Electrical Transport Behavior Research Articles

Nanostructured Te‒SnTe eutectic composites with enhanced thermoelectric performance

The eutectic Te‒SnTe composites were successfully prepared via a melt spinning method combined with a spark plasma sintering technique. The differences in thermoelectric properties for alloys near the eutectic composition were investigated. These composites could benefit from both the higher electrical conductivity of the SnTe phase and the superior Seebeck coefficient of the Te phase. The eutectic Sn-90at%Te composite exhibits an enhanced thermoelectric performance. Its maximum ZT is 1.8–2.1 times higher than that of pristine SnTe and Te materials. Upon doping with the Sb element, the electrical transport behavior could be further improved. Large amounts of grain boundaries and phase interfaces can readily scatter phonons. Combined with the extra scattering from nanoprecipitates, dislocations, and strain fields, an ultralow lattice thermal conductivity of 0.49 W m−1 K−1 could be obtained for the Sn-90at%Te-2.0at%Sb alloy at 633 K. The improved thermoelectric properties for the Te‒SnTe eutectic system provide a new strategy to explore high-performance materials.

Influence of sintering temperature on the structural, electrical transport and magnetic behaviour of La0.7Sr0.3MnO3 prepared through co-precipitation technique

In this communication, report of nanostructured polycrystalline La0.7Sr0.3MnO3 (LSMO) prepared through a co-precipitation technique at 800 °C, 900 °C and 1000 °C is discussed in detail. The structural, electrical transport, magnetoresistance and magnetic properties of LSMO samples were found strongly dependent on the sintering temperature (TS). Structural properties were studied through XRD and SEM. The results of Rietveld refined XRD data show that all the samples are in tetragonal arrangement and having single-phase structure with space group I4/mcm (140). The average size of synthesized nanoparticles was found increasing (21.05 nm to 46.06 nm) with increase in sintering temperature. A significant increase in metal–insulator transition temperature (TMI) was observed at higher sintering temperatures. Higher sintering temperature results in the enhancement of resistivity. To understand the metallic part of resistivity (T < TMI) including upturn behavior, resistivity data with and without magnetic field were fitted using Kondo like spin-dependent scattering, electron–electron (e-e), electron–phonon (e-p) and electron-magnon (e-m) scattering. The decrement in magnetoresistance (MR) in the wide temperature range has been explained by spin-polarized tunnelling in this communication. Magnetic properties were examined through M−H measurements and found the highest value of magnetization for the sample sintered at 1000 °C.

Relative contributions of the electron-lattice and the electron-spin scatterings to the giant baroresistance effect in Ni–Co–Mn–In system

The evolutions of electrical transport property and Baroresistance (BR) effect at the martensitic transformation (MT) with the change of Co content have been systematically investigated in the Ni50-xCoxMn35In15 (0 ≤ x ≤ 7) Heusler system. The structure measurements show that every sample undergoes first-order MT from a L21 cubic structure to a 3 M monoclinic structure. According to magnetic measurements, it is also found that the samples with lower Co content (0 ≤ x ≤ 3) exhibit a paramagnetic MT, i.e. the MT occurs between the paramagnetic austenite and the paramagnetic martensite. At higher Co content, however, the samples display a metamagnetic MT, i.e. the MT occurs between the ferromagnetic austenite and the paramagnetic martensite. Due to the enhancement of the ferromagnetic ordering for the austenitic phase with Co increasing, the difference in resistivity between austenitic and martensitic phases is enlarged significantly. This leads to a giant BR effect with a value of ∼250% associated with the hydrostatic pressure-induced MT can be observed in the sample with x = 6. Moreover, the Hall measurement results indicate that the difference in electrical transport behavior between both phases for the studied alloys mostly relies on the mobility of carriers related to the electro-lattice and the electro-spin scatterings. In this case, the underlying mechanism of the relative contributions originating from these two different scattering processes to the saturated BR effect has been separated quantitively based on the electrical transport measurements under applied different hydrostatic pressures. It demonstrates that the electron-spin scattering acts as a dominant role in improvement of the BR effect for this system.

