ∼0.7 mV with a different human body temperature varying from 308 K to 309.4 K. The experimental data showed the output generated from the flexible device to be more suitable for energy harvesting from the human body and can be used in Biomedical sensing applications.

Thermodynamics Properties of (6, 6, 12)-Graphyne Structure Due to Biaxial Strain and Magnetic Field Effects

In this paper, we apply a tight binding Hamiltonian model in the presence of magnetic field for investigation of the electronic and transport properties of (6, 6, 12)-graphyne layer. We have also considered the effects of in-plane biaxial strain on the electronic behavior of (6, 6, 12)-graphyne layer. Moreover the impact of strains on magnetic susceptibility and specific heat of the structure has been studied. Specially, the temperature dependence of static thermal conductivity of (6, 6, 12)-graphyne layer has been studied due to magnetic field and strain effects. We have exploited the linear response theory and Green’s function approach to obtain the temperature behavior of thermal conductivity, electrical conductivity and Seebeck coefficient. Our numerical results indicate, thermal conductivity increases upon increasing the temperature in the low amounts region. This fact comes from the increasing of thermal energy of charge carriers and excitation of them to the conduction bands. The temperature dependence of Seebeck coefficient shows that the thermopower of undoped (6, 6, 12)-graphyne layer gets positive sign on the whole range of temperatures in the absence of strain effects. The effects of both electron doping and magnetic field factors on temperature behavior of electrical conductivity of (6, 6, 12)-graphyne have been investigated in details. Moreover the effects of biaxial strain on thermal conductivity of single layer (6, 6, 12)-graphyne have been addressed.

Green electromagnetic interference shielding films with unique and interconnected 3D magnetic/conductive interfaces

Magnetic nanoparticle-decorated biomass-derived carbon films are intriguing green electromagnetic interference shielding composites because of their eco-friendly, high shielding effectiveness, low reflection loss, etc. However, it is still difficult to uniformly decorate magnetic nanoparticles onto a whole interconnected carbon skeleton. Herein, to overcome this difficulty, a novel in situ coprecipitation approach was developed to construct the 3D Fe3O4@carbon core-shell network with interconnected magnetic/conductive interfaces. Briefly, common filter papers (CFPs) decorated with metal ions were immersed into ammonia solutions, to in situ generate Fe3O4 nanoparticles on whole CFPs. Subsequently, Fe3O4-decorated CFPs are carbonized to obtain magnetic and conductive biomass-derived carbon films. The novel structure endows the resultant films with excellent electrical conductivity (673–732 S/m), excellent shielding (30.6 dB) and low reflection coefficient (R = 0.354). The specific SE of our films is as high as 191.3 dB/mm, exceeding that of the reported biomass-derived carbon materials.

Conductivity, thermoelectric, and magnetic properties of pavonite homologue In0.45Mn2.17Bi3.38Se8 with N = 3

Pavonite homologues are semiconductors that show potential for thermoelectric applications. Herein, we report the synthesis of a quaternary selenide, In0.5Mn2Bi3.5Se8, that exhibits good thermal stability below 1032 K. Whereas most pavonite compounds exhibit the metallic properties of degenerate semiconductors, In0.45Mn2.17Bi3.38Se8 possesses a band gap of 0.85 eV. In addition, its electrical conductivity and Seebeck coefficient exceed 3 S/cm and 300 μV/K at 810 K, respectively, with the compound mainly displaying semiconductor properties. In0.45Mn2.17Bi3.38Se8 exhibits paramagnetism at room temperature followed by a paramagnetic-to-antiferromagnetic transition at ∼10.2 K. Our findings enrich the current understanding of the pavonite homologous series, providing useful insight for future exploration in related fields.

