Resistivity Behavior Research Articles

Effect of thickness on metal-to-semiconductor transition in 2-dimensional TiN thin films

Titanium nitride thin films have been grown on c-plane sapphire substrates using a pulsed laser deposition technique in the thickness range of 6–45 nm. X-ray diffraction (XRD) analysis has demonstrated TiN (111) as the preferred orientation of growth on the sapphire substrates. The XRD measurements have also indicated that orientational alignment between the TiN and the sapphire improved with an increase in the TiN film thickness. A change in the resistivity behavior of the TiN thin films from metallic to semiconducting has been observed as the TiN film thickness is reduced below 15 nm. Analyzing and fitting of TiN films’ conductivity data have shown that while the Arrhenius law governs their conductivity in the temperature range of 300–350 K, conductivity values of the films follow the variable range hopping mechanism below 300 K.

Thermoelectric and magnetic properties of Ce3Cu3−xAuxSb4 compounds

We present the result of magnetic and thermoelectric investigations of the series of Ce3Cu3−xAuxSb4 compounds. The experimentally obtained data are discussed based on ab initio band structure calculations. It has been shown that structural disorder resulting from doping of Ce3Cu3Sb4 with Au induces a spin-glass-like behavior in the Ce3Cu3−xAuxSb4 series. All components x exhibit a negative temperature coefficient of the resistivity and metallic behavior of thermopower S(T) in the temperature region of T > 100 K. The maximal S value of 250 μV/K was measured for the pristine Ce3Au3Sb4 sample, while the highest figure of merit ZT = 0.06 was obtained for sample x = 1.5 at the highest measured temperature (T = 390 K).

Effects of magnetic field and particles content on rheology and resistivity behavior of magnetorheological elastomer with embedded cobalt particles

In most studies, carbonyl iron particles were merged with carbon-based particles such as graphite or carbon black particles as fillers to enhance the electrical properties of magnetorheological elastomers (MREs). These combined fillers can be replaced by using a single material in order to reduce brittleness due to the high amount of composition. Therefore, in this research, cobalt particles having dual properties, magnetic and electrical, have been employed as a filler in MRE. A total of three anisotropic MREs containing 53, 60, and 67 wt% of cobalt were fabricated through the mixing process method. The characterization related to morphological and magnetic properties of MRE samples was analyzed by using field emission scanning electron microscopy and vibrating sample magnetometer. Then, the rheological properties of the MRE in various strengths of magnetic field intensity between 0 and 0.8 T were conducted by using a rheometer. Afterward, the effect of the cobalt on the electrical properties was investigated and compared with different applied forces towards the MRE. The outcome showed that the rheological and electrical properties of MRE were improved with the increase of cobalt content embedded in the silicone matrix. Higher cobalt content in MRE contributed to a higher magnetorheological (MR) effect and simultaneously lower the electrical resistivity. Therefore, the addition of cobalt particles as a filler in MRE is a great potential to be applied as sensors.

Properties of indium tin oxide thin films grown by Ar ion beam sputter deposition

Indium tin oxide (ITO) thin films were grown by Ar ion beam sputter deposition under systematic variation of ion energy, geometrical parameters, and O2 background pressure and characterized with regard to the film thickness, growth rate, crystalline structure, surface roughness, mass density, composition, electrical, and optical properties. The growth rate shows an over-cosine, forward-tilted angular distribution with a maximum, which increases with increasing ion energy, increasing ion incidence angle, and decreasing O2 background pressure. ITO films were found to be amorphous with a surface roughness of less than 1 nm. Mass density and composition show only small changes with increasing scattering angle. The electrical resistivity behavior in dependence on the process parameters is complex. It is not only driven by the O2 background pressure but also very much by the scattering angle. The observed behavior can be understood only if competing processes are considered: (i) reduction of the number of oxygen vacancies due to the presence of O2 background gas and (ii) defect generation and preferential sputtering of oxygen at the surface of the growing films due to the impact of high-energy scattered particles. Even though absolute numbers differ, optical characterization suggests a similar systematics.