Structural, magnetic, and electrical properties of Ti-doped La0.7Ba0.3Mn1-xTixO3 (0≤ x≤0.3) ceramics

The effect of Ti substitution at the Mn site on the structural, magnetic, and electrical properties of La0.7Ba0.3Mn1-xTixO3 (0≤x≤0.3) ceramics is studied. Samples are synthesized via a conventional solid-state reaction route. The analysis of X-ray diffraction data by using the FullProf Rietveld software confirms the phase transformation of these samples from an orthorhombic phase (0≤x≤0.1) to a rhombohedral one (0.2≤x≤0.3). The pristine sample (x = 0) undergoes paramagnetic to ferromagnetic transition characterization at the Curie temperature (TC) of 352 K and metal–insulator transition characterization at the transition temperature of 287 K. Partial substitution of Ti at the Mn site will not only decrease TC but is also expected to tune the electrical transport behavior of the system. Metal–insulator transition exists only in x = 0, x = 0.02, and x = 0.05 samples. By contrast, fully insulating behavior is observed in three remaining samples. The observed rapid decrease in TC could result from non-ferromagnetic Ti ions, which weaken the double-exchange interaction. The electrical resistivity data in metallic and insulating regions are analyzed using various conduction models. The nature of electronic transport in La0.7Ba0.3Mn1−xTixO3 (0.1 ≤ x ≤ 0.3) is studied.

Photon irradiation effects on electrical properties of n-ZnO/p-Si junctions for optoelectronic device

Simple high energy laser photon irradiation is a handy tool to tune the functional properties of wide band gap oxide-based devices. Present study reports on the effects of laser photon irradiation on electrical transport behaviour of n -ZnO/ p -Si p-n junctions. The n- type conductivity of ZnO was optimised by doping of stoichiometric amount of Al in ZnO. The n -ZnO/ p -Si junctions were grown on p -Si (100) substrate by pulsed laser deposition. The structural property was analysed by X-ray diffraction. Morphological study was done using atomic force microscopy (AFM) which shows smooth and mono-dispersed surfaces of the p-n junction. The current-voltage ( I-V ) characteristic of the n -ZnO/ p -Si devices have been measured at room temperature in the dark and under illumination. Moreover, the effects of 532 nm visible laser light irradiation on the electric parameter of n -AZO/ p -Si p-n junctions were investigated. The characteristic parameters of the junctions such as barrier height, ideality factor and series resistance were determined from the current-voltage measurement. The results show a promise of ZnO based diode structure for its optoelectronic applications.

Geometrical Structure Optimization Design of High-Performance Bi2Te3-Based Artificially Tilted Multilayer Thermoelectric Devices

Artificially tilted multilayer thermoelectric devices (ATMTDs) are a kind of thermoelectric device that can directly convert heat into electricity based on transverse thermoelectric effect. Although the devices have a simplified multilayer structure, their geometrical optimization is a complicated task. In this work, n-type Bi2Te2.7Se0.3 and p-type Bi0.1Sb1.9Te3 materials, which have the most important commercial applications in conventional thermoelectric devices, were selected as the component materials to assemble a promising high-performance Bi2Te3-based ATMTD. A numerical analysis method was employed to optimize the device length, device width, and thickness of the component materials. The results revealed that a large device width/length ratio, a small device aspect ratio, and a small thickness of component materials are favorable for achieving a high conversion efficiency. The temperature and charge distributions inside the ATMTD are studied based on finite element simulation. The nonuniform distribution of temperature field inside the device strongly depends on the thermal conductivity of component materials. The accumulation of a transverse electric field, accompanied with the cancellation of longitudinal electric field, is a consequence of different electric field distributions in the two component materials. This work provides a better understanding on the anisotropic electrical and thermal transport behaviors in transverse thermoelectric devices.

Tuning Electrical Conductance in Bilayer MoS2 through Defect-Mediated Interlayer Chemical Bonding.

Interlayer interaction could substantially affect the electrical transport in transition metal dichalcogenides, serving as an effective way to control the device performance. However, it is still challenging to utilize interlayer interaction in weakly interlayer-coupled materials such as pristine MoS2 to realize layer-dependent tunable transport behavior. Here, we demonstrate that, by substitutional doping of vanadium atoms in the Mo sites of the MoS2 lattice, the vanadium-doped monolayer MoS2 device exhibits an ambipolar field effect characteristic, while its bilayer device demonstrates a heavy p-type field effect feature, in sharp contrast to the pristine monolayer and bilayer MoS2 devices, both of which show similar n-type electrical transport behaviors. Moreover, the electrical conductance of the doped bilayer MoS2 device is drastically enhanced with respect to that of the doped monolayer MoS2 device. Employing first-principle calculations, we reveal that such striking behaviors arise from the presence of electrical transport networks associated with the enhanced interlayer hybridization of S-3pz orbitals between adjacent layers activated by vanadium dopants in the bilayer MoS2, which is nevertheless absent in its monolayer counterpart. Our work highlights that the effect of dopant not only is confined in the in-plane electrical transport behavior but also could be used to activate out-of-plane interaction between adjacent layers in tailoring the electrical transport of the bilayer transitional metal dichalcogenides, which may bring different applications in electronic and optoelectronic devices.

