Temperature-dependent Resistivity Measurements Research Articles

Achieving p-type conductivity in wide-bandgap SnO2 by a two-step process

Wide bandgap SnO2 usually shows n-type conductivity due to intrinsic defects. Herein, we demonstrate the achievement of p-type conduction in SnO2 with a two-step process, in which 3.3 at. % Mg-doped SnO2 epitaxial films were first grown on c-Al2O3 by pulsed laser deposition and then annealed in an oxygen atmosphere at proper temperature and time. An activation energy of around 85 meV revealed by temperature-dependent resistance measurements verifies Mg as a shallow acceptor in the p-type doping of SnO2. The post-annealing treatment at suitable temperature and time was found to be crucial to greatly enhance the p-type conductivity of Mg-SnO2 by removing the interstitial Mg while maintaining the substitutional Mg in the SnO2 lattice. A hole concentration of 1.43 × 1017 cm−3 and a hole mobility of 4 cm2 V−1 s−1 as determined by Hall-effect measurements were achieved for a sample annealed at optimized conditions of 600 °C and 0.5 h. The achievement of high-quality p-type Mg-SnO2 epitaxial films demonstrates high potential in developing advanced optoelectronic devices based on p-n junctions of SnO2.

Two-transition behavior in Bi0.5Sb0.5SeI crystals

The ions with outer electron configuration of ns2 are often considered key factors for the efficient carrier transport in optoelectronic materials. In many cases precise tuning of the band gap and adjustment of the desired electronic properties achieved through the changes of the chemical environment. Here we investigate BixSb1-xSeI (x = 0.5) mixed crystals that have a one-dimensional structure with intermediate physical parameters between BiSeI and SbSeI compounds. Although crystallographically the substitution appears to be trivial, we found, that it has a rather strong effect on chemical bonds that provoke two-mode Raman behavior as well as two electronic transitions. The temperature dependent electrical resistance and photoluminescence measurements indicated anomalies at ~146 and ~62 K with strong thermal hysteresis loop for Bi0.5Sb0.5SeI. These, mixed samples inherit anisotropic properties, but inhomogeneity prevail the structure. We assert that the difference in masses of bismuth and antimony should be responsible for the observed binary effect.

Suppression of multiple magnetic ordering induced by Nb and Ru substitution in SrCoO3-δ systems

Abstract In this paper, we report detailed study on magnetic behavior of perovskite SrCoO3-δ compound with partial substitution of non-magnetic Nb and magnetic Ru at Co site. All the samples show single-phase nature with tetragonal structure of P4/mmm space group. The semiconducting behavior is evident from temperature dependent resistivity (ρ) measurement. The resistivity exhibits Variable Range Hopping and Small Polaron Hopping mechanisms in different temperature regimes. The magnetoresistance increases with substitution and reaches up to ~35% at 10 K with 70 kOe magnetic field. The samples show weakly ferromagnetic-type transition below room temperature. The saturation magnetization and exchange bias (EB) increase with Nb concentration but the effect is less prominent for Ru substituted samples. Different magnetic properties are explained on the basis of valence states of Nb5+ and mixed valence of Ru4+/5+ replacing Co3+. The existence of ferromagnetic correlated region in antiferromagnetic matrix and irreversible glass state with competing exchange interactions impart the EB effect in these samples. The EB value HEB~7.45 kOe at 10 K is quite significant which might be useful for further technological implementation in electronics/spintronics devices.

Tunable n-Type Conductivity and Transport Properties of Cubic Boron Nitride via Carbon Doping

The recent discovery of direct conversion of hexagonal boron nitride (h-BN) into quenched BN (Q-BN) and single-crystal cubic BN (c-BN) by pulsed laser annealing (PLA) have been implemented to fabricate carbon-doped c-BN with dopant concentration ranging from 2 × 1019 to 7 × 1021 cm–3. Micro Raman analysis shows a total conversion of h-BN into phase-pure c-BN, whereas the X-ray diffraction (XRD) confirms the presence of the cubic structure with (111) epitaxy on c-sapphire. Hall measurements demonstrate the n-type electrical property, and the temperature-dependent resistivity measurements confirm the semiconductor-like profile of the doped c-BN. Consistent changes in resistivity, Hall mobility, and other electrical properties were investigated with the variance in dopant concentration level. We have observed a shift in the conduction mechanism with temperature from the resistivity vs temperature analyses. At the high-temperature regime (130–330 K), the activation energy lies in between 0.012 and 0.074 eV, whereas at the low-temperature regime (20–130 K), the activation energy was obtained to be in between 0.0024 and 0.0083 eV. The lower values of activation energies, showing a complete ionization of the impurity atoms even at room temperature, are surmised to result from dopant-profile broadening. The enhanced electrical activation and superior quality c-BN films open exciting avenues for next-generation device applications.

