Papers by Keyword: Electrical Transport

Abstract: Electrical transport in materials have been studied extensively due to its great potential in spintronic technology. The introduction of the secondary phase into the manganite matrix can modify the electrical properties, subsequently improving the low-field magnetic resistance (LFMR). In this work, we study the change in electrical properties at different temperatures of polycrystalline (1-x)La_0.7Sr_0.2Ca_0.1MnO₃/xTiO₂ (LT) composites where x = 0, 0.05 and 0.1. Polycrystalline La_0.7Sr_0.2Ca_0.1MnO₃ (LSCMO) was synthesized by sol-gel method, calcined at 700 °C, and pre-sintered at 800 °C for 6 h before adding TiO₂. TiO₂ as filler was mixed with LSCMO by wet mixing and stirring for about 30 min until a homogeneous compound was formed. Composite LT was then inserted to oven up to 100 °C for 2h to remove the moisture, compacted at 10 MPa, and sintered at 1200°C for 12 h. All samples in the LSCMO phase have a rhombohedral crystal structure with space group R3c. The crystal structure parameters were studied using Rietveld refinement through GSAS II software. The sample was characterized by SEM to represent the morphology of the sample. As the TiO₂ content increased, the magnetization decreased, as observed by VSM analysis at room temperature. The electrical transport properties of pure LSCMO and LT were characterized by cryogenic from 195K to 260 K. The resistivity of LT10 is too high compared to that of LT5 and as the temperature increases, the resistivity in this range will decrease. For 200 K, the resistivity of LSCMO, LT5 and LT10 are 3.09 x 10^-2 ohm.cm, 4.40 x 10³ ohm.cm and 4.77 x 10⁴ ohm.cm respectively.

Abstract: A series of polycrystalline bulk samples (Pr_0.67Sr_0.33MnO₃)_1-x/ (NiO)_x were prepared by solid state reaction, and its structure, electrical transport and magnetoresistance properties were investigated. X-ray analysis showed that parent compound of Pr_0.67Sr_0.33MnO₃ (PSMO) formed in single phase with crystal structure of orthorhombic while secondary phase of NiO can be detected with the addition of composite. The electrical properties showed that the resistivity increased with the addition of NiO due to enhancement of spin dependent-tunneling scattering across the artificial grain boundaries of NiO layer. Magnetic field dependence MR curve at various temperatures clearly indicates that extrinsic magnetoresistance had been enhanced due to addition of NiO as the artificial grain boundary.

Abstract: In this paper, nanosized La_0.85Na_0.15MnO₃ (LNMO) has been synthesized via sol-gel method by involving two major steps, first the complexation of citric acid (CA) with metal ions (MI) and second the polyesterification between CA and ethylene glycol (EG). The effect of molar ratio CA:MI varying from 2-4 on structure, microstructure and electrical transport properties of LNMO have been investigated by constant the amount of EG. All samples show single perovskite phase with hexagonal structure and space group R3c after sintering at 800°C for 10h. Sample of molar ratio 2.5 is observed to possess smallest grain sizes which yield high resistivity value compared with others, is suggested to originate from the increase of tunneling barriers (grain boundaries). The large low field magnetoresistance (LFMR) of about ~ -16% at 0.1T and low temperature confirmed the important role of grain boundaries in the nanosized LNMO.

Abstract: The Underground is one of the most important means of transport providing high passengers’ transportability. Along with plentiful advantages such as high speed, ecological compatibility, high safety and others the Underground has a considerable disadvantage, that is,high energy consumption. Nowadays perspective directions of efficiency increasing are the development and introduction of advanced electrical vehicles technologies and new methods of brake-release mode optimization.

Abstract: In this report, manganite thin films of La_0.7Sr_0.3MnO₃ (LSMO) of various thicknesses are carried out by using Chemical Solution Deposition (CSD) technique on (100) – oriented single crystalline LaAlO₃ (LAO) substrate. Desired film thickness was achieved via control of the number of deposition sequences. X-ray diffraction (XRD) study shows that 1^st and 3^rd coatings of LSMO films have the cubic structure while 5^th and 7^th coatings of LSMO films have hexagonal structure. As the film thickness increases, increase in lattice parameter (c) was observed. Surface morphological study was carried out using Atomic Force Microscopy (AFM). RMS roughness and grain size were found to increase with the thickness. It is interesting and noticeable that the structural transition occurs from cubic to hexagonal are clearly observed through XRD and AFM results. In electrical resistivity measurement, show the resistivity of all the samples decreases as the film thickness or grain size increases, but the trend inverts for the film with 7 coatings and the maximum MR with the value of 21.35 %, in Hexagonal structure.

