DC Electrical Resistivity Studies Research Articles

Effect of rare earth (Sm3+) substitution in mixed Ni-Zn-Co ferrites: Structural, magnetic, and DC electrical resistivity studies

NiZnCo ferrite has good magnetic properties and is one of the core materials used in magnetic devices. The solid-state reaction approach is utilized to synthesize Ni0.4Zn0.35Co0.25Fe2-xSmxO4 (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) ferrites for investigation of structural, morphological, functional, magnetic and electrical resistivity properties using various characterization techniques. The techniques used for characterization were XRD, SEM, FTIR, VSM, and DC electrical resistivity. XRD spectra were used to determine phase confirmation, cubic crystallite size, andtheir variation with dopant content. No additional phase or impurity was found. The SEM pictures revealed ahomogeneous spherical particle formation with minimal porosity. With absorption bands under 1000 cm−1, FTIR spectra indicate the formation of a spinel structure. Tetrahedral (580 to 599 cm−1) and octahedral (388 to 399 cm−1) bond changes can be seen in infrared spectra. The magnetic hysteresis curves revealed soft ferromagnetic behavior, with coercivity (Oe) (532.13 to 312.10Oe) rising and saturation magnetization (Ms) (83.51 to 60.75 emu/g) falling as doping concentration increased. The DC electrical resistivity of synthesized nanoparticles with various compositions was measured against higher temperatures to confirm their semiconductor nature. The findings demonstrated the typical decreasing trend with rising temperature.

Phase transformation, morphology, DC electrical resistivity and dielectric properties investigations of properties of manganese doped barium titanate nanoparticles

In this work, manganese (Mn) doped barium titanate BaTi1-xMnxO3 nanoparticles with varying composition of Mn (x = 0.0, 0.10 and 0.20) were prepared by using sol–gel self-ignition wet chemical route. The influence of Mn doping on crystal structure, infra-red, morphology, DC electrical resistivity and frequency dependent dielectric studies was systematically investigated. To know the crystalline nature and purity of the prepared samples, a non-destructive X-ray diffraction (XRD) tool was used. The analysis of XRD results revealed that pure BaTiO3 and BaTi1-xMnxO3 with x = 0.1, samples show tetragonal structure and for higher Mn content (x = 0.20) shows the hexagonal structure. The values of interplanar spacing, Miller indices, etc. were used to determine the unit cell parameters, X-ray density and unit cell volume. The highest intensity peak (110) observed in XRD pattern was considered to determine the crystalline size and which is found to be in the range of 3 to 8 nm. Scanning electron microscopy (SEM) technique was employed to study the surface morphology. SEM analysis confirm the dense nature of the grains with hexagonal shape for x = 0.2. EDX results confirm the presence of Ba, Ti, Mn and O elements as per the stoichiometric proportion. The functional groups and chemical bonds of Mn doped BaTiO3 were obtained by Fourier transform infrared spectroscopy (FTIR). The temperature dependant DC electrical resistivity studies were performed by standard two probe technique. The conductivity plot exhibits negative temperature coefficient (NTC). The activation energy and resistivity both decreased with Mn doping. The dielectric properties such as dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tan δ) were studied by means of LCR-Q meter. The variation of these parameters as a function of frequency shows the exponential decrease. The dielectric constant and dielectric loss reduces, whereas dielectric loss tangent increase on Mn doping. The ac conductivity increases with frequency.

Silver concentration effects on structural and electrical properties of La0.4Pr0.25Ca0.35-x Ag x MnO3 manganite elaborated by sol–gel method

ABSTRACT La0.4Pr0.25Ca0.35-x Ag x MnO3 samples were elaborated using sol–gel method. X-ray diffraction study indicates that the investigated compounds exhibit an orthorhombic structure with Pbnm space-group symmetry. Introducing Ag in the investigated system leads to changes in the unit cell parameters and cell volume. The electrical properties have been investigated using the impedance spectroscopy technique. Dc-electrical resistivity study shows a metal-semiconductor transition at T MS = 220 K, which is Ag independent. Also, it is found that the resistivity decreases with increasing silver content. Then, the activation energy of the hopping mechanism is reduced with increasing Ag concentration. For different silver concentration, the conduction is dominated by thermally activated small polaron hopping (SPH) process at the high temperature and by variable range hopping (VRH) process at lower temperatures.

