Dependence Of Resistance Research Articles

Exploration of electrical conduction mechanisms via modulating sintering period of La0.67Ca0.33MnO3 films in various phase regions

Perovskite manganese oxide films have garnered significant attention due to their unique and diverse physical properties. In this work, La0.67Ca0.33MnO3 (LCMO) films are prepared on LaAlO3 (00l) substrates using the sol−gel spin coating method with varying sintering period (Ps). By optimizing Ps, improvements were observed in the films’ structure, morphology, ionic valence, and temperature−dependent resistivity. The reduction in Mn−O bond length and the increase in Mn−O−Mn bond angle change the degree of MnO6 distortion, resulting in an increased eg bandwidth. As Ps increased, the LCMO films exhibited better crystalline quality. The improved Mn4+/Mn3+ ratio strengthened the double exchange effect, facilitating the carrier hopping of the eg electrons. Analyses of various electrical conduction mechanisms showed that optimized electron scattering behavior, reduced hopping distance, energy and theoretical Curie temperature collectively enhance the temperature coefficient of resistivity (TCR) of LCMO films under optimal Ps. The TCR of the LCMO films reached a maximum value (31.64 % K−1) at Ps = 18 min. These findings offer valuable insights into the main electrical conduction mechanisms in both metallic and semiconducting phases, providing a deeper understanding of the underlying physical processes and offering experimental guidance for optimizing the electrical transport properties of perovskite films.

Role of divalent doping at A-sites (A=Ca2+, Sr2+, Ba2+ & Pb2+) on thermoelectric and magnetoresistive properties in La0.67(Bi0.0835Na0.0835) A0.165MnO3

The present work reports on the effect of divalent ion doping (Ca2+, Sr2+, Pb2+ & Ba2+) ions at A-site in the compound with compositional formula La0.67(Bi0.0835Na0.0835)A0.165MnO3 on structural, magnetic, magneto-transport and thermoelectric properties. X-ray diffraction reveals orthorhombic structure for calcium and barium doped with no peak splitting observed at ~ 32o whereas rhombohedral structure for strontium and lead dopants with a peak splitting in the main intensity. Doping with divalent ions at A-site in La0.67(Bi0.0835Na0.0835)A0.165MnO3 manganites has introduced Mn2+ ions, changing the ratio of Mn3+/Mn4+ in octahedral site and this has been confirmed from X-ray photospectroscopy studies. The field emission scanning electron microscope images confirm different grain sizes and morphologies for different doping elements and distinguished variation is noticed for strontium doped manganites with a grain size of 1.08µm. Room temperature ferromagnetic behavior was observed in the samples at room temperature except for calcium doped sample and magnetic behavior has been discussed on the basis of the various interactions between mixed valence manganese ions and Mn3+/Mn4+ ratio. Electrical resistivity (ρ) as a function of temperature (T) without magnetic field indicates the double peak behavior and with the application of external magnetic fields, the double peak disappears, in all the investigated samples. Highest MR% at their respective transition temperatures (TP1) has been obtained for lead doped samples when compared to barium, strontium and calcium samples. Activation energies (EP) estimated decreases initially for calcium and strontium whereas it increases for lead and barium dopants i.e. for further increases in ionic radii. The change of sign from positive to negative in Seebeck coefficient (S) was noticed with increasing ionic radii suggesting the variation in the nature of charge carriers. The electron-electron, electron-magnon, magnon-magnon scattering mechanism contributes to the temperature dependent resistivity and thermopower in the low temperature region while in the paramagnetic insulating region is governed by a small polaron hopping mechanism.

2D versus 3D-Like Electrical Behavior of MXene Thin Films: Insights from Weak Localization in the Role of Thickness, Interflake Coupling and Defects.

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti3C2Tx. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti3C2Tx thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti3C2Tx thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length lϕ, estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than lϕ, hence acting as parallel 2D conductors. Alternatively, lϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thinfilms.