Percolation conductivity model in A site-deficient La0.8−xoxNa0.2−xoxMnO3 manganites and universal model of magnetic field-dependent resistivity and magnetoresistance behavior

The electrical and magnetoresistance behaviors of La0.8−xoxNa0.2−xoxMnO3 [with x = 0 (N0) and 0.1 (N0.1)] polycristalline samples were investigated. Resistance measurements versus temperature under different magnetic applied fields were performed to investigate the electronic transport as well as the magnetoresistance properties. The metal/insulator transition temperature decreases from 280 K for x = 0 to 275 K for x = 0.1. The electrical conduction in these compounds has been well described in the context of the percolation model based on the phase separation of ferromagnetic metallic regions with paramagnetic insulating ones. The temperature-dependent resistance shows the existence of a minimum at low temperature. This behavior is due to the existence of a competition between inelastic and elastic interactions expressed by Kondo-like spin-dependent scattering. An empirical model was used to describe the variation of the magetoresistance and normalized resistance as a function of the magnetic applied field. The model was successfully widely tested on several magnetic specimens and the evolution of the fitting parameters was discussed in detail.

Fabrication of an IPL-sintered Cu circuit and its electrochemical migration behavior

Problems associated with the oxidation of Cu nanopaste have been widely studied in efforts to develop a replacement for Ag nanopaste. The intensive pulsed light (IPL) sintering process has been suggested to solve the oxidation problem because it is a method with a short processing time and is conducted at room temperature. Cu nanopaste was fabricated with Cu nanoparticles and a functional organic matrix. Cu nanopaste screen-printed onto a polyethylene terephthalate substrate was subjected to various IPL sintering conditions, and the effects of pulse power and pulse width on the microstructure, electrical resistivity, and electrochemical migration behavior of the printed Cu patterns were investigated. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrochemical migration behavior was varied because of leaked ethylene glycol from organic matrix. The dendrites from lower pulse condition has finer microstructure and increased nucleation.

Structural and Magneto-Transport Properties of (1-x)La0.70Sr0.30MnO3 – (x)ErMnO3 (x = 0.00, 0.10, 0.20, and 0.30) Composite

(1-x)La0.70Sr0.30MnO3 (LSMO) – (x)ErMnO3 (EMO) (x = 0.00, 0.10, 0.20, and 0.30) ceramics were synthesized by chemical route. The structure characterization of all the samples was carried out at room temperature. The LSMO has rhombohedral symmetry with space group R-3C and EMO has hexagonal symmetry with space group P63/mcm. The temperature-dependent resistivity behavior of pure and composite samples has shown metal-insulator (MI) transition. The peak resistivity ρmax increases with decrease in MI transition temperature. Percentage magneto-resistance (MR) variation of LSMO-EMO (x = 0.10, 0.20, and 0.30) with temperature has also been studied. The result of ln (ρ) vs. Tn shows that conduction occurs due to variable range hopping (VRH) of electrons for x = 0.20 and 0.30. % MR data has been statically analyzed which shows the normal distribution.

Electrical transport and thermoelectric study of Ca3Co4O9 ceramics

The study of thermoelectric materials, which convert thermal energy to electrical energy in the solid state, has grown immensely in the past decade. The polycrystalline Ca3Co4O9 powder were synthesized using conventional sold state route by employing double sintering method. Homogeneous mixture in stoichiometric proportion of CaCo3 and Co3O4 powder was ground for 3 hrs and sintered at 1100 °C for 24 hrs with several intermediate grindings. The electrical transport property such as temperature dependent resistivity and thermoelectric seebeck coefficient was measured in the temperature range RT to 623 K. The electrical resistivity decreases with increasing temperature showing the semiconductor behaviour. The resistivity behaviour is fitted and explained using Thermal activation model and small polaron hopping (SPH) model. The value of seebeck coefficient (S) measured from room temperature to 623 K and it is found to be ∼42.7 μV/K. Ca3Co4O9 is thermoelectrically potential material for waste heat retrieval energy applications.

Thermopower Enhancement of Rutile-type SnO2 Nanocrystalline Using Facile Co-Precipitation Method

Metal oxide semiconductor has attracted so much attention due to its high carrier mobility. Herein, thermoelectric study of nanocrystalline SnO2 through a simple co-precipitation method is conducted to enhance the Seebeck coefficient (S). X-ray diffraction, thermogravimetric analysis (TGA), resistivity (r), Seebeck coefficient (S), and power factor (PF) measurements are conducted to analyze the thermoelectric properties of the material. The measurements show that there are two interesting results, which are the unusual resistivity behavior and the high value of the S. Resistivity behavior shows a non-reflective intermediate semiconductor-metals behavior where the turning point occurs at 250 o C. This behavior is strongly correlated to the surface oxide reaction due to annealing temperature. The maximum S likely occurs at 250 ºC, since the curve shows a slight thermopower peak at 250 ºC. The value of the S is quite high with around twenty times higher than other publications about SnO2 thermoelectric material, this happens due to the bandgap broadening. The energy gap of SnO2 calculated using density functional theory (DFT), which was performed by Quantum Espresso 6.6. The result shows that there is a broadening energy gap at different momentum or wave factor. Nanocrystalline semiconductors material is giving an impact to increase the width of bandgap due to quantum confinement and could enhance the thermopower especially in SnO2 nanocrystalline

Magnetic, magnetocaloric effect and resistivity behavior of Sb substituted MnAs

Magnetic, magnetocaloric effect and resistivity behavior of phase pure MnAs1−xSbx systems, synthesized by solid state reaction, have been studied for x up to 0.3. The systems display ferromagnetic metal to paramagnetic insulator transition and the transition temperature TC systematically decreases with increase in x. Arrot plot analysis indicate that the magnetic transition is of first order for all the samples though thermal hysteresis about TC is observed only for x up to 0.15. Isothermal magnetization measurements have been performed in four different protocols traversing distinctive thermodynamic paths and the isothermal magnetic entropy changes (ΔS) have been estimated using Maxwell thermodynamic equation. ΔS(T) exhibit similar asymmetric peak behavior for samples in the range 0.1–0.3 about the corresponding TC both in shape and magnitude, where as x = 0.05 sample exhibits sharp peak followed by a plateau for field change ΔH in the range 10–70 kOe. The value of extracted ΔS(T) is independent of the measurement protocol within the estimated error for all the samples. The calculated refrigeration capacity for two considered cases of hot and cold sink temperatures, viz. TC – 25 and TC + 25 K and temperatures at the full width half maximum is found to be same in all the samples for any ΔH in the range 10–70 kOe. Resistivity behavior in ferromagnetic region manifests contribution from electron-magnon scattering following T2 dependence and electron-phonon contribution following Bloch-Grüneisen formalism. Our analysis indicates lattice elongation is responsible for reduction in TC and Debye temperature ΘD. It is surmised that enhanced spin fluctuations are responsible for paramagnetic insulating behavior.

Systematical study of multi-walled carbon nanotube nanofluids based disposed transformer oil

In this paper, the electrical, dielectric, Raman and small angle X-ray scattering (SAXS) structure behavior of disposed transformer oil in the presence of multi-walled carbon nanotube (MWCNT) were systematically tested to verify their versatility for preparing better alternative transformer oil in future. MWCNT nanofluids are prepared using a two-step method with concentrations ranging from 0.00 to 0.02 g/L. The test results reveal that 0.005 g/L concentration possesses the most optimum performance based on the electrical (AC breakdown and lightning impulse) and dielectric (permittivity, dissipation factor and resistivity) behavior. According to the trend of AC breakdown strength and lightning impulse pattern, there were 212.58% and 40.01% enhancement indicated for 0.005 g/L concentration compared to the disposed transformer oil. The presence of MWCNT also yielding to the decrement of dissipation factor, increased on permittivity and resistivity behavior of disposed transformer oil which reflected to the performance of electrical properties. Furthermore, it is found that these features correlated to the structural properties as systematically verify by Raman and SAXS analysis study.