Abstract: We investigate the effects of Cr, Ru and Sn substitution on electrical resistivity and magnetoresistance property of polycrystalline samples La_0.67Sr_0.33Mn_1-xB_xO₃ (x = 0, 0.05; B= Ru, Cr and Sn) compounds. The value of M-I transition temperature (T_P) decreases while resistivity increases with Cr, Ru and Sn substitution, moreover, the largest low-temperature magnetoresistance (MR %) is found at magnetic field dependent (Isotherm), which suggest that the spin-dependent scattering from internal grain regions is also responsible for the low-temperature MR %. Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of various transition metals in the Mn-site leads to a decrease in conductivity of the doped manganite samples, with conduction being controlled by the disorder induced localization of charge carriers.

Abstract: Since ZnO is a wide band gap (3.37 eV) semiconductor with a large exitonic binding energy (60 meV), it has been considered as a candidate for various applications, such as ultraviolet (UV) light emitting diodes and laser diodes. For the applications of ZnO-based optoelectronic devices, it is necessary to produce n and p type ZnO films with the high quality. Since ZnO is naturally n-type semiconductor material due to intrinsic defects, such as oxygen vacancies, zinc interstitials, etc., it is easy to produce n-type ZnO with high quality. However, it is difficult to produce low-resistive and stable p-type ZnO due to its asymmetric doping limitations and the self-compensation effects of the intrinsic defects. According to the theoretical studies, p-type ZnO can be realized using group-V dopants substituting for O, such as N, P and As. Among them, N has been suggested to be an effective acceptor dopant candidate to achieve p-type ZnO, because that nitrogen has a much smaller ionic size than P and As and the energy level of substitutional N_O is lower than that of substitutional P_O and As_O. Transparent p-type ZnO: N thin films have been fabricated using the pulsed laser deposition method at deposition temperatures 800 °C under the O₂ and N₂ mixing pressure 6Pa. N-doped ZnO films were deposited on sapphire substrate using metallic zinc (99.999%) as target. The structural, optical and electrical properties of the films were examined by XRD, UV-visit spectra and Hall effect measurement. We found that thin film contain the hexagonal ZnO structure. The Hall effect measurement revealed that the carrier concentration is 5.84×10¹⁸ 1/ cm³, and Hall mobility is 0.26 cm^2/Vs, electrical resistivity is 4.12ohm-cm. Film thickness is 180nm. Besides, Visible light transmittance is more than 80%, and calculative band-gap is 3.1 eV, which is lower than ZnO.

Abstract: We successfully deposited the purely c-axis oriented Fete thin film, which shows superconducting transition in electrical resistivity about 12 K, by using pulsed laser deposition method. The electrical transport measurements of the thin film are studied with magnetic fields up to 14.0 T. thermally activated energy is analyzed using simple conventional Arrhenius relation and more precise relation who is closer to experimental results. Besides, the upper critical magnetic field and the vortex glass transition temperatures for the Fete thin film are studied.

Abstract: The compound Dy₂Si₂O₇ exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy₂Si₂O₇ are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (T_o) and density of states at fermi level are obtained. The ac conductivity σ_ac (ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σ_ac (ω) =B ω ^s , where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

Abstract: The structural and electrical transport properties of La0.67Ba0.33Mn1-yTiyO3 manganite, with y = 0.00, 0.05, 0.10, 0.15, 0.20, 0.40 and 0.60, prepared using the solid state reaction technique have been investigated. The X-ray diffraction spectra of the Ti substituted samples showed the formation of single phase compound with Pm3m cubic structure except for the y = 0.60 sample, which showed La2Ti2O7 phase formation. Lattice parameter increased with Ti content and then decreased at y = 0.60. Resistivity versus temperature study showed that only samples with y = 0.05 and 0.10 exhibited both metallic and semiconductor-like behaviour with the metal-insulator transition temperature, Tp of 167 K and 43 K, respectively. At higher Ti concentration the samples only showed the semiconducting behaviour. At T < Tp the resistivity curves followed the ρ = ρo1 + ρ1T2 relation and for T > Tp, the curves can be fitted with the nearest neighbour hopping (NNH), variable range hopping (VRH) or/and the small polaron hopping (SPH) models.