Low-temperature Electrical Conductivity Research Articles

Low-Temperature Electrical Conductivity in Mn-Doped Bi0.9Sb0.1 Solid Solutions

Low-Temperature Electrical Conductivity in Mn-Doped Bi0.9Sb0.1 Solid Solutions

Low-temperature resistant self-healing hydrogel electrolyte for dendrite-free flexible zinc-ion hybrid supercapacitors

Flexible zinc-ion hybrid supercapacitors (ZHSC), have great potential as a novel energy storage device, and the appropriate electrolyte with stable low-temperature resistance and high conductivity is crucial for its widespread practical application. Herein, a poly (vinyl alcohol) (PVA)- carboxymethylcellulose sodium salt (CMC) hydrogel electrolyte is prepared by the repeated freezing method, with the advantages of low-temperature resistance, high conductivity, excellent mechanical properties (stretching, compression and torsion), and a certain degree of self-healing function to resist the damage of tearing. The PVA main chain in the gel forms a semi-interpenetrating network with CMC, which improves the mechanical strength of the gel, as well as enhances the binding ability with Zn2+ and promotes the uniform distribution of Zn2+. The incorporation of Li+ into the polymer network disrupts the crystalline domains, enhancing the viscosity and self-healing properties of the gel while improving its low-temperature resistance and electrical conductivity. The conductivity of the gel at 25/-20 °C is 5.17/2.37 mS cm−1. In addition, ethylene glycol (EG) is added to the gel as an antifreeze agent to help the gel not freeze easily at low temperatures. A low-temperature flexible ZHSC are prepared using PVA-CMC/Zn(CF3SO3)2/Li+/EG hydrogel electrolytes and carbonized ZIF-8 (HC) as the electrode. When at a current density of 2 mA cm−2, the device exhibits a specific capacitance of 282.7 mF cm−2 (141.4 F g−1) at room temperature, 270.4 mF cm−2 (135.2 F g−1) at −20 °C and even 61.7 mF cm−2 (135.2 F g-1) at −30 °C. Furthermore, the hydrogel electrolyte can efficiently inhibit the growth of zinc anode dendrites, thus guarantee the good capacitance retention of 81.7 % at 25 °C for 10,000 cycles and a coulombic efficiency of approximately 100 %. The device is also electrochemically stable under various bending conditions, and can power the timer at −30 °C, demonstrating new possibilities for the low-temperature flexible ZHSC.

Low-temperature electrical conductivity of ion-beam irradiated Bi–Sb films

Bismuth-antimony alloys are among the most studied topological insulators and also have very promising thermoelectric properties. In addition, in the amorphous state they exhibit superconductivity with critical temperatures in the range 6.0–6.4 K. In this work, we have prepared and studied different polycrystalline films of Bi100–xSbx (x = 0, 5, 10, 15), and we have induced, through ion beam irradiation, significant damage in their internal structure with the aim of amorphizing the material. Specifically, we have irradiated Bi ions in the 10–30 MeV range, exploiting the capabilities of a 5 MV ion beam accelerator of tandem type. We have characterized the Bi–Sb films before and after irradiation from a morphological and structural point of view and measured their electrical resistivity from room temperature to near 2 K, to evaluate the influence of the preparation method and degree of disorder. We have found that the studied Bi–Sb system always behaves as a small energy gap semiconductor that follows the empirical Meyer–Neldel rule, which correlates the conductivity prefactor with the exponential value of the energy gap.

Liquid metal droplets bouncing higher on thicker water layer

Liquid metal (LM) has gained increasing attention for a wide range of applications, such as flexible electronics, soft robots, and chip cooling devices, owing to its low melting temperature, good flexibility, and high electrical and thermal conductivity. In ambient conditions, LM is susceptible to the coverage of a thin oxide layer, resulting in unwanted adhesion with underlying substrates that undercuts its originally high mobility. Here, we discover an unusual phenomenon characterized by the complete rebound of LM droplets from the water layer with negligible adhesion. More counterintuitively, the restitution coefficient, defined as the ratio between the droplet velocities after and before impact, increases with water layer thickness. We reveal that the complete rebound of LM droplets originates from the trapping of a thinly low-viscosity water lubrication film that prevents droplet-solid contact with low viscous dissipation, and the restitution coefficient is modulated by the negative capillary pressure in the lubrication film as a result of the spontaneous spreading of water on the LM droplet. Our findings advance the fundamental understanding of complex fluids’ droplet dynamics and provide insights for fluid control.

Robust metal-insulator transition in "112″-layered double perovskites Y1−xLnxBaCo2O5.50±δ (Ln = Sm, Eu and Gd; x = 0, 0.5 and 1)

We report the synthesis, structural, magnetic, electrical transport, magnetoelectric and thermoelectric properties of ″112″-layered double perovskite Y1−xLnxCo2O5.5 (Ln = Sm, Eu and Gd; x = 0, 0.5 and 1) cobaltites. YBaCo2O5.50 exhibits simultaneous structural, magnetic and electrical transitions around 300 K. Whereas LnBaCo2O5.50 (Ln = Sm, Eu and Gd) exhibit well separated TC and TIM, respectively, below and above 300 K. It is expected from the chemical viewpoint that the substitution of Ln by Y in LnBaCo2O5.50 should result in proximity of TC and TIM. However, our investigation demonstrates that though TC shows significant upward shift, TIM exhibits robustness. This suggests that the electrical and magnetic transitions are decoupled. The large MR [(ρH-ρ0)/ρ0] values (~50%) at low temperatures are observed for Eu and Gd-phases. The low temperature electrical conduction mechanism is of variable range hopping (VRH) type and the thermoelectric properties suggest the p-type polaronic conductivity or hole like carriers in the samples. The observed results can be understood in the framework of electronic phase separation and the metal-insulator transition from viewpoint of structural transition instead of the spin state transition.

Electronic structure and transport property of p-type Mg3Sb2 from first-principles study

Numerous efforts have been paid on n-type Mg3Sb2-based Zintl compounds with exceptional thermoelectric performance, but seldom on p-type sample with poor electrical transports. In this work, we investigate the electronic structure and transport properties of p-type Mg3Sb2 by using first-principles method and Boltzmann transport theory. Firstly, the slightly higher low-temperature electrical conductivity for theoretical calculations than experimental results suggest that different from n-type sample, the contribution of eliminating grain boundary scattering to electrical transports is weak in p-type Mg3Sb2. Secondly, the calculated higher Seebeck coefficient along x-axis and higher electrical conductivity along z-axis reveal the anisotropy of electrical transports, and this phenomenon may be ascribed to the anisotropic carrier's effective masses. Because the gradual leading role of Seebeck coefficient as temperature increasing, the peak power factor along x-axis exceeds that along z-axis at temperature above ∼500 K, which indicates that further improvement of the electrical performance can be expected through anisotropic transports. Thirdly, the effect of the adsorption of oxygen atom on Mg3Sb2 (001) surface on the electronic structure are investigated. This work aims to provide new insight into the optimization of p-type electrical transport property, thereby closing the gap with n-type property for developing Mg3Sb2-based thermoelectric devices.

Low temperature electrical conduction mechanisms in disordered materials with an application to Calcium Strontium Copper Titanate ceramics

Hopping conduction mechanism is studied in Strontium doped Calcium Copper Titanate (CSCTO) ceramics at low temperatures down to 93 K. The method of analyzing the local activation energy is used to identify the variable range hopping (VRH) nature in these ceramics. The frequency dependence of the corresponding localization length of mobile charge carriers is discussed. The electrical conductivity analysis in frequency up to 1 MHz suggests the predominance of the overlapping large polaron tunneling (OLPT) mechanism. The data are analyzed in light of existing theoretical models of VRH and OLPT.

Low-temperature electrical conductivity of composite film formed by carbon nanotubes with MoS2 flakes

Multifunctional composite nanosystems containing both one-dimensional and two-dimensional nanostructures possess improved electrical, mechanical, and thermal properties which offer a wide range of applications. In this work, the composite films formed by single-walled carbon nanotubes and MoS2 flakes (MoS2-SWNTs) are studied exploiting Raman spectroscopy, scanning electron microscopy, and low-temperature conductivity measurements (5–312 K). The MoS2-SWNTs and SWNTs films demonstrate the semiconductor behavior with negative temperature coefficient of resistance. The temperature dependence of the composite film resistance in the range of 5–204 K is considered whithin the framework of Mott model that describes the motion of electrons with variable range hopping due to thermally activated tunneling (3D Mott VRH model). At T > 204 K, the temperature dependence of composite film resistance was fitted by the Arrhenius-like equation. The empirical parameters included in two transport models were evaluated. The comparison between the composite and SWNTs films shows that the conductivity of the composite is mostly determined by nanotubes.