Effect of Fe Content on the Microstructure, Electrical Resistivity, and Nanoindentation Behavior of Zr60Cu40-xFex Phase-Separated Metallic Glasses

Effect of Fe Content on the Microstructure, Electrical Resistivity, and Nanoindentation Behavior of Zr60Cu40-xFex Phase-Separated Metallic Glasses

Electron–electron interaction dominated resistivity minimum in quasi-continuous Ag nanocluster films

Electronic transport in metal nanoclusters has great significance due to a variety of tunable parameters such as size, dimensionality, and cluster-distribution. Here, we report on the resistivity behavior of randomly distributed quasi-continuous Ag nanocluster films of varying cluster coverage on the substrate. This was achieved by changing the deposition time of clusters on the substrate. The Ag nanoclusters which were about 15 nm in size were deposited on thermally oxidized silicon substrates. As the deposition time reduced, clusters were distributed randomly with less coverage on the surface, resulting in a resistivity minimum at low temperatures. The temperature at which resistivity minimum occurs increases as the deposition time decreases. The resistivity at temperatures above 45 K was found to fit with a modified Bloch–Gruneisen equation which includes interaction of electrons due to structural disorder. However, the obtained Debye temperatures were found to decrease in comparison with the bulk values, which is ascribed to the softening of phonon modes in these structures. The emergence of the resistivity minimum could be explained through disorder effects in electron–electron interaction dominated quantum corrections, as shown in the Altshuler–Aronov model. A T1/2 temperature dependence of resistivity at low temperatures, as predicted by this model, was observed in our system, showing the applicability of this model.

Ti–Cu Coatings Deposited by a Combination of HiPIMS and DC Magnetron Sputtering: The Role of Vacuum Annealing on Cu Diffusion, Microstructure, and Corrosion Resistance

Titanium-copper (Ti–Cu) coatings have attracted extensive attention in the surface modification of industrial and biomedical materials due to their excellent physical and chemical properties and biocompatibility. Here, Ti–Cu coatings are fabricated using a combination of high-power pulsed magnetron sputtering (HPPMS; also known as high power impulse magnetron sputtering (HiPIMS)) and DC magnetron sputtering followed by vacuum annealing at varied temperatures (300, 400, and 500 °C). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) data showed that Ti, Cu, and CuTi3 are mainly formed in the coatings before annealing, while Ti3O, Cu2O, and CuTi3 are the main compounds present in the annealed coatings. The cross-sectional TEM micrographs and corresponding EDS results provided evidence that Ti is mainly present on the surface and interfaces of the silicon substrate and the Ti–Cu coatings annealed at 500 °C, while the bulk of the coatings is enriched with Cu. The resistivity of the coatings decreased with increasing the annealing temperature from 300 to 500 °C. Based on self-corrosion current density data, the Ti–Cu coating annealed at 300 °C showed similar corrosion performance compared to the as-deposited Ti–Cu coating, while the corrosion rate increased for the Ti–Cu coatings annealed at 400 and 500 °C. Stable release of copper ions in PBS (cumulative released concentration of 0.8–1.0 μM) for up to 30 days was achieved for all the annealed coatings. Altogether, the results demonstrate that vacuum annealing is a simple and viable approach to tune the Cu diffusion and microstructure of the Ti–Cu coatings, thereby modulating their electrical resistivity, corrosion performance, and Cu ion release behavior.

Impact of nanorod morphology on microstructure, magnetic and electrical properties of NixCo1-xFe2O4

A series of NixCo1-xFe2O4 (x = 0, 0.25, 0.5, 0.75 and 1) was successfully synthesized via hydrothermal method. From XRD analysis, the pure phase formation of Ni–CoFe2O4 (NCFO) was confirmed and the crystallite size ranged from 33 to 44 nm. Besides, the variation of theoretical lattice parameter with x-content was in a good agreement with experimental ones. Field Emission Scanning Electron Microscope (FESEM) revealed the formation of nanorod shapes with gradual decrease in length and diameter with addition of Ni2+ ions. Energy Dispersive X-ray analysis (EDX) confirmed the purity of prepared samples. Magnetic parameters (Ms, Mr and Hc) showed a gradual decrease with addition of Ni2+ ions. Meanwhile, both Coercivity and Curie temperature were enhanced in our studied nanorod compositions compared to their corresponding nanosphere compositions. Variation of DC resistivity and thermoelectric power coefficient were studied in the temperature range 385–548 K. The sign of the thermoelectric power coefficient could determine the type of charge carriers. Moreover, the conduction mechanism was deduced from activation energy values. Finally, the cation distribution was proposed such that it could verify the variation of lattice parameter and magnetization of each composition as well as the behavior of resistivity and thermoelectric power.

The resistivity upturn in Ni–Mn–In alloys exhibiting magnetic field induced shift in martensitic transition with and without Co doping

The temperature dependent resistivity behavior of Ni2Mn1+xIn1−x (0.32 ≤x≤ 0.48), Ni1.81Co0.22Mn1.46In0.51 and Ni1.81Co0.22Mn1.45In0.52 is studied with and without applied magnetic field. These alloys exhibit inverse magnetocaloric effect and giant magnetoresistance that are important for applications like magnetic refrigeration and magnetic sensors. The properties arise due to shift in martensitic transition to lower temperature with applied magnetic field. The doping of Co at Ni site and Mn at In site affects the disorder in the system. The disorder is an important factor that decides the requirement of magnetic field for applicability. In present manuscript, the effect of disorder is studied through resistivity behaviour. The resistivity upturn is observed at low temperature. The upturn is fitted by least square method. The fitting reveals nature of disorder, origin of low temperature resistivity behavior with magnetic field, and consequently reveals the cause of difference in magnetic field induced large shift in martensitic transition to lower temperature with composition. The results reveal that long-range antiferromagnetic coupling and balance of Co and Mn doping amount is desired in new material design for technical applications.

Structure, electrochemical impedance and Raman spectroscopy of lithium-niobium-titanium-oxide ceramics for LTCC technology

Resultsof Electrochemical Impedance Spectroscopy (EIS) are reported for lithium-niobium-titanium-oxide (LNTO) ceramics synthesized by a solid-state reaction method with two functional additives (MoO3 or ZnO) in the temperature range 323 K - 573 K and frequencies between 10−1 Hz and 107 Hz. Scanning electron microscopy (SEM) reveals a textured morphology of rod and plate-like particles that are typical for M-phase LNTO materials, while X-ray diffraction (XRD) analysis confirms the formation of an M-phase member compound with an approximate structure of Li7Nb3Ti5O21. Complex impedance analysis indicates that its overall electrical resistivity behavior depends mostly on the grain boundary processes. EIS analysis shows a negative temperature coefficient of resistance behavior (NTCR) in a defined temperature range in two LNTOs and thermal activation of the conduction mechanisms. The low dielectric constants of 5.5 and 12.1 at 1 MHz were found for the first and second LNTOs, respectively. Complimentary Raman spectroscopic measurements, despite very large crystallographic unit cell of LNTO, reveal only a small number of lines, which is the consequence of a “molecular” nature of materials.

Structural Features, Anisotropic Thermal Expansion, and Thermoelectric Performance in Bulk Black Phosphorus Synthesized under High Pressure.