Antiphase Boundaries as Faceted Metallic Wires in 2D Transition Metal Dichalcogenides.

Antiphase boundaries (APBs) in 2D transition metal dichalcogenides have attracted wide interest as 1D metallic wires embedded in a semiconducting matrix, which could be exploited in fully 2D‐integrated circuits. Here, the anisotropic morphologies of APBs (i.e., linear and saw‐toothed APBs) in the nanoscale are investigated. The experimental and computational results show that despite their anisotropic nanoscale morphologies, all APBs adopt a predominantly chalcogen‐oriented dense structure to maintain the energetically most stable atomic configuration. Moreover, the effect of the nanoscale morphology of an APB on electron transport from two‐probe field effect transistor measurements is investigated. A saw‐toothed APB has a considerably lower electron mobility than a linear APB, indicating that kinks between facets are the main factors of scattering. The observations contribute to the systematical understanding of the faceted APBs and its impact on electrical transport behavior and it could potentially extend the applications of 2D materials through defect engineering to achieve the desired properties.

The realization of insulator-metal transition in a p-type metastable ZnSb by dual-phase nanostructure

Insulator-metal transition (IMT) in a metastable phase of ZnSb-based films has been explored systematically. It is found that the reduction of thickness contributes to the precipitation of metastable structure and induces a wide controllable temperature span for the presence of metastable ZnSb phase, resulting in thickness dependent IMT of p-type ZnSb film during annealing process. The metastable structure can be obtained without any void generation after erbium-filling by the formation of crystalline/crystalline dual-phase nanostructure, which can improve the electrical transport and trigger IMT behavior with the temperature of 430 °C, providing a strategy for realizing multi-level data storage.

Magnetic property under the pressure and electrical transport behavior under the magnetic field for the perovskite manganite La0.7Ca0.3MnO3

Abstract With respect to the magnetic properties under the pressure for the ferromagnetic metallic system La1−xCaxMnO3(0.18 ≤x

Dielectric response and magneto-electric interaction of La1.67Sr0.33NiO4 single crystal

The dielectric response of La1.67Sr0.33NiO4 single crystal varies with the frequency, temperature and magnetic field has been investigated. Experimental results show that the dielectric constant reaches 104 at high temperature region, and the low temperature dielectric behavior confirms that the electrical transport behavior follows a variable-range-hopping (VRH) model. The dielectric behavior varies with the external magnetic field where the magnetic field induced phase transition of charge order (CO) is companied with the change of the dielectric behavior, indicating a magnetoelectric properties of the charge ordered compound of La1.67Sr0.33NiO4. Therefore, the coexistence of Ni3+ and Ni2+ ions makes the CO, which responds orderly at high temperature under the action of external magnetic field may contributed to the observed magnetodielectric behavior.

Understanding the dielectric and electrical transport behaviors of plasma polymerized diethanolamine thin films under alternating electric field

A capacitively coupled parallel plate glow discharge reactor has been utilized to develop plasma polymerized diethanolamine (PPDEOA) thin films to look into the alternating current (AC) features of PPDEOA thin films. It is observed that the dielectric constant, ɛ′ in PPDEOA thin films enhances by declining the frequency and that increases with increasing temperature. The AC electrical conductivity, σac is frequency dependent. The frequency exponent, s values are found to be 0.32 to 1.0 and 1.0 to 1.8 in the lower (102–103 Hz) and higher (>103 Hz) frequencies, respectively. These suggest the presence of hopping conduction in the lower frequency region and other mechanisms in the higher frequency region. The activation energies are derived to be 0.03 to 0.28 eV illustrating the less effect of temperature on them. The real part, M´ and imaginary part, M ̋ of electric modulus vary with frequency. The frequency dependent loss tangent, tanδ is obtained. The ɛ′, σac , and tanδ deviate by the virtue of film thicknesses.

Thermoelectric Properties of Nano‐grained Mooihoekite Cu9Fe9S16

Cu‐Fe‐S‐based compounds gain the interest from thermoelectric community because all the consisting elements, Cu, Fe, and S, are non‐toxic and earth‐abundant. Comparing with CuFeS2 and Cu5FeS4, the investigation on Cu9Fe9S16 is very rare. In this work, a series of Cu9–xFe9+xS16 samples were fabricated by means of melting‐annealing process. Their phase composition, microstructure, electrical and thermal transport properties were systematically investigated. X‐ray measurement confirms that all samples are phase pure. Transmission electron microscopy characterization indicates that the fabricated Cu9Fe9S16 has a natural nanostructure. Cu9Fe9S16 shows semiconducting‐like electrical transport behavior and intrinsically low lattice thermal conductivity. Beyond the numerous boundaries between nanosized grains, the existence of low‐frequency optical phonons is also responsible for the intrinsically low lattice thermal conductivity. Doping Fe at the Cu‐sites in Cu9Fe9S16 significantly alters the electrical transport properties by introducing extra carriers. A peak dimensionless figure of merit zT value of 0.21 is obtained at 800 K for pure Cu9Fe9S16, which is comparable with that for CuFeS2.

Synthesis and Physical Properties of Antiperovskite CuNFe3 Thin Films via Solution Processing for Room Temperature Soft-Magnets

Antiperovskite CuNFe3 (CNF) thin films have been successfully prepared by chemical solution deposition (CSD) for the first time. They are versatile in many applications as an iron-based nitride. The preparation of pure CNF thin films is a challenging work for the complexity of the phase diagram. Herein, the CNF thin films are phase-pure and polycrystalline. Annealing temperature effects on the microstructures and physical properties were investigated, showing that the CNF thin films are metallic and can be considered as a candidate for room temperature soft-magnets with a large saturated magnetization (Ms) and a low coercive field (Hc). At high temperatures, the electrical transport behavior of CNF thin films presents a low temperature coefficient of resistivity (TCR) value, while the electron–electron interaction is prominent at low temperatures. The reported solution methods of CNF thin films will enable extensive fundamental investigation of the microstructures and properties as well as provide an effective route to prepare other antiperovskite transition-metal nitride thin films.

Solution Processable CrN Thin Films: Thickness-Dependent Electrical Transport Properties.

Thickness is a very important parameter with which to control the microstructures, along with physical properties in transition-metal nitride thin films. In work presented here, CrN films with different thicknesses (from 26 to 130 nm) were grown by chemical solution deposition. The films are pure phase and polycrystalline. Thickness dependence of microstructures and electrical transport behavior were studied. With the increase of films thickness, grain size and nitrogen content are increased, while resistivity, zero-field sensitivity and magnetoresistance are decreased. In the temperature range of 5–350 K, all samples exhibited semiconductor-like properties with dρ/dT < 0. For the range above and below the Néel temperature, the resistivity can be fitted by the thermal activation model and the two-dimensional weak localization (2D-WL) model, respectively. The ultra-low magnetoresistance at a low temperature under high magnetic fields with a large zero-field sensitivity was observed in the CrN thin films. The zero-field sensitivity can be effectively tuned to 10−2 K−1 at 5 K with a magnetoresistance of less than 1% at 2 K under 14 T by reasonably controlling the thickness.

Magnetic field-induced metamagnetic, magnetocaloric and pyrocurrent behaviors of Eu2CoMnO6

In this paper, the structural, transport, pyrocurrent and magnetic behaviors of Eu2CoMnO6 (ECMO) sample are reported. It was prepared by the solid-state reaction method and crystallized in monoclinic crystal structure with a space group of P21/n. A systematic study of the temperature and magnetic field-dependent susceptibility revealed a complex magnetic behavior with field-induced type-II metamagnetic phase transition of the first-order. The multiple sharp jumps in the initial magnetization curve for T < 10 K could be attributed to structural distortion related to the martensite-like strains from E*-type antiferromagnetic to ferromagnetic ordering. The metastable magnetic behavior for T ≥ 60 K is ascribed to a transformation of the low-field disordered spin glass phase to long-range ordered ferromagnetic phase, induced by critical fields. These critical fields are quite sensitive to the direction and magnitude of the field-cooling process. The temperature-dependent magnetocaloric effect with maximum value of ~3.3 J kg−1K−1 at TC ~ 123 K and the electrical transport behavior of ECMO were studied. Further, temperature dependent pyroelectric current and polarization data of ECMO are investigated.