Effect of the substrate on the electrical transport and fluctuation processes in NbRe and NbReN ultrathin films for superconducting electronics applications

NbRe-based superconducting thin films recently received relevant interest in the field of low-temperature electronics. However, for these materials the electrical conduction mechanisms, in particular in the normal state, still need to be investigated in more detail. Here, NbRe and NbReN films of different thicknesses have been deposited on two different substrates, namely monocrystalline Si and text {SiO}_2 buffered Si. The films were characterized by DC electrical transport measurements. Moreover, a connection with the charge carriers fluctuation processes has been made by analyzing the electrical noise generated in the normal state region. Despite the films morphology seems not to be affected by the substrate used, a lower noise level has been found for the ones grown on text {SiO}_2, in particular for NbReN. From this study it emerges that both NbRe and NbReN ultrathin films are of very good quality, as far as the low-temperature electrical noise and conduction are concerned, with noise levels competitive with NbN. These results may further support the proposal of using these materials in a nanowire form in the field of superconducting electronics.

Studies of Anomalies in Mixed Conduction of Na<sub>2</sub>O and V<sub>2</sub>O<sub>5</sub> Doped Boro-Phosphate Glasses

A set of borophosphate glasses doped with alkali and transition metal (TM) ions have been synthesized. The glasses were carried through; annealing, XRD, density, DC conductivity studies. Molar volume and density varied nonlinearly. High temperature activation energy is analysed taking into consideration of Mott’s SPH model. The low temperature electrical conductivity was analysed by Mott and Greaves VRH. Several polaron hopping related parameters at high temperature region and density of states at low temperature region were computed. The high temperature DC activation energy measured by conductivity, calculated numerous pertained parameters varied nonlinearly with mole fraction of vanadium content. The Study exhibits DC electrical conduction is due to both alkali and transition metal ions and thus confirms the mixed conductivity. A crossover conduction mechanism from the ionic dominant region to polaronic predominant region has been also observed. Studies revealed the single transition effect at 0.4 mol fraction of V2O5 content.

Flexibility of Room-Temperature-Synthesized Amorphous CdO-In2O3 Alloy Films and Their Application as Transparent Conductors in Solar Cells.

Due to their low-temperature deposition, high mobility (>10 cm2/V·s), and electrical conductivity, amorphous ionic oxide semiconductors (AIOSs) have received much attention for their applications in flexible and/or organic electro-optical devices. Here, we report on a study of the flexibility of CdO-In2O3 alloy thin films, deposited on a polyethylene terephthalate (PET) substrate by radio frequency magnetron sputtering at room temperature. Cd1-xInxO1+δ alloys with the composition of x > 0.6 are amorphous, exhibiting a high electron mobility of 40-50 cm2/V·s, a low resistivity of ∼3 × 10-4 Ω·cm, and high transmittance over a wide spectral window of 350 to >1600 nm. The flexibility of both crystalline and amorphous Cd1-xInxO1+δ films on the PET substrate was investigated by measuring their electrical resistivity after both compressive and tensile bending with a range of bending radii and repeated bending cycles. Under both compressive and tensile bending with Rb = 16.5 mm, no significant degradation was observed for both the crystalline and amorphous films up to 300 bending cycles. For a smaller bending radius, the amorphous film shows much less electrical degradation than the crystalline films under compressive bending due to less film delamination at the bending sites. On the other hand, for a small bending radius (<16 mm), both crystalline and amorphous films degrade after repeated tensile bending, most likely due to the development of microcracks in the films. To demonstrate the application of amorphous Cd1-xInxO1+δ alloy in photovoltaics, we fabricated perovskite and bulk-heterojunction organic solar cells (OSCs) on glass and flexible PET utilizing amorphous Cd1-xInxO1+δ layers as transparent electrodes. The organic-inorganic hybrid perovskite solar cells (PSCs) exhibit a power conversion efficiency (PCE) of ∼11 to 12% under both front and back illumination, demonstrating good bifacial performance with bifaciality factor >90%. The OSCs fabricated on an amorphous Cd1-xInxO1+δ-coated flexible PET substrate achieve a promising PCE of 12.06%. Our results strongly suggest the technological potentials of amorphous Cd1-xInxO1+δ as a reliable and effective transparent conducting material for flexible and organic optoelectronic devices.

Dopant-segregation to grain boundaries controls electrical conductivity of n-type NbCo(Pt)Sn half-Heusler alloy mediating thermoelectric performance

Science-driven design of future thermoelectric materials requires a deep understanding of the fundamental relationships between microstructure and transport properties. Grain boundaries in polycrystalline materials influence the thermoelectric performance through the scattering of phonons or the trapping of electrons due to space-charge effects. Yet, the current lack of careful investigations on grain boundary-associated features hinders further optimization of properties. Here, we study n-type NbCo1-xPtxSn half-Heusler alloys, which were synthesized by ball milling and spark plasma sintering (SPS). Post-SPS annealing was performed on one sample, leading to improved low-temperature electrical conductivity. The microstructure of both samples was examined by electron microscopy and atom probe tomography. The grain size increases from ~230 nm to ~2.38 μm upon annealing. Pt is found within grains and at grain boundaries, where it locally reduces the resistivity, as assessed by in situ four-point-probe electrical conductivity measurement. Our work showcases the correlation between microstructure and electrical conductivity, providing opportunities for future microstructural optimization by tuning the chemical composition at grain boundaries.

Low-temperature thermal conductivity of thermoelectric Co1−xMxSi (M = Fe, Ni) alloys

We study the low-temperature electrical and thermal conductivity of CoSi and Co1−xMxSi alloys (M = Fe, Ni; x ≤ 0.06). Measurements show that the low-temperature electrical conductivity of Co1−xFexSi alloys decreases at x > 0.01 by an order of magnitude compared with that of pure CoSi. It was expected that both the lattice and electronic contributions to thermal conductivity would decrease in the alloys. However, our experimental results revealed that at temperatures below 20 K, the thermal conductivity of Fe- and Ni-containing alloys is several times larger than that of pure CoSi. We discuss possible mechanisms of the thermal conductivity enhancement. The most probable one is the dominant scattering of phonons by charge carriers. We propose a simple theoretical model that takes into account the complex semimetallic electronic structure of CoSi with nonequivalent charge carrier pockets. This model explains well the increase of the lattice thermal conductivity with increasing disorder and the linear temperature dependence of thermal conductivity in the Co1−xFexSi alloys below 20 K.

Surface Conductivity of the Ytterbium-Doped Topological Kondo-Insulator SmB6

The temperature dependence of the conductivity of the topological Kondo-insulator (TKI) Sm1 – xYbxB6 is investigated in the temperature range 2 < T < 300 K for compositions with x ≤ 0.024. It is found that the ytterbium impurity most strongly affects the low-temperature (T < 20 K) electrical conductivity: when changing from x = 0 to x = 0.024, the activation energy of bulk conductivity decreases by 1.8 times from 4 to 2.2 meV, and the 2D surface conductivity increases by six times. The separation made for the contributions to the conductivity enables us to establish that the one-parameter scaling model can be used for describing the conductivity of 2D surface states in the Sm1 – xYbxB6 TKI in which both the interaction with phonons and the electron–electron scattering effects are taken into account.

Qualidade fisiológica durante o armazenamento de sementes de algodão repassadas na mesa densimétrica

Objetivou-se com o presente trabalho avaliar a qualidade fisiológica durante o armazenamento das sementes de algodão coletadas em diferentes posições da mesa densimétrica após o seu beneficiamento. Foram utilizadas sementes de algodão (Gossypium hirsutum L. r.) cultivar BRS 269 - Buriti, com teor de água inicial 9,98±0,48% base úmida (b.u.). Inicialmente, as sementes foram beneficiadas e em seguida foram repassadas na mesa densimétrica para separação. Posteriormente, as sementes foram armazenadas em ambiente natural. Os tratamentos foram os pontos de coleta localizados na saída da mesa densimétrica: controle (sementes beneficiadas sem repasse na mesa densimétrica); 0 a 16 cm (A); 16 a 32 cm (B); 32 a 48 cm (C); 48 a 64 cm (D); 64 a 80 cm (E) e 80 a 96 cm (F) e o tempo de armazenamento (0, 60, 120 e 180 dias). Foram avaliados ao longo do armazenamento o teor de água, massa específica aparente, germinação, índice de velocidade de germinação (IVG), germinação a baixa temperatura e condutividade elétrica. O teor de água e a massa específica aparente apresentaram variações durante o armazenamento. A germinação em baixa temperatura reduziu enquanto a condutividade elétrica aumentou para todos os tratamentos indicando uma perda de qualidade ao longo do armazenamento, sendo estes comportamentos foram de menor intensidade para o tratamento A e de maior intensidade para o tratamento F. O descarte das sementes da parte mais baixa (Tratamento F) da mesa densimétrica durante o repasse contribui para a melhoria da qualidade fisiológica dos lotes de sementes de algodão.

The effect of structure on the low-temperature electrical conductivity of carbon nanocomposite temperature sensors

The electrical conductivity of carbon nanocomposite TVO-series resistors used as temperature sensors are studied in a wide temperature range of 300–1.8 K. It is found that hopping conductivity emerges at temperatures below 77 K. The shape of its temperature dependence varies for resistors having different resistance at room temperature. Raman spectra measurements have shown that the resistors differ according to the size of the carbon nanoparticles in the composite material of the conducting region and its dispersion along the direction of the current. The measured dependences of conductivity on temperature and magnitude of the applied electric field, wherein the charge carriers are heated by the field, are used to determine charge carrier localization lengths, which are almost two orders of magnitude greater than the carbon nanoparticles. The observed features of the conductivity can be explained by a nonuniform distribution of carbon in the composite material and the formation of nanoparticle clusters with quasi-metallic conductivity, while the conductivity between the clusters occurs due to carrier hopping.

Effect of grain size on low-temperature electrical resistivity and thermal conductivity of pure magnesium

The electrical resistivity and thermal conductivity of as-cast pure Mg with different grain sizes prepared by ultrasonic treatment were measured in the temperature range of 2–320 K. The grain size has little effect on residual electrical resistivity, but the different samples exhibit different temperature coefficients of resistance. The maximum of thermal conductivity 665 W/(m·K) appears at ∼20 K where the different grain sizes shows the biggest difference. Less effect of grain size on the thermal conductivity can be observed at room temperature.

Low-temperature electrical conduction of plasma-treated bilayer MoS2

Abstract

Raman spectroscopy and low temperature electrical conductivity study of thermally evaporated CdS thin films

A systematic study has been carried out on properties of CdS thin films grown on glass substrates by thermal route and growth parameters have been optimized to achieve near stoichiometry. Raman spectroscopy of the films has been carried out to get more insight on chemical and structural information of the films. Photoluminescence study was carried out to get the knowledge of defect-states which play major role in transport mechanisms. In order to obtain electrical parameters, Hall measurement has been carried out by van der Pauw’s technique at room temperature. Also, variation of electrical resistivity of the films at temperature range 20–300 K has been studied. Finally effect of post deposition annealing on the structural, optical and electrical properties of these films has been studied.

Strongly Correlated Metal Built from Sachdev-Ye-Kitaev Models.

Prominent systems like the high-T_{c} cuprates and heavy fermions display intriguing features going beyond the quasiparticle description. The Sachdev-Ye-Kitaev (SYK) model describes a (0+1)D quantum cluster with random all-to-all four-fermion interactions among N fermion modes which becomes exactly solvable as N→∞, exhibiting a zero-dimensional non-Fermi-liquid with emergent conformal symmetry and complete absence of quasiparticles. Here we study a lattice of complex-fermion SYK dots with random intersite quadratic hopping. Combining the imaginary time path integral with real time path integral formulation, we obtain a heavy Fermi liquid to incoherent metal crossover in full detail, including thermodynamics, low temperature Landau quasiparticle interactions, and both electrical and thermal conductivity at all scales. We find linear in temperature resistivity in the incoherent regime, and a Lorentz ratio L≡(κρ/T) varies between two universal values as a function of temperature. Our work exemplifies an analytically controlled study of a strongly correlated metal.