Giant and negative magnetoresistances in conical magnets in the nonequilibrium Boltzmann equation approach

We study magnetotransport in conical helimagnet crystals using the nonequilibriun Boltzmann equation approach. Spin dependent magnetoresistance exhibits dramatic properties for high and low electron concentrations at different temperatures. For spin up electrons we find negative magnetoresistance despite only considering a single carrier type. For spin down electrons we observe giant magnetoresistance due to depletion of spin down electrons with an applied magnetic field. For spin up carriers, the magnetoresistance is negative, due to the increase in charge carriers with a magnetic field. In addition, we investigate the spin dependent Hall effect. If a magnetic field reaches some critical value for spin down electrons, giant Hall resistance occurs, i.e. Hall current vanishes. This effect is explained by the absence of spin down carriers. For spin up carriers, the Hall constant dramatically decreases with field, due to the increase in spin up electron density. Because of the giant spin dependent magnetoresistance and Hall resistivity, conical helimagnets could be useful in spin switching devices.

Improving of thermoelectric figure of merit in Sr0.925Dy0.075TiO3 ceramics

Rare earth doped SrTiO3 is one of the most promising oxide materials meeting the safety and stability requirements for potential applications in thermoelectric converters. This work aims to assess the feasibility of engineering SrTiO3-based materials to improve their thermoelectric performance. A comparative analysis of the thermoelectric properties of Sr0.925Dy0.075TiO3 ceramic samples obtained from preliminarily mechanically activated Sr0.925Dy0.075TiO3 nano-powder by two methods – solid-state reaction synthesis and spark plasma sintering – was carried out. Significant differences in the morphology of the samples lead to significant differences in the temperature dependences of electrical resistivity and the Seebeck coefficient. Ceramics obtained by solid-state reaction synthesis exhibit lower porosity and lower electrical resistivity. The thermoelectric power factor of such ceramics is 2–3 times higher than that of samples obtained by spark plasma sintering. The obtained value of thermoelectric figure of merit ZT = 0.41 at T = 673 K for Sr0.925Dy0.075TiO3 is the highest value among n-type oxide thermoelectric ceramics at a given temperature and maintains a tendency to increase with increasing temperature.

Influence of trapped magnetic field of Sn-Pb solders on electrical resistivity measurement: an example of superconducting transition of Sn

We examined the effect of the flux-trapped states of Sn60-Pb40 solders on the superconducting properties of a Sn wire. The temperature dependence of electrical resistivity at H = 0 Oe after zero-field cooling (ZFC) showed a sharp superconducting transition at T = 3.7 K. In contrast, field cooling (FC) resulted in a broadening of the transition. The difference between ZFC and FC data evidences the critical effect of trapped fluxes at solders on superconducting states. We propose that, in electrical measurements where magnetic fields of several hundred Oe are critical, field experience should be seriously considered when using solders.

Rate-dependent mechanical and self-monitoring behaviors of 3D printed continuous carbon fiber composites

3D printed continuous carbon fiber reinforced polymer (CFRP) composites offer great advantages in structural health monitoring (SHM) owing to their flexibility in complex structure fabrication. Considering the many prospective aerospace applications, tensile experiments were designed to study their mechanical and self-sensing behaviors under a wide range of strain rates. The turning points in the resistance vs strain curves reveal the damage evolution of the specimens and divide the deformations into linear straining and damage evolution regions. Fiber elongation and fiber contact reduction dominate the resistance increase in the linear straining region and the resistance curve behaves linearly. But fiber breakage is the predominant factor in the damage evolution region, yielding a concave resistance curve. Strength, fracture strain, and resistance variation are found to display significant strain rate dependencies that increase with increasing strain rate. Numerous microcracks are formed and evolved into secondary cracks under dynamic loading. This process absorbs more strain energy and produces more carbon fiber breaks, sustaining a higher fracture strain and resistance variations. A model is developed to describe the strain- and strain rate- dependent resistance behaviors, and the predicted results agree well with experimental data. The outcomes of this work contribute to the application of 3D printed continuous CFRP composites in SHM.