Realizing the thermoelectric performance in cobalt doped p-CuO semiconductor by valance band flattening and effective phonon scattering approach

In this work we investigated the thermoelectric properties of CuO microcrystals through band structure modification and effective scattering of charge carriers and phonons. Synergetic improvement in carrier concentration, band effective mass and magnetic moment of CuO through ferromagnetic cobalt doping has extensive impact for the simultaneous increase of electrical conductivity and Seebeck coefficient. Band conduction model was employed to study the conduction mechanism in detail. Modification in the electronic band structure through band flattening results average S2σ of 5.52 μW/mK2 in the temperature range of 300–873 K for an optimum doping level of 0.5 at% of Co, this is 3.5 times superior to undoped CuO. Moreover enormous phonon scattering centers such as point defects suppressed the lattice thermal conductivity from 4.43 W/mK to 1.92 W/mK at 873 K. These viable strategies aided to enhance the thermoelectric efficiency of our prepared samples to efficiently utilize non-exploited thermal energy into green energy production.

Synthesis and investigation of physical properties of CNT/Ni0.5Zn0.5Fe2O4 nanocomposites with low density

Ni-Zn ferrites have important applications in the field of soft magnetic materials due to their excellent magnetic properties, but their high bulk density hinders their widespread use. CNT/nickel-zinc ferrite (CNT/Ni0.5Zn0.5Fe2O4) nanocomposites was prepared by sol-gel method, and sintered at 1000 °C to be used as an electromagnetic wave absorber. The results showed that the morphology, impedance matching, density, electrical conductivity and absorption coefficient of CNT/Ni-Zn ferrite was controlled by the additional CNT content. The NZ3 sample containing 0.06 g of CNT showed high conductivity, and high absorption coefficient. The amount of 0.06 g of CNT was a critical amount for the CNT/Ni-Zn ferrite nanocomposites. Above this value, the increasing trend toward improved nanocomposite properties due to the agglomeration of CNTs was reversed. The absorption performance of the CNT/Ni-Zn ferrite nanocomposites are attributed to the incorporation of dielectric and magnetic loss mechanisms in which the magnetic portion is comparable to the dielectric portion. Possessing excellent magnetic and absorption properties, it has the potential to be an excellent electromagnetic wave absorbing material.

Unveiling the mechanical and dynamical stability to the contribution of transport properties of FeNbSb: A first principle approach

This study adopts first principle calculations to probe the electronic, elastic, vibrational, and transport properties of FeNbSb Alloys. The elastic and phonon properties were deduced to explain the stability and dynamical nature of FeNbSb alloy. Voigt-Reuss-Hill approximation was used for the mechanical properties, Poisson's ratio for brittleness, while Pugh's rule was used to estimate the alloy ductility. Besides, the absence of negative frequency revealed the dynamical stability of FeNbSb. Also, the thermal conductivity, electrical conductivity, power factor, and Seebeck coefficient were estimated in terms of energy relative to the Fermi level at 300K≤T≤800K. The study achieved a power factor of 15×1011μW/cmK2s and a maximum zT of 0.52 at 800K for FeNbSb. In conclusion, the result of this study suggests that FeNbSb p-type is a suitable material for thermoelectricity.

Progress in theoretical study of lead-free halide double perovskite Na2AgSbX6 (X = F, Cl, Br, and I) thermoelectric materials

Herein, we have studied progressively novel metal lead-free halide double perovskite renewable energy materials. Due to their potential use in electronic devices, researchers have investigated these materials with a lot of interest. From the electronic structure, we have found that these are the indirect band gap semiconductors within the range between 1.273 and 3.986eV. Optical parameters such as dielectric constant, electrical conductivity, and absorption coefficient have also been investigated, which have shown that these materials have potential use in photovoltaics. We have checked stability issues by thermodynamic parameters and phonon spectra. We have found them thermally stable; however, the phonon spectra show their dynamical instability and except for Na2AgSbF6 and Na2AgSbI6, the remaining compounds are weak in mechanical stability. For another futuristic purpose, thermoelectric parameters such as Seebeck coefficient, power factor, and figure of merit have also been calculated, which again verifies that these materials may be very useful in thermoelectric devices. Most of the parameters have been computed for the first time. We have performed this computational work using WIEN2k simulation code, which is based on the full-potential linearized augmented plane wave (FP-LAPW) technique. It is one of the most reliable techniques to calculate the photovoltaic properties of semiconducting perovskites. The interaction between ion-core and valence electrons was dealt with within the PAW technique as implemented in Vienna Ab initio Simulation Package (VASP).