Impurity band conduction in Si-doped β -Ga2O3 films

By combining temperature-dependent resistivity and Hall effect measurements, we investigate donor state energy in Si-doped β-Ga2O3 films grown using metal-organic vapor phase epitaxy. High-magnetic field (H) Hall effect measurements (–90 kOe ≤ H ≤ +90 kOe) showed non-linear Hall resistance for T < 150 K, revealing two-band conduction. Further analyses revealed carrier freeze out characteristics in both bands yielding donor state energies of ∼33.7 and ∼45.6 meV. The former is consistent with the donor energy of Si in β-Ga2O3, whereas the latter suggests a residual donor state. This study provides critical insight into the impurity band conduction and the defect energy states in β-Ga2O3 using high-field magnetotransport measurements.

Decoupling the metal insulator transition and crystal field effects of VO2

VO2 is a highly correlated electron system which has a metal-to-insulator transition (MIT) with a dramatic change of conductivity accompanied by a first-order structural phase transition (SPT) near room temperature. The origin of the MIT is still controversial and there is ongoing debate over whether an SPT induces the MIT and whether the Tc can be engineered using artificial parameters. We examined the electrical and local structural properties of Cr- and Co-ion implanted VO2 (Cr-VO2 and Co-VO2) films using temperature-dependent resistance and X-ray absorption fine structure (XAFS) measurements at the V K edge. The temperature-dependent electrical resistance measurements of both Cr-VO2 and Co-VO2 films showed sharp MIT features. The Tc values of the Cr-VO2 and Co-VO2 films first decreased and then increased relative to that of pristine VO2 as the ion flux was increased. The pre-edge peak of the V K edge from the Cr-VO2 films with a Cr ion flux ≥ 1013 ions/cm2 showed no temperature-dependent behavior, implying no changes in the local density of states of V 3d t2g and eg orbitals during MIT. Extended XAFS (EXAFS) revealed that implanted Cr and Co ions and their tracks caused a substantial amount of structural disorder and distortion at both vanadium and oxygen sites. The resistance and XAFS measurements revealed that VO2 experiences a sharp MIT when the distance of V–V pairs undergoes an SPT without any transitions in either the VO6 octahedrons or the V 3d t2g and eg states. This indicates that the MIT of VO2 occurs with no changes of the crystal fields.

Evaluation of crystallographic and electrical-superconducting features of Bi-2223 advanced ceramics with vanadium addition

In the current study, the effect of vanadium particles on the electrical, superconducting, crystallographic, key structural and morphological features of Bi1.8Sr2.0Ca2.2Cu3.0VxOy superconducting materials is examined with the aid of powder X-ray diffraction (XRD), scanning electron microscope (SEM), electron-dispersive X-ray (EDX) and dc electrical resistivity over the temperature (ρ-T). The vanadium-added Bi1.8Sr2.0Ca2.2Cu3.0VxOy (Bi-2223) superconducting materials are prepared within the molar ratios between x = 0.00 and 0.30 using the conventional solid-state reaction technique. The temperature-dependent electrical resistivity measurements show that the existence of vanadium atom in the superconducting system damages seriously the Bi-2223 (high-Tc) phase content in the crystal structure as a result of the formations/disappearances of new impurity phases. On this basis, the amplitude Ψ0 of wave function founded on the super-electrons is considerably reduced with the vanadium addition. The critical onset and offset transition temperature values truncate from the values of 110.92 K and 97.45 K to 103.17 K and 18.38 K in case of the maximum vanadium addition level of x = 0.30. Similarly, the XRD results present that the average crystallite size and c-axis length parameters are noted to decrease considerably whereas a-axis length, strain and relativistic dislocation density ratios are calculated to enlarge harshly depending on the addition content level. It is also obtained that the vanadium inclusions lead to increase seriously the permanent crystal structure problems, disorders, misorientations, lattice strains, crack-producing omnipresent flaws and grain boundary coupling problems in the active Cu–O2 consecutively stacked layers in the superconducting core, being assured by SEM analyses. Besides, the SEM results show that the enhancement of vanadium addition level in the crystal structure damages remarkably the flaky layers of platelet-like shape for the grains. In fact, the excess vanadium addition seriously damages the general characteristic view (flaky layer structure) of Bi-2223 compound. Based on the EDX findings, the main reason for the degradation of fundamental characteristic properties of Bi-2223 system may stem from the possible replacement of aliovalent vanadium impurities for the copper-sites in the crystal structure. Namely, the vanadium addition in the crystal structure is ploughed to improve the fundamental crystallographic and electrical-superconducting features of bulk Bi-2223 superconducting materials.