Size dependence of electrical resistivity caused by stress-induced rejuvenation for metallic glassy microfibers

In this paper, we investigate the electrical transport properties of Zr-, La- and Pd-based metallic glassy fibers (MGFs) with diameters at microscale, which are fabricated by superplastic deformation at high temperatures. It is found that with the decrease of the diameter, the resistivity of the MGF increases with decreasing temperature more quickly. As compared to the thicker one, the structure of the thinner MGF is more strongly rejuvenated with a larger relaxation enthalpy, a larger average short-range atomic distance and less crystal-like structure induced by the larger normal stress during its formation process. Based on the evolution of the heterogeneous structure, the dependence of electrical resistivity on the size for the MGFs is interpreted within the extended Ziman liquid-metal theory. The results might be significant for controlling the electrical properties of MGFs via tunning their glassy states and applying them in micro-electromechanical systems.

Prediction of the residual lifetime of bitumen coatings on urban gas pipelines from the change in their mechanical characteristics during thermal-oxidative aging

Residual life of bitumen insulation is an important parameter of urban gas pipelines. Its fast and reliable estimation is necessary for timely health monitoring and coating restoration. In this study, we propose to define lifespan of bitumen insulation in situ from the mechanical characteristics measured during its thermal-oxidative aging. For evaluation of elastic and viscous properties, micro-impact dynamic indentation was applied. We determined the values of activation energy under thermal destruction and the dependence of transient electrical resistance on the critical values of coating's mechanical properties. Obtained experimental data foster real-time estimation of service time of insulation without coating removal.

Low temperature dependence of electrical resistivity in obliquely sputter-deposited transition metal thin films

Transition metals exhibiting hcp (Ti, Zr, Hf) and bcc (V, Nb, Ta, Cr, Mo, W) crystalline structures are DC sputter-deposited by oblique angle deposition. A constant film thickness of 400 nm is prepared, whereas the deposition angle α is systematically changed from 0 to 85° A columnar structure is produced with column angle reaching β = 50° for the highest deposition angle. Crystallinity and grain size are both reduced with an increasing deposition angle, especially for α higher than 60° DC electrical resistivity vs. temperature in the range 7–300 K shows a typical metallic-like behavior with films becoming more resistive for high deposition angles. For temperatures higher than 100 K, the linear temperature dependence of resistivity is obtained for films prepared with deposition angles lower than 60° The electron-phonon is the main interaction acting on electronic transport mechanism. Oblique deposition angles give rise to an enhancement of electron-phonon interactions with a saturation effect of electrical resistivity for some metals. Resistivity measurements at low temperatures (down to 7 K) show the predominance of electron-defect interactions. Electron-phonon-defect interaction effect is particularly investigated as a function of the deposition angle and a shift of the crossover temperature is brought to the fore.

Superconducting thin films of [formula omitted][formula omitted][formula omitted][formula omitted] with zero-resistance transition temperature close to 100 K

High superconducting transition temperature is favorable for the applications of superconductors. Some cuprate superconductors have the transition temperatures above 100 K, such as the Hg- or Tl-based 1223 and 1234 phases, but many of them contain the toxic elements, like Hg and Tl. Meanwhile, the anisotropy of upper critical field or the effective mass of above mentioned Hg-, Tl-based systems, or the non-toxic Bi2Sr2Ca2Cu3O10 with Tc = 110 K is high, which makes the vortices easy to move and the irreversibility magnetic field is very low in the liquid nitrogen temperature region. Here we report the successful synthesis of the c-axis oriented (Cu,C)Ba2Ca2Cu3O9±δ superconducting thin film with the zero-resistance transition temperature reaching 99.7 K. The superconducting transitions are rather sharp as revealed by both resistivity and magnetization measurements. Temperature dependent resistivity has been measured under different magnetic fields, and the irreversibility lines have been achieved. The resistivity was also measured with the magnetic field rotated in the ac-plane, and the data can be nicely scaled by using the anisotropic Ginzburg-Landau model, yielding a temperature dependent anisotropy which varies from 17 at 110 K to 4 at 77 K. Additionally, the critical current density calculated from the magnetization-hysteresis-loops reaches about 6×105A/cm2 (zero field) at 77 K. Thus the film may be a good candidate for the applications of superconducting cables or high frequency superconducting filters in liquid nitrogen temperature region.

Unconventional angular dependence of spin-orbit torque-induced harmonic Hall resistance in Pt/YIG bilayers

Spin-orbit torque (SOT), arising from spin-orbit coupling-induced spin currents, provides efficient control of magnetization. SOT characterization involving harmonic Hall resistances is typically done in low-current regimes, distinct from high-current regimes, where SOT-induced magnetization switching occurs. In this study, we investigate azimuthal angle (ϕ)-dependent harmonic Hall resistances of a Pt/yttrium iron garnet (YIG) layer across a wide range of measurement currents. Under low-current conditions, conventional ϕ-dependent Hall resistances are observed; the first harmonic Hall resistance exhibits sin 2ϕ behavior and the second harmonic Hall resistance comprises cos ϕ and cos 3ϕ terms. Interestingly, with increasing current, higher-order angular-dependent terms become non-negligible, referring to the sin 4ϕ and sin 6ϕ terms for the first harmonic and the cos 5ϕ and cos 7ϕ terms for the second harmonic Hall resistances. We attribute this unconventional angular dependence to the nonlinear response of magnetization direction to SOT, emphasizing its relevance to understanding the magnetization dynamics during SOT-induced switching under large currents.

Insights into existing and futuristic treatment approach for chronic myeloid leukaemia.

Oncogenes play a crucial part in human cancer development, and when particular drugs obstruct the proteins produced by these oncogenes, the tumoural process can be ceased. For instance, in chronic myeloid leukaemia (CML), all pathological traits are associated with a single oncogene, BCR-ABL1. CML is a triphasic cancerous disorder of haematopoietic stem cells, marked by a balanced translocation between chromosomes 9 and 22, leading to the genesis of a Philadelphia chromosome encompassing the BCR-ABL1 fusion gene. This fusion oncogene further produces a constitutive active tyrosine kinase protein, enhancing the downstream signalling pathways and constitutes cancer. The treatment for CML has been entirely altered from chemotherapy and immunotherapy to targeted therapy with the emergence of tyrosine kinase inhibitors (TKIs) which inhibit BCR-ABL1 kinase activity. However, the inhibitory mechanism of TKIs is constrained by BCR-ABL1 dependent and independent resistance mechanisms, prompting the exploration of novel therapeutics through extensive clinical trials to develop next-generation drugs with enhanced potency. The persistent challenges posed by CML have motivated researchers to seek innovative strategies for its eradication, such as the application of the genome editing tool CRISPR/Cas9. This review provides insights into existing CML diagnoses, treatment modalities, resistance mechanisms, drugs under trial phases and new potential therapeutic drugs. Furthermore, the review looks ahead to a visionary perspective wherein the CRISPR/Cas9 approach holds the potential to evolve into a prospective curative measure for CML.

Effect of A-site disorder and reduced grain size on low temperature resistivity minima and magnetoresistance behaviour in Nd0.7-xGdxSr0.3MnO3 (0 ≤ x ≤ 0.3)

ABSTRACT The present work provides a detailed investigation of the electronic- and magneto-transport properties of bulk and nanostructured Nd0.7-xGdxSr0.3MnO3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline manganites. We have specially addressed the issue of the observed minimum in the temperature dependent resistivity of these manganites in the low temperature regime (<50 K). It is observed that increase of A-site disorder due to progressive substitution of Gd and decrease of grain size enhances the observed resistivity minima. Different theoretical models have been employed to analyze the resistivity data in the low temperature regime. It has been established that the quantum interference effect due to electron–electron interaction, most likely, is the dominant factor of the observed resistivity minimum and upturn in resistivity in the lower temperature regime. The effect of phase separation is also found to play a key role in the electronic-transport of the materials. Further the magnetoresistance is found to increase with the increase of Gd concentration as well as with the decrease of grain size in the low temperature regime. The origin of magnetoresistance has been critically analyzed.

Temperature dependent electrical resistance and mesoscopic electronic transport mechanisms on aerographite and single-walled carbon nanotube aerogel

We investigate temperature dependent electrical resistance properties of aerographite and single-walled carbon nanotube (SWCNT) aerogel in the temperature range of 2–300 K by employing the four-probe method with magnetic field effects (in the range 0–9 T, in steps of 2 T). The current–voltage (I–V) curves were taken for several temperatures varying from 5 to 300 K, and the electrical resistance values of aerographite and SWCNT aerogel were decreased from 7.30 Ω (5 K, 0 T) to 4.88 Ω (300 K, 0 T) and 22.56 Ω (5 K, 0 T) to 0.99 Ω (300 K, 0 T) with temperature increases, respectively. Experimental results show that the electrical resistance falls exponentially as the temperature increases. Such temperature dependence of R(T) points to a form of tunneling conduction or hopping. Two mesoscopic mechanisms for electronic transport, fluctuation-induced tunneling conduction (FITC) and variable range hopping (VRH), are employed to explicate possible electrical conduction mechanisms occurring in aerographite and SWCNT aerogel, respectively. These mainly result in disorder-induced symmetry-breaking, which are modified by their structural symmetries and electronic band structures, both play important roles in temperature dependent electrical resistance properties of aerographite and SWCNT aerogel. Characteristic parameters (T0, T1, and R0) have been estimated using the morphology and the uncertainty principle for aerographite and the percolation theory for SWCNT aerogel. While the FITC mechanism captures a wide temperature range of data for aerographite, the VRH model provides an explanation for SWCNT aerogel. This study provides groundwork for further development of carbon aerogel systems with high conductivity in large-scale preparation.

Light Dependent Negative Differential Resistance and Resistive Switching in Oxide Semiconductors

Light Dependent Negative Differential Resistance and Resistive Switching in Oxide Semiconductors

ABa6Cu31Te22 (A = K, Rb, Cs) Featuring Polyanionic Copper-Telluride Frameworks with Ultralow Thermal Conductivity.

Three polyanionic tellurides, ABa6Cu31Te22 (A = K, Rb, Cs), were synthesized in salt flux. The isostructural tellurides crystallize in a new structure type, in the cubic Pa3 space group with a Wyckoff sequence of d10c2b1 and large unit cell volumes of over 5500 Å3. The structures feature a framework of [CuTe4] tetrahedra and [CuTe3] trigonal pyramids with disorder in the Cu sites. The polyanionic frameworks have large square antiprism and cuboctahedral voids where Ba and alkali metal cations are situated, forming [BaTe8] and [ATe12], respectively. The overall compositions are close to being charge balanced. The large [ATe12] cuboctahedra allowed for significant anisotropic displacement of the A cations, as observed from both single crystal X-ray diffraction and heat capacity studies. Alkali cations rattling together with Cu atom displacement and disorder leads to the dispersion of phonons, thus softening the lattice and subsequently reducing the thermal conductivity. Evaluations of the electronic band structure revealed the occurrence of a narrow bandgap together with the presence of a flat band near the valence band maximum, giving rise to the high thermopower. The Cs and Rb analogues show a slope change in the temperature dependence of electrical resistivity around room temperature, which is typical for semimetals or degenerate semiconductors. For the as-synthesized and unoptimized materials, high values of the thermoelectric figure-of-merit of ∼0.2 were observed at 623 K.