Black phosphorus (BP) allotrope has an orthorhombic crystal structure with a narrow bandgap of 0.35 eV. This material is promising for 2D technology since it can be exfoliated down to one single layer: the well-known phosphorene. In this work, bulk BP was synthesized under high-pressure conditions at high temperatures. A detailed structural investigation using neutron and synchrotron X-ray diffraction revealed the occurrence of anisotropic strain effects on the BP lattice; the combination of both sets of diffraction data allowed visualization of the lone electron pair 3s2. Temperature-dependent neutron diffraction data collected at low temperature showed that the a axis (zigzag) exhibits a quasi-temperature-independent thermal expansion in the temperature interval from 20 up to 150 K. These results may be a key to address the anomalous behavior in electrical resistivity near 150 K. Thermoelectric properties were also provided; low thermal conductivity from 14 down to 6 Wm-1K-1 in the range 323-673 K was recorded in our polycrystalline BP, which is below the reported values for single-crystals in literature.

Quantitatively determining the degree of spin fluctuations in actinide metals and compounds

Actinide materials are well-documented for nuclear properties, but their 5f electrons that produce exotic phenomena are not, due to the complexity of a dual localized and itinerant nature that remains a mystery. Particular interest is given to the electronic correlations at the localized and itinerant boundary where strong spin fluctuations are present. We report the identification of an intensity defined by integrating the normalized resistivity that approximately provides a quantitative measure of spin fluctuations. The intensity is very sensitive to the tuning of non-thermal parameters such as pressure and chemical doping, probing the anomalies in the evolution of spin fluctuations close to a valence or magnetic instability. In this way, our results are not only connected with the long-standing controversy on the anomalous low-temperature resistivity behavior of actinide metals, but also highlight an unconventional type of superconducting pairing, mediated by valence and/or spin fluctuations, for a wealth of 4f and 5f-electron systems. In an unified picture proposed, it is helpful to determine the degree of spin fluctuations for understanding the origin of the emergent superconductivity in systems with correlated electrons.

Correlation of cation distribution with structure, magnetic and electrical properties of ultrafine Ni2+-doped CoFe2O4

This work presents the estimation of cation distribution of ultrafine NixCo1−xFe2O4 nano-ferrites (x = 0, 0.25, 0.5, 0.75 and 1) from structure, magnetic and electrical investigations. “Sol gel” was the method used to synthesize Ni–Co ferrites. Ni2+-doped CoFe2O4 nanostructure has a broad range of electromagnetic applications due to its controllable magnetic and electrical properties. From XRD patterns, the formation of pure phase was obvious, and the crystallite size ranged from 9 to 12 nm. These sizes are small enough to achieve suitable signal-to-noise ratio for high-density recording media and have more opportunities for technological application, especially in medical fields. Besides, the variation of theoretical lattice parameter with x-content was in a good agreement with experimental ones. Field Emission Scanning Electron Microscope (FESEM) revealed the formation of small nanosphere particles with gradual size reduction on addition of Ni2+ ions. Energy-Dispersive X-ray analysis (EDX) confirmed the purity of prepared samples. Magnetic parameters (Ms, Mr and Hc) were determined from Vibrating Sample Magnetometer (VSM). It was found that both Ms and Hc have gradual decrease with increasing x-content. Curie temperature was determined from the variation of relative permeability with temperature and showed also a gradual decrease with addition of Ni2+ ions. Temperature dependence of both DC electrical resistivity and thermoelectric power coefficient were carried out in the temperature range 385–548 K. The resistivity showed a gradual decrease with increasing x-content. However, the negativity of thermoelectric power coefficient showed a gradual increase with addition of Ni2+ ions. Conduction mechanism was deduced for all studied samples from activation energy values. The cation distribution was proposed such that it could verify the lattice parameter and magnetization of each composition as well as the behavior of resistivity and thermoelectric power.