Evaluation of magnetotransport properties of Au added YBCO ceramics: combination of experimental and advanced theoretical approaches

The purpose of this work is to investigate the change of flux pinning ability, superconducting and physical properties of gold particle addition in the YBa2Cu3O7-x (YBCO) superconducting matrix using temperature dependent resistivity measurements under different applied magnetic fields; namely 0.0, 0.3, 1.0, 2.0, 5.0 and 7.0 T. The room temperature resistivity, transition temperature (Tc), transition width (∆Tc) and mobile hole carrier concentration values for each sample have separately been determined. In addition, we estimated the field-dependent activation energy (U0), irreversibility field (µ0Hirr), upper critical field (µ0Hc2), penetration depth (λ) and coherence length (ξ) with the quantum mechanical approaches related to the fluxoid mechanism for all the samples prepared. It was found that the flux pinning energy values evaluated by Thermally Activated Flux Creep (TAFC) model were determined to be about 11,455 K, 13,413 K, 10,350 K and 9320 K for the undoped, 1 wt%, 5 wt% and 20 wt% Au doped samples, respectively. Moreover, the results obtained showed that the critical temperature, activation energy, irreversibility and upper critical field values were found to depend strongly on the gold content and applied magnetic field strength. The values of µ0Hirr, µ0Hc2, λ and ξ (∆Tc) initially exhibited a slight increment (decrement) followed by a decrease (increase) for the samples with the higher gold-doping concentrations. The possible reasons regarding the observed changes in flux pinning and fundamental superconducting properties due to gold-doping in YBCO superconductors were discussed in detail. We indicated that a certain amount of gold doping has an effective role to form the nucleation centers that serve as the active flux pinning regions in the YBCO system so that the quality of interaction between the superconducting grains and inter-granular coupling strength in the adjacent multilayers can increase remarkably.

Temperature-Dependent Magnetoresistance in Polycrystalline Ni81Fe19 Thin Film on Si (100)

Magnetoresistance (MR) in thin films stems from different types of scattering mechanism present in the film. We report a systematic study of the temperature-dependent magnetoresistance behaviour in the pulsed DC magnetron sputtered Ni81Fe19 thin film on Si (100). X-ray diffraction study reveals the polycrystalline nature of the film along with the presence of preferred orientation. X-ray reflectivity measurement shows very low interface roughness (0.55 ± 0.04 nm). Temperature-dependent resistivity measurement is performed over a temperature range of 25–300 K, unveiling the dominance of electron-magnon scattering and impurity scattering at lower temperature (25–250 K) and electron-phonon scattering at higher temperature (above 250 K). In the investigated temperature range (30–300 K), the MR magnitude is found to reduce from 0.97 to 0.51% with increment in measurement temperature from 30 to 300 K. This reduction is attributed to the enhancement in phonon scattering at higher temperatures, and relatively suppressed ordering influence of magnetic field at higher temperature due to higher thermal activation energy and impurity scattering.

Atypical transport for GdTe1.8 upon substitution with Se: Strong electron-phonon coupling in polaronic conduction

The chemistry of new materials and the effects of chemical substitutions on physical properties continues to be of intense interest as it directly affects many technological fields. The synthesis and temperature dependent transport properties of GdTe1.62Se0.18 were investigated revealing polaronic transport upon simple alloying with selenium. Temperature-dependent resistivity and thermopower measurements indicate strong electron-phonon coupling, as compared to the few other chalcogenides that display such transport. In addition, the low thermal conductivity is intrinsic for this material, and a result of the stacking arrangement in the crystal structure as well as of a statistical disordered Te22– anion.

Structural, Optical and Electrical Properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 Pyrochlore Ceramics

Abstract Herein, the structural, morphological, compositional, optical, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 (BZN) solid solutions are reported. Tungsten substituted BZN ceramics which are fabricated by the solid state reaction technique exhibited solubility limits at substitution level below x=0.18. Remarkable engineering in the structural, optical, electrical and dielectric properties of the pyrochlore ceramics is achieved via W substitution. Namely, shrinkage in both of the lattice parameters and in the energy band gap accompanied with decrease in the microstrain, in the dielectric constant and in the electrical resistivity is observed upon increasing the W content below the solubility limit. The increase in the W content in the BZN ceramics enhances the densification of the pyrochlore and leads to higher light absorbability and larger crystallites growth. The temperature dependent electrical resistivity measurements has also shown that the pyrochlore exhibit thermal stability below 380 K.

Influence of hydrostatic pressure on hidden order, the Kondo lattice, and magnetism in URu2Si2−xPx

Within the chemical substitution series ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2\ensuremath{-}x}{\mathrm{P}}_{x}$, there is an evolution in the ground-state behavior from hidden ordered (HO) for $x\ensuremath{\lesssim}0.03$, to Kondo lattice behavior with no ordering (NO) for $0.03\ensuremath{\lesssim}x\ensuremath{\lesssim}0.26$, to antiferromagnetism (AFM-2) for $0.26\ensuremath{\lesssim}x\ensuremath{\lesssim}0.5$ [A. Gallagher et al., Nat. Commun. 7, 10712 (2016); A. Gallagher et al., J. Phys.: Condens. Matter 29, 024004 (2016)]. To better understand what factors control this behavior, temperature-dependent electrical resistivity measurements are performed for this series under applied pressures $P$ up to 20.5 kbar. Specimens in the HO $x$ region show similarities to the parent compound, where HO transforms into antiferromagnetism (AFM-1) at a critical pressure (${P}_{\mathrm{c}}$). ${P}_{\mathrm{c}}$ decreases with increasing $x$ and collapses towards $P=0$ near $x\ensuremath{\approx}0.03$, suggesting that AFM-1 occurs at ambient pressure for this concentration. No pressure-induced phase transitions are observed in the NO $x$ region and the AFM-2 state is only weakly suppressed by $P$. Measurements further reveal that AFM-1 and AFM-2 are distinct from each other. Calculations of the wave functions using the tight-binding Hartree-Fock approximation are performed and show (i) that the radial probability distributions for the phosphorus ions are more tightly bound than those for the silicon and (ii) that the energy difference between the orbitals decreases with increasing $x$. The cumulative effect of these two factors is that $\mathrm{Si}\ensuremath{\rightarrow}\mathrm{P}$ substitution decreases the hybridization strength, which correlates with the weakening of HO. At large $x$, additional effects such as electrical charge tuning also play an important role in determining the ground-state behavior.

The effect of heat treatment on the FeCo phase in Tb-Fe-Co thin films

Investigation of the magnetic behavior of nanostructured Tb-Fe-Co thin films before and after heat treatment below and above Fe-Co phase crystallization temperature has explored by electron microscopy (SEM), X-ray diffraction (XRD), temperature-dependent resistivity, magnetization (MOKE), magneto-resistivity, and Hall resistivity measurements. The thin films are composed of fine crystallites (from 10 to 75 nm) after heat treatment around the FeCo phase crystallization temperature obtained from XRD and SEM measurements. The nanostructured thin films show the unique perpendicular magnetic properties in the out-of-plane direction around the room temperature. The maximum squareness ratio value of as-deposited thin film with 10 nm crystallite size is 0.98, and the maximum coercive field value of 400∘C thin film with 60 nm crystallite size is 3897 Oe. Our findings offer a different perspective for synthesizing the nanostructured Tb-Fe-Co thin films for promising applications in the magnetic sensor technologies.

Investigation of metal-insulator transition temperature and magnetic properties of NdNiO3 nanoparticles

The control of metal–insulator transition (MIT) and magnetic properties of rare-earth nickelates remains a fundamental problem in material science. Here, we report a possible way to tune the MIT as well as the magnetic properties of NdNiO3 by reducing the crystalline size to the nanoscale. NdNiO3 nanoparticles of different sizes have been synthesized by a simple aqueous solution-based chemical method in the atmospheric pressure under oxygen. The x-ray diffraction study shows the formation of orthorhombic nanocrystals of NdNiO3 with Pbnm space group, presence of oxygen vacancies and higher octahedral distortion. The morphology and the particle size distribution have been evaluated by FESEM and TEM. The temperature dependent resistivity measurement shows the metal to insulator transition, which depends on the particle size; lower the particle size, higher the MIT temperature (TMI). Further study on the temperature dependent magnetic susceptibility shows the signature of magnetic phase transition at a temperature (Néel temperature TN), lower than the TMI, which indicates the existence of second order magnetic phase transition in our NdNiO3 nanoparticles. We have attributed the higher TMI and the origin of second order magnetic phase transition predominantly to the higher NiO6 octahedral distortion and the narrowing of bandwidth of the nanocrystalline NdNiO3, which leads to the opening of the charge transfer gap at the temperature higher than the bulk.

Magnetic and transport properties of inverse Heusler compound Cr2CoAl

We report magnetic and electrical transport properties of polycrystalline as-cast compound Cr2CoAl having inverse Heusler like XA structure with B2 disorder. Temperature-dependent magnetization (M-T) under zero-field cooled (ZFC) and field cooled (FC) condition and field-dependent magnetization (M-H) studies suggest that this compound is a soft magnetic material below Tc ~ 20.5 K having a very low magnetic moment as it is found that magnetization at 5 K under 50 kOe applied magnetic field is ~0.11μB/f.u. Also, M-T data taken ZFC-FC condition under different applied magnetic fields and M-H data taken at 100 K and 300 K indicate that this compound may have magnetic clusters in paramagnetic matrix. Further analysis and temperature-dependent heat capacity measurement reveal paramagnetic to a short-range ordered ferromagnetic transition near Tc ≈ 20.5 K and also reveal the presence of magnetic clusters within the compound. These magnetic clusters may arise because of B2 disorder in the compound. Temperature-dependent resistivity measurement confirms that the compound Cr2CoAl is metallic as it is found increasing with temperature. Nonlinearity in temperature dependency resistivity data, observed in low- temperature region, follows T2 dependency that generally comes because of electron–electron scattering. Magneto-resistance (MR) is also found to be positive throughout the temperature region from 8 K to 390 K.

First-order transition in trigonal structure CaMn2P2

We report structural and physical properties of the single crystalline . The X-ray diffraction (XRD) results show that adopts the trigonal -type structure. Temperature-dependent electrical resistivity measurements indicate an insulating ground state for with activation energies of 40 meV and 0.64 meV for two distinct regions, respectively. Magnetization measurements show no apparent magnetic phase transition under 400 K. Different from other , Sr, and Ba, and , As, and Sb) compounds with the same structure, heat capacity and reveal that has a first-order transition at and the transition temperature shifts to high temperature upon increasing pressure. The emergence of plenty of new Raman modes below the transition, clearly suggests a change in symmetry accompanying the transition. The combination of the structural, transport, thermal and magnetic measurements points to an unusual origin of the transition.