Strain and orientation modulated optoelectronic properties of La-doped SrSnO3 epitaxial films

We have studied the structural, electrical, and optical properties of La0.05Sr0.95SnO3 thin films, which exhibited a strong dependence upon the substrate’s orientation and strain. X-ray diffraction results show that the LSSO films grow epitaxially on (001) and (011)-oriented LaAlO3 substrates, and the in-plane compressive strain decreases gradually upon increasing film thickness. Room-temperature resistivity varies from 4.23 (13.0) to 1.37 (4.76) mΩ cm as the film thickness increases for (001) orientation ((011) orientation). Temperature dependent resistivity curves of all the samples show a metal–semiconductor transition (MST), which can be explained by the electron–electron interactions below MST rather than weak localization. Both reducing the in-plane compressive strain and transferring the orientation from (011) to (001) can drive the MST point shifts toward lower temperature, indicative of the enhancement of the metallic transport in the films. The band gap increases upon increasing film thickness due to Burstein-Moss effect. The charge distributions of Sn and O from density functional theory (DFT) calculations illustrate that (001)-plane has a better conductivity. Furthermore, our DFT results also demonstrate that decreasing the in-plane strain will lead to a smaller electron effective mass, thus the increased carrier mobility can be obtained. These comprehensive investigations advance our knowledge of the optoelectronic characteristics and provide valuable insights for future research in related transparent materials.

Structural, magnetic, magnetocaloric behavior and magneto-transport, electrical polarization study in 3d based bulk and nano-crystalline multiferroic double perovskite Dy2MnCoO6

In this paper, we report a detailed investigation of the crystal structure, magnetic, magnetocaloric, magneto-transport and electrical polarization properties of a new multiferroic material in the polycrystalline and nanocrystalline form of the Dy2MnCoO6 double perovskite. Both compounds crystallized in the monoclinic structure with P21/n space group. The magnetic properties of both systems are mainly dominant ferromagnetic (FM) and weak antiferromagnetic (AFM). The FM/AFM coupling is related by the competing and combining functions of the radius and the magnetic moments of rare earth ions (i.e. 3d–4f exchange interactions). The reduction of the saturation magnetization in the isothermal magnetization curves can be explained by the existence of anti-phase boundaries and local anti-site defects in the system. Moreover, these materials hold reasonable values of magnetocaloric parameters and the absence of hysteresis makes the system a potential candidate for magnetic refrigeration. These compounds revealed two magnetic phase transitions, according to the appearance of two peaks in the temperature dependence of magnetic entropy change curves. The temperature dependent resistivity data for both the systems display semiconductor nature near room temperature and insulating like behavior at low temperature regime. The variable-range hopping conduction mechanism is used to best understand their transport mechanism. In addition, the electrical polarization loop at low temperature confirms the presence of ferroelectricity for both the studied systems. The decreases polarization under an external magnetic field evidence the weak magnetoelectric coupling. The coexistence of FM ordering with insulating behavior and ferroelectricity at low temperature promises new opportunities and improvements in next generation applications for information storage, spintronic, and sensors.

Structural, electronic and superconducting properties of room temperature deposited VN[formula omitted] thin films

In recent years, vanadium mononitride (VN) thin films have emerged for their multifaceted functionalities e.g. as electrodes in battery and supercapacitors, as catalysts for hydrogen and oxygen evolution reactions, as superconductors for hot-electron bolometer detectors. In this study, we investigate the structural, electronic and superconducting properties of polycrystalline VNx thin films synthesized at room temperature using a reactive dc magnetron sputtering. The structural evolution of VNx samples with increase in partial N2 gas flow (RN2) during the reactive sputtering and corresponding change in the oxidation states were systematically studied. At a first glance, no visible changes appear in the lattice parameters within RN2= 5–50% samples. Despite this, only RN2 = 5 and 10% samples exhibit superconductivity. Probing the electronic structure around the V L-edges and O, N K-edge again did not reflect any minimal changes in RN2 = 5–100% samples. Across the V K-edge, the oxidation state was also found to be similar. However, the ambiguity was resolved from the Fourier transformed EXAFS spectra immediately revealing presence of a higher number of cationic vacancies. These vacancies drive the VNx system towards poor metals exhibiting dρ/dT = negative in the temperature dependent resistivity. This is in sharp contrast to the previous reports so far exhibiting positive slopes evident for metals. The present work insights on several ambiguities observed for the first time in the V-N system. The work further emphasizes the need to perform a similar study on epitaxially grown VNx thin film samples with reduced defects.