Boosting thermoelectric performance of conjugated polymers via interchain molecular docking: Significance of highly crystalline and percolated morphology

The development of organic materials with high thermoelectric performance requires the exploration of organic molecules having various structures and a deep understanding of the relationship between their structure and thermoelectric properties. In this study, a series of donor–acceptor-type conjugated copolymers with an isoindigo (IID) unit as a building block are synthesized and compared to investigate the effect of the molecular structure of the IID-based conjugated polymers on the microstructure and thermoelectric properties of polymer films. The crystallinity and molecular packing of the polymers change significantly depending on the symmetry of the donor unit copolymerized with the IID unit, resulting in considerable differences in the doping and charge transport characteristics of the polymers. Importantly, the polymer with high crystallinity and fibril-like crystalline network shows excellent thermoelectric performance, exhibiting a high power factor of 212 µW m−1 K−2 upon doping; this is attributed to the high electrical conductivity and high Seebeck coefficient, which result from its highly ordered structure. This study not only demonstrates the potential of the IID unit as a promising building block for high-performance conjugated polymers for thermoelectric applications but also provides important guidelines for the design of IID-based polymers having high thermoelectric performance.

Microstructure, domain structure, ferroelectric and piezoelectric properties of textured bismuth-containing ceramics

In this report, the processes of texture formation in grain-oriented ferroelectric ceramics based on layer-structured ferroelectric Bi4Ti3O2 (LSBT) prepared by hot forging method are considered. The microstructural and X-ray methods revealed the axial textured formation in ferroelectric ceramic that are used to estimate the orientation factor of ceramics. For the first time, the domain structure changes when poling the anisotropic ferroelectric ceramics are investigated. The anisotropy of electromechanical, piezoelectric and ferroelectric properties of ferroelectric ceramics due to the crystal texture existence in it is studied. The aim of this study is to study the processes of crystalline texture formation in polycrystalline BLSF and to establish the dependence of the electrophysical properties of ceramics on the degree of texturing. Ceramics were textured using the hot stamping (HS) method developed at the Research Institute of Physics. The mechanism of the method is that the workpiece is subjected to uniaxial pressure and free radial deformation occurs due to the plastic flow of the material until the workpiece fills the free volume of the mold, which is created by placing the workpiece in the mold with a gap. The study of the microstructure of ceramics showed that an increase in the firing temperature in the range 950–1050[Formula: see text]C causes a sharp decrease in porosity and increases the density to 7.95 g/[Formula: see text], which is 98% of theoretical. An X-ray analysis was performed and microstructural studies were carried out, which revealed the formation of an axial texture in ceramics. The features of the switching processes of textured ceramics are revealed. The characteristics of the polarization switching of ceramics in the directions parallel and perpendicular ([Formula: see text]) of the pressure axis during hot processing were obtained from the dielectric hysteresis [Formula: see text]([Formula: see text]) loops, i.e., axis axial texture. The [Formula: see text]-cut ceramics are characterized by a more complete polarization switching, which is associated with the additional orientation of the (001) crystallographic planes in the textured material, as well as the presence of a threshold switching field. In the temperature range from -196 to + 600[Formula: see text]C, the anisotropy of the electro physical properties of ceramics due to the presence of a crystalline texture in it was studied. The dielectric constant, electrical conductivity, piezoelectric and elastic coefficients were measured for sections of ceramics of different orientations relative to the axis of the texture. The anisotropy of the dielectric constant and electrical conductivity manifests itself weakly at room temperature and increases sharply when approaching the Curie temperature. In the temperature range +20–400[Formula: see text]C, the high thermal stability of the piezoelectric module [Formula: see text], measured by the quasistatic method, was established.