Spin valve effect in sputtered FL-MoS2 and ferromagnetic shape memory alloy based magnetic tunnel junction

In the last decade, two-dimensional (2D) transition metal dichalcogenides have been introduced with great significance in the spintronic devices for their extraordinary electrical, optical, and spin-dependent properties. In this work, we have fabricated a few-layer molybdenum disulfide (FL-MoS2) (~6 nm) as a non-magnetic spacer layer in Ni–Mn–In/FL-MoS2/Ni–Mn–In magnetic tunnel junction (MTJ) using DC magnetron sputtering. FL-MoS2 thin film sandwiched between two ferromagnetic shape memory alloy based electrodes exhibit semiconducting behavior, confirmed by current-voltage (I–V) characteristics and temperature dependent resistance measurement. The fabricated MTJ shows spin valve effect in the presence of an external magnetic field. The tunneling magnetoresistance (TMR) has been recorded in 10 K–300 K temperature range. The highest TMR ratio of 0.51% was obtained at a low temperature ~10 K, corresponding to the spin polarization of ~5%. This TMR ratio reduces to a value of 0.032% as the temperature of the device increases up to 300 K, displaying a finite TMR at room temperature. A detailed study of thickness and temperature-dependent magnetization versus magnetic field (M − H) hysteresis loops of Ni–Mn–In thin films has been performed to understand the complex TMR behavior. The present study paves the way for the use of sputtered FL-MoS2 and ferromagnetic shape memory alloy in ultrafast spintronics for advanced magnetic devices application.

Direct evidence for structural transformation and higher thermal stability of amorphous insbte phase change material

The search for novel phase-change materials with enhanced electrical and thermal properties are utmost importance for the development of reliable next-generation high-speed, non-volatile random access memory (NVRAM). In this paper, we investigate local structural change and crystallization kinetics of ternary InSbTe thin films using temperature-dependent resistivity measurement and in situ X-ray diffraction by synchrotron radiation source. Our experimental results reveal that crystallization of InSbTe begins with the formation of binary phases (InSb and InTe). Furthermore, cubic In3SbTe2 phase is emerged at 300 °C and remains stable up to 410 °C. The calculated values of texture coefficient indicate an increased orientation of In3SbTe2 phase upon increasing the temperature. Also, higher activation energy of 5.2–5.6 eV for crystallization is observed using Kissinger's method. These enhanced electrical, thermal and structural properties of InSbTe thin films would be suitable for high-speed NVRAMs as well as multi-bit data storage applications.

Characterization of the CoFe2O4/Cu displacement effect in the Y123 superconductor matrix on critical properties

In this study, CoFe2O4 (x = 0, 5, 10 and 20 wt%) doped YBa2Cu3−x(CoFe2O4)xO7−δ bulk samples were produced using solid state reaction (SSR) method and sol–gel(SG) methods. Oxide-form and acetate-form powders were preferred for SSR method and SG method, respectively. The heat treatment of the produced samples was carried out in two stages. Firstly, the samples were annealed at 950 °C for 24 h, after which they were kept in oxygen at 500 °C for 5 h and allowed to be cooled down to room temperature. Characterization of all samples was performed using methods such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, temperature-dependent resistance measurement (R–T) and Vickers microhardness analysis. Superconducting behavior was observed in all the produced samples, but as a result of the addition, a decrease was observed with the increase of the doping ratio at the critical transition temperature. As a result of the characterization, it is concluded that the doping ions can be replaced with Cu atoms in Y123 structure. In addition, doping led to significant changes in Vickers microhardness results.

Novel plasma-assisted combustion route for NiOx thin film deposition

The emerging field of flexible electronics demands low-temperature, high-throughput solution-processable thin films of oxide semiconductors. Towards this goal, we report a novel low-temperature synthesis route that is primarily in a combination of solution combustion synthesis and plasma irradiation to deposit p-type nonstoichiometric NiOx thin films at a relatively lower temperature range. The film morphology was studied by atomic force microscope (AFM) and scanning electron microscope (SEM) while the crystallographic information was obtained from X-ray diffraction (XRD) studies. The NiOx formation mechanism is extensively studied with X-ray photoelectron spectroscopy (XPS) measurements. Here we reveal the conditional analysis to optimize the Ni3+ concentration that essentially controls the net free carrier in the nonstoichiometric NiO thin films. Based on our understanding, the plasma treatment not only plays a deterministic role in the material and the defect formation but is also efficient in removal of chemical impurity to obtain crystalline NiO thin films. Temperature-dependent (130–303 K) electrical resistivity measurements revealed that variable-range hopping (VRH) is the dominant hole transport process in this material.