Structural and electrical properties of Mg Silicide thin films deposited by RF sputtering

Mg2Si based thin films are a promising candidate for thermoelectric applications in the mid temperature range. The main advantages of these films are their low density, abundance of the elements used, good stability and environmental friendly nature. Nano structuring is considered to be useful tool to enhance the properties and hence thin films have been studied; although fabrication of Mg2Si thin film has been difficult due to difference in properties of magnesium and silicon. Semiconducting Mg2Si thin films were deposited on silicon substrate by radio frequency magnetron sputtering at low substrate temperature following a distinct approach. X-ray diffraction (XRD) and Field – Emission Scanning Electron Microscopy (FE-SEM) with EDS were done to study the phases, elemental composition and microstructure of these films. XRD results showed single phase Mg2Si formation. SEM results revealed granular nature of films and no cracks were observed. XPS was employed to study the chemical composition of films. The thin films were studied for their electrical transport behaviour through I-V and Hall measurements. Maximum conductivity of Mg2Si thin films was found to be ∼ 103 S/m and a carrier concentration of 5.14 + 19/cm3 was obtained for 300 nm thick film. The films showed n type nature.

Largely Suppressed Magneto-Thermal Conductivity and Enhanced Magneto-Thermoelectric Properties in PtSn4.

Highly conductive topological semimetals with exotic electronic structures offer fertile ground for the investigation of the electrical and thermal transport behavior of quasiparticles. Here, we find that the layer-structured Dirac semimetal PtSn4 exhibits a largely suppressed thermal conductivity under a magnetic field. At low temperatures, a dramatic decrease in the thermal conductivity of PtSn4 by more than two orders of magnitude is obtained at 9 T. Moreover, PtSn4 shows both strong longitudinal and transverse thermoelectric responses under a magnetic field. Large power factor and Nernst power factor of approximately 80–100 μW·cm−1·K−2 are obtained around 15 K in various magnetic fields. As a result, the thermoelectric figure of merit zT is strongly enhanced by more than 30 times, compared to that without a magnetic field. This work provides a paradigm for the decoupling of the electron and hole transport behavior of highly conductive topological semimetals and is helpful for developing topological semimetals for thermoelectric energy conversion.

Tunable electronic properties and Schottky barrier in a graphene/WSe2 heterostructure under out-of-plane strain and an electric field.

Tuning the electrical transport behavior and reducing the Schottky barrier height of nanoelectronic devices remain a great challenge. To solve this issue, the electronic properties and Schottky barrier of the graphene/WSe2 heterostructure are investigated by the first-principles method under out-of-plane strain and an electric field. Our results show that the WSe2 monolayer and graphene could form a stable van der Waals heterostructure and the intrinsic electronic properties are well preserved. Furthermore, a transformation of a Schottky contact from the n-type to p-type occurs at d = 3.87 Å and E = +0.06 V Å-1. In addition, an ohmic contact is formed with E = -0.50, ±0.60 V Å-1. Lastly, the effective masses of electrons and holes are calculated to be 0.057m0 and -0.055m0 at the equilibrium state, respectively, indicating that the heterostructure has a high carrier mobility. Our research will provide promising approaches for the future design and development of graphene/WSe2 nano-field effect transistors.

Anomalous low temperature electrical transport behaviour of Nd0.7Sr0.3MnO3 thin films: presence of localized magnetic moments

In this work, a detailed investigation of low temperature electrical transport behaviour of Nd0.7Sr0.3MnO3 thin films grown on (001) oriented LaAlO3 substrate by RF magnetron sputtering is reported. Temperature (T) dependence of electrical resistivity [ρ(T)] exhibits metal—insulator transition (TMI) with low temperature minima (Tmin) and further increase in resistivity with decrease in temperature. At T < Tmin, ρ(T) is well agreed with logarithmic temperature relation i.e. with spin state (S) of 3/2 and Kondo temperature (TK) of ∼10 K, but the contribution of logarithmic temperature is suppressed by employing a magnetic field of 5 T. This behaviour of ρ(T) resembles Kondo like spin disorder scattering in the absence of magnetic field and in the presence of magnetic field, the feature of ρ(T) is appeared due to the localized states of electrons in a weakly potentials. Negative magneto-resistivity (MR) of the films signifies that the electron—electron interaction is more dominated under the magnetic field. T > Tmin, ρ(T) in the metallic region is demonstrated by the electron—phonon interaction (T5). Maximum MR is found to be 96% in the magnetic field of 5 T for small thickness film.