In-doping induced resonant level and thermoelectric performance enhancement in n-type GeBi2Te4 single crystals with intrinsically low lattice thermal conductivity

Resonant level, the impurity level located inside the valence/conduction band, is an effective strategy for decoupling the electrical conductivity and Seebeck coefficient and enhancing the thermoelectric power factor. In this work, we show that In doping induces resonant level and enhances the thermoelectric performance of GeBi2Te4, a promising n-type thermoelectric material with layered structure. Single crystals grown by Bridgman method were used in this study to take the advantage of its anisotropic transport properties. An ultralow lattice thermal conductivity of ∼0.51 W m−1 K−1 at 323 K was found along the c-axis of GeBi2Te4, driven by intrinsic cation disorder and the low phonon group velocity from the relatively weak chemical bonds as well as the strong lattice anharmonicity caused by hierarchical bond orders. Both enhanced electrical conductivity and Seebeck coefficient were observed in the In-doped samples, indicating that In-doping not only increases the carrier concentration, but also introduces the resonant level that was further confirmed by the first-principles calculation. A maximum zT of ∼0.42 at 523 K and an average zT of 0.36 over 323 to 573 K were achieved in Ge0.97In0.03Bi2Te4 crystal sample, ∼100% and ∼89% enhancement compared to those of pristine single crystal sample, respectively. This study demonstrates another example of resonant level for thermoelectric performance enhancement, which may be applied to other related materials.

Enhancement of thermoelectric properties of transition metals, nickel and copper dually doped ZnO

Thermoelectricity is one of the potential sustainable energy sources, that can be treated as a remedy for the present energy scarcity as it is a clean-green technology. ZnO is a promising multifunctional metal oxide and its thermoelectric conversion property is highly exploited in the field of waste heat recovery. Herein, the impact of nickel and copper substitution on the thermoelectric properties of ZnO is investigated. The structural and morphological analysis of the doped materials confirmed the hexagonal wurtzite structure of ZnO. The strain induced in the lattice and the variation of crystallite size established the substitution of the dopants into the host matrix. The optical band gap energy shows a reduction from 3.1 eV to 2.15 eV with a redshift in the absorption edge. The electrical conductivity and Seebeck coefficient of ZnO increased upon doping. The most remarkable result of nickel and copper doping is the enhancement of the Seebeck coefficient to 1318 µV/K. As a result of the lattice distortion created due to the dual substitution of the dopants, the thermal conductivity is considerably reduced to 8.36 W/mK. The power factor enhancement and degradation of thermal conductivity give rise to a six-fold increase in the thermoelectric figure of merit of the material.

Impact of Zn-doping on the thermoelectric properties of Bi2Te2.7Se0.3 nanostructures synthesized by hydrothermal method

Studies on Zn doping of thermoelectric materials are actively conducted; however, doping of Zn in solution synthesis remains a challenge. In this study, a hydrothermal approach was utilized to synthesize Bi2Te2.7Se0.3 (BTS) and dope with Zn. Zn was successfully incorporated into the BTS structure, and the hot-pressed Zn-doped BTS powder exhibited a layered structure with micrometer-scale crystals. BTS exhibited inherent semiconductor properties, while the Zn-doped sample exhibited degenerate semiconductor characteristics, which affected the electrical conductivity and Seebeck coefficient. Based on the σ and S values, doping with 0.3 mol Zn was determined to be the optimal condition for enhancing the thermoelectric power factor. This study offers important contributions to the development of solution-based doping of BTS thermoelectric materials for energy harvesting and cooling applications.

Tuning band structure and texture for improved thermoelectric performance in BiSe

Layer-structured BiSe has emerged as a promising Te-free thermoelectric (TE) material because of its intrinsic low thermal conductivity. Herein we report the optimization of TE performance for BiSe through In doping to tune the band structure and the proper annealing treatment to adjust the texture. The first-principles calculations and doping experiments reveal that In dopant in BiSe introduces additional energy levels near Fermi level leading to the increase of carrier effective mass. The preferred orientation of (00l) plane in BiSe was well adjusted to optimize the electrical conductivity and Seebeck coefficient. Through tuning band structure and texture simultaneously, the Bi0.995In0.005Se sample exhibited a maximum figure of merit ZT value of 0.33 at 523 K, which is about 43.5 % higher than that of the pristine BiSe sample without the texture adjustment. This work presents a potential route to promote the TE performance of layer-structured materials.

Preparation and Characterization of Diamond-like Carbon Coatings for Biomedical Applications-A Review.

Diamond-like carbon (DLC) films are generally used in biomedical applications, mainly because of their tribological and chemical properties that prevent the release of substrate ions, extend the life cycle of the material, and promote cell growth. The unique properties of the coating depend on the ratio of the sp3/sp2 phases, where the sp2 phase provides coatings with a low coefficient of friction and good electrical conductivity, while the share of the sp3 phase determines the chemical inertness, high hardness, and resistance to tribological wear. DLC coatings are characterized by high hardness, low coefficient of friction, high corrosion resistance, and biocompatibility. These properties make them attractive as potential wear-resistant coatings in many compelling applications, including optical, mechanical, microelectronic, and biomedical applications. Another great advantage of DLC coatings is that they can be deposited at low temperatures on a variety of substrates and can thus be used to coat heat-sensitive materials, such as polymers. Coating deposition techniques are constantly being improved; techniques based on vacuum environment reactions are mainly used, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). This review summarizes the current knowledge and research regarding diamond-like carbon coatings.

Comparative Thermoelectric Properties of Polypropylene Composites Melt-Processed Using Pyrograf® III Carbon Nanofibers

The electrical conductivity (σ) and Seebeck coefficient (S) at temperatures from 40 °C to 100 °C of melt-processed polypropylene (PP) composites filled with 5 wt.% of industrial-grade carbon nanofibers (CNFs) is investigated. Transmission Electron Microscopy (TEM) of the two Pyrograf® III CNFs (PR 19 LHT XT and PR 24 LHT XT), used in the fabrication of the PP/CNF composites (PP/CNF 19 and PP/CNF 24), reveals that CNFs PR 24 LHT XT show smaller diameters than CNFs PR 19 LHT XT. In addition, this grade (PR 24 LHT XT) presents higher levels of graphitization as deduced by Raman spectroscopy. Despite these structural differences, both Pyrograf® III grades present similar σ (T) and S (T) dependencies, whereby the S shows negative values (n-type character). However, the σ (T) and S (T) of their derivative PP/CNF19 and PP/CNF24 composites are not analogous. In particular, the PP/CNF24 composite shows higher σ at the same content of CNFs. Thus, with an additionally slightly more negative S value, the PP/CNF24 composites present a higher power factor (PF) and figure of merit (zT) than PP/CNF19 composites at 40 °C. Moreover, while the σ (T) and S (T) of CNFs PR 19 LHT XT clearly drive the σ (T) and S (T) of its corresponding PP/CNF19 composite, the S (T) of CNFs PR 24 LHT XT does not drive the S (T) observed in their corresponding PP/CNF24 composite. Thus, it is inferred in PP/CNF24 composites an unexpected electron donation (n-type doping) from the PP to the CNFs PR 24 LHT XT, which could be activated when PP/CNF24 composites are subjected to that increase in temperature from 40 °C to 100 °C. All these findings are supported by theoretical modeling of σ (T) and S (T) with the ultimate aim of understanding the role of this particular type of commercial CNFs on the thermoelectrical properties of their PP/CNF composites.