Structural, Magnetic and DC Electrical Resistivity Studies of Ni–Zn–Cr Ferrites Prepared by the Citrate-Gel Auto-Combustion Method

Nanocrystalline chromium substituted Ni–Zn nanoferrites with composition Ni0.5Zn0.5CrxFe2−xO4 (0 ≤ x ≤ 0.25, in steps of 0.05) have been synthesized using citrate-gel auto-combustion method. The as synthesized powder of the starting composition has been characterized by using TG–DTA in air atmosphere for the temperature up to 800 °C and X-ray diffraction for its structure. Upon confirming the spinel phase for the starting composition, the chromium substituted Ni–Zn ferrite nano powders were synthesized by the similar procedure. The as synthesized powders were pressed into pellets and toroids under uniaxial pressure followed with sintering in air atmosphere for 4 h at 1100 °C for electrical and magnetic characterizations. The X-ray diffraction studies revealed a decrease of the lattice constant and considerable modification in the structure of Ni–Zn ferrite with the substitution of Cr3+ for Fe3+ ions. The room temperature FT-IR spectra displayed three significant IR absorption bands in the wave number range of 350–600 cm−1 which is a characteristic of the spinel structure. The band positions and intensities were found to vary with chromium substitution in Ni–Zn ferrite. The room temperature DC electrical resistivity and activation energy for conduction in the Ni–Zn–Cr ferrite samples were measured by using the two-probe method while the AC resistivity studies were carried out in the frequency range of 1 kHz to 13 MHz and the all the observations have been discussed in the light of existing understanding.

Effect of fractional substitution of Sb3+ ions on structural, magnetic and electrical properties of cobalt ferrite

The present work suggests the preparation of a series of Sb-substituted cobalt ferrite by the sol–gel auto-combustion method. The phase purity of the samples was evaluated by X-ray diffraction, Raman analysis, and infrared spectroscopy. Raman and infrared spectra exhibited the characteristic absorption bands corresponding to M-O stretching vibrations. The precise chemical composition was verified using the Inductively coupled plasma – atomic emission spectroscopy technique. X-ray photoelectron spectroscopy studies validated the chemical state of present species of the metal ions. The morphology of the samples and their particle sizes were estimated by Scanning electron microscopy and Transmission electron microscopy analysis, respectively. The saturation magnetization decreased with Sb-substitution both at 300 K and 50 K and showed a comparatively higher value at 50 K. The DC electrical resistivity studies showed the semiconducting behavior of the materials and an increasing trend observed with Sb3+ ions content. The increase in dielectric constant with increasing Sb3+ ions concentration and the temperature was observed.

Influence of Al–Cr co-substitution on physical properties of strontium hexaferrite nanoparticles synthesized by sol–gel auto combustion method

Substituted strontium hexaferrite ceramics SrCr x Al x Fe12−2x O19 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were prepared by sol–gel auto-combustion method. X-ray diffraction (XRD) study revealed the M-type hexagonal structure of the synthesized nanoferrites with some additional peaks of Fe2O3. The lattice constants (a and c), unit cell volume (V), X-ray density (ρ x ), bulk density (ρ m ), porosity (P) and average crystallite size (t) values changes when Al–Cr ions are co-substituted in SrFe12O19 lattice, resulting in the structural variation. The surface morphology of the grains was examined by scanning electron microscopy (FESEM). Fourier transform infrared spectroscopy (FTIR) confirmed the formation of hexagonal ferrite structure. Ferromagnetic nature confirmed by recording M-H curves exhibited typical hysteresis loop at room temperature using pulse field hysteresis loop tracer technique. The large coercivity (H c ) values indicate the nanocrystalline nature of the present samples. The coercivity (H c ), saturation magnetization (M s ), remanence magnetization (M r ) and magneton number (n B ) decreases with increase in Al–Cr content x. The DC electrical resistivity studies of the prepared samples were carried out in the temperature range of 300–873 K using a standard two-probe technique. Curie temperature (Tc) i.e. ferrimagnetic to paramagnetic transition temperature for all samples was obtained from resistivity data. The Curie temperature decreases linearly as the concentration of Al–Cr content is increased. The activation energy below and above Tc was calculated. The dielectric parameters such as dielectric constant (ɛ′), dielectric loss (ɛ″) and loss tangent (tan δ) were measured in the frequency range 50 Hz–5 MHz at room temperature. All the dielectrical parameters show compositional as a function of frequency dependences. At lower frequencies, it is observed that the dielectric constant (ɛ′), dielectric loss (ɛ″) and loss tangent (tan δ) are high.

Electrical and Dielectrical Properties of Low-Temperature-Synthesized Nanocrystalline Mg2+-Substituted Cobalt Spinel Ferrite

Nanocrystalline samples of Co 1−x Mg x Fe 2 O 4 (x = 0.0, 0.25, 0.50, 0.75, and 1.0) ferrite were synthesized by wet chemical sol-gel auto combustion method. The spinel cubic phase formation of Co 1−x Mg x Fe 2 O 4 ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg planes observed in XRD pattern belong to the cubic spinel structure of ferrite. The microstructural studies were investigated through scanning electron microscopy (SEM) technique. Pellets of Co–Mg ferrite were used to study the electrical and dielectric properties. The DC electrical resistivity studies of the prepared Co 1−x Mg x Fe 2 O 4 (x = 0.0–1.0) ferrite samples were carried out in the temperature range of 300–873 K using a standard two-probe method. Ferrimagnetic to paramagnetic transition temperature known as Curie temperature (T c) for all samples was noted from resistivity data. The Curie temperature decreases linearly as concentration of magnesium content is increased. The activation energy below and above T c was calculated. The dielectric parameters such as dielectric constant $(\varepsilon ^{\prime })$ , dielectric loss $(\varepsilon ^{\prime \prime })$ , and loss tangent (tan δ) were measured with frequency at room temperature in the frequency range 10 kHz to 1 MHz. The dielectric constant $(\varepsilon ^{\prime })$ measurements with increasing frequency show two peaks at room temperature of measurements for all samples under investigation. The peaks observed show compositional dependences as a function of frequency. The observed behavior in the electrical and dielectric behavior of nanocrystalline Co 1−x Mg x Fe 2 O 4 spinel ferrites is discussed in this work.

DC electrical resistivity studies and structure of Ni0.5Zn0.5CrxFe2-xO4 nanoferrites

Chromium substituted Ni – Zn nano ferrite samples with composition Ni 0.5 Zn 0.5 Cr x⋅ Fe 2-x O 4 (x = 0.00 to 0.25 in steps of 0.05) have been prepared by autocombustion method employing citric acid as an oxidant. Structural, morphological and microstructural characterizations were done on the sintered powders at 1000°C while the DC electrical resistivity studies have been performed on the pellets sintered at the same temperature. The thermogravimetric and differential thermal analysis (TG-DTA) studies indicated the presence of broad exotherm and valley centered about temperature of 400°C. The formation of single-spinel phase has been observed for all the samples. The ionic packing coefficient, vacancy parameter and fulfillment coefficient have all been obtained for each composition. The scanning electron micrographs showed the formation of fine grains with size very less than 1 μm in all samples with a little agglomeration. The observed variation in DC electrical resistivity and activation energy with Cr 3+ substitution are attributed to the modifications in microstructure, structural defects and the influence of Cr 3+ ions with support of hopping mechanism.

Effect of exceeding the concentration limit of solubility of silver in perovskites on the dielectric and electric properties of half doped lanthanum–calcium manganite

Dielectric and electric properties of La0.5Ca0.2Ag0.3MnO3 (LCMO–Ag) manganite have been investigated using admittance spectroscopy technique. AC conductivity analysis shows that the conductivity verifies the Jonscher universal power law. The deduced exponent ‘s’ values prove that hopping model is the dominating mechanism in the material. From dc-electrical resistivity study, conduction process is found to be dominated by thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of relaxation phenomenon and allows to modelize the sample in terms of an electrical equivalent circuit. Also, impedance study confirms the contribution of grain boundary in the electrical properties. Dielectric studies indicate that the La0.5Ca0.2Ag0.3MnO3 compound has a Debye-like relaxation. The temperature dependence of permittivity is well fitted by the modified Curie–Weiss law. It is found that dielectric permittivity behavior and the estimated relaxation parameter value (γ≈2), support the evidence of the relaxor nature of La0.5Ca0.2Ag0.3MnO3 material. The high dielectric constant and the low loss tangent indicate the material is promising for tunable capacitor applications.

Magnetic properties and DC electrical resistivity studies on cadmium substituted nickel–zinc ferrite system

Polycrystalline Ni0.65−xCdxZn0.35Fe2O4 ferrites with x varying from 0.00 to 0.20 in steps of 0.04 have been prepared by conventional ceramic route. Calcination and sintering of samples were performed at 950 and 1250°C for 4 and 2h, respectively. The prepared samples were characterized by powder X-ray diffraction. The observed modifications in structure and increase in lattice constant are attributed to the difference in ionic radius of substituted Cd2+ ion and displaced Ni2+ ion. The room temperature specific saturation magnetization and Curie temperature are observed to decrease continuously with decrease in cadmium content and are attributed to the decline of A–B exchange interaction. The monotonic increase in initial permeability and decrease in magnetic loss are observed with cadmium concentration. An increase in dc electrical resistivity is observed up to x=0.12 of cadmium followed by a continuous decrease. The variation of electrical resistivity with temperature was measured in the temperature range of RT–140°C and the corresponding activation energies for conduction obtained from the logρ vs 1/T graphs.

Physical and Electrical Properties of Nanosized Mn‐ and Cr‐Doped Strontium Y‐Type Hexagonal Ferrites

Nanometer‐sized crystallites of Y‐type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn‐ and Cr‐doped derivatives have been synthesized by the sol–gel method. Y‐type phase formation was achieved at a considerably lower temperature of 950°C than is required in the traditional solid‐state method (1200°C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2−xMnx Fe12O22 (x=0.0–2.0), and chromium at octahedral site, Sr2Ni2 Fe12−yCryO22 (y=0.0–1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13–45 nm is calculated from the X‐ray diffraction data. The energy‐dispersive X‐ray fluorescence analysis shows that Y‐type hexaferrites can be prepared with a base of strontium. The extent of doped Cr+3 ions at the octahedral site has been increased from the reported maximum value of y=1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr‐doped samples have comparatively higher resistivity than Mn‐doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 × 109Ω‐cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples.

Transparent and low resistive nanostructured laser ablated tungsten oxide thin films by nitrogen doping: I. Nitrogen pressure

Nitrogen incorporated tungsten oxide films are deposited on heated quartz substrates (973 K) for various nitrogen background pressures (namely, pN2 = 0.04, 0.08, 0.12, 0.17 and 0.20 mbar) by the pulsed laser deposition technique. The prepared films are characterized by using techniques such as x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), atomic force microscopy (AFM), scanning electron microscopy, micro-Raman spectroscopy, UV–visible spectroscopy and temperature dependent dc electrical resistivity studies. XRD measurements revealed the presence of tungsten sub-oxide and WO3 phases depending on the nitrogen ambient pressure. Nitrogen incorporation in the films is confirmed through EDX analysis. Morphological features consisting of densely packed, void-free grains with a distinct grain boundary are portrayed through the AFM images of the films. The WO3 lattice distortion due to nitrogen incorporation is discussed using micro-Raman spectra of the films. Band gap narrowing, moderate transmittance in the visible range and the very low resistivity exhibited by the films prepared at pN2 = 0.12 mbar are imperative as far as solar cell applications are considered. A comparably higher visible transmittance with a band gap of 3.141 eV and a low resistivity obtained for the N : WO3 films prepared at a nitrogen ambient of 0.17 mbar is among the best reported for the coexistence of transparency in the visible range and conductivity in tungsten oxide films, which make them significant for micro-electronic applications.

Solid state studies on Bi 1.7− xHg xV 8O 16 ( x ≤ 0.4) and magnetic properties of alkali metal inserted A xBi 1.7V 8O 16 (A = Li and Na) hollandite type phases

The effect of substitution of ‘Hg’ at the Bi-site in Bi 1.7V 8O 16 on the phase formation and electrical properties has been studied. In Bi 1.7− x Hg x V 8O 16, single phase formation is achieved only for x ≤ 0.4 and all the phases crystallize in tetragonal structure. The dc electrical resistivity studies indicate that all the mercury substituted single phase compounds Bi 1.7− x Hg x V 8O 16 are electrically semiconducting and the room temperature resistivity values increase with increasing mercury content. Alkali metals like lithium and sodium have been inserted successfully into the tunnels of Bi 1.7V 8O 16. The lithium intercalated phase Li 2.7Bi 1.7V 8O 16 shows antiferromagnetic ordering, whereas the sodium intercalated phase NaBi 1.7V 8O 16 exhibits Pauli paramagnetic like behavior down to 4.5 K.

Mössbauer and DC electrical resistivity study of Zn substituted tetragonal CuFe 2− yGa yO 4 compound

Mössbauer technique has been employed for the study of hyperfine parameters of the compound Cu 1− x Zn x Ga y Fe 2− y O 4 with x from 0.0 to 0.5, and y=0.3 in order to determine the cation inter-site distribution and establish the conduction mechanism. Substitution of Ga 3+ and Zn 2+ ions results in a decrease of the hyperfine field at octahedral B-sites as well as tetrahedral A-sites. The area ratio of Fe 3+ ions at A- and B-sites at 77 K indicates that Zn 2+ ions occupy the tetrahedral A-site where, Cu 2+, and Ga 3+ ions occupy the octahedral B-site. DC electrical resistivity measurements carried out on the studied samples indicate a semiconducting behavior. The magnetic transition temperature T c determined from the relation of resistivity ( ρ) with temperature was found to decrease linearly with increasing Zn content. The activation energies calculated at the magnetic and paramagnetic regions are found to increase with increasing Zn content. The obtained results for the Mössbauer parameters are interpreted based on the superexchange and supertransferred hyperfine interactions, where results of resistivity are explained in light of the hopping conduction occurring at the octahedral B-sites.

X-ray, IR and dc electrical resistivity study of CaCl2-doped zinc–copper ferrite system

Polycrystalline soft ferrites, ZnxCu1–xFe2O4 (x = 0.30, 0.50, 0.70, 0.80 and 0.90), doped with controlled amounts of calcium chloride (CaCl2) were prepared by standard ceramic techniques. The samples were characterized using X-ray and IR techniques. These compounds are being developed as humidity sensing materials with a final aim of developing a sensor. The temperature dependence of the dc resistivity (ρ) was studied by the usual two-probe method from room temperature to 500 °C. Parameters such as resistivity (ρ) and activation energy (ΔE) were computed and the results discussed on the basis of existing theories.

Structural and dc electrical resistivity study of Nd3+ substituted Zn-Mg ferrites

Structural and dc electrical resistivity study of Nd3+ substituted Zn-Mg ferrites

Structural and dc electrical resistivity study of Gd 3+-substituted Cu-Cd mixed ferrites

Polycrystalline ferrite compositions of Cd x Cu 1- x Fe 2- y Gd y O 4 ( x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0; y = 0.0 and 0.1) were prepared by the standard ceramic technique. The X-ray crystallographic study was done using filtered Cu K α radiation. From the diffractograms it is observed that for x ⩾ 0.2 compounds are cubic spinels, while for x = 0 they are tetragonal, and the dependence of the lattice constant on cadmium concentration obeys Vegard's law. The infrared absorption of the powder samples shows two strong absorption bands in the frequency range 400–600 cm -1, and the analysis shows that Gd occupies ‘B’ sites. The chemical analysis was done by atomic absorption spectroscopy. The dc resistivity study shows an increase in Δ E values and thus in the resistivity after Gd 3+ substitution, suggesting that even though Gd 3+ occupies ‘B’ sites it does not take part in the conduction mechanism, but impedes it.

Evaluation of Geothermal Potential of Truth or Consequences Area, New Mexico: ABSTRACT

Truth or Consequences, New Mexico, is the site of a known thermal anomaly with free-flowing artesian wells and springs ranging in temperature from 36.7 to 45.6°C. Recently completed electrical resistivity surveys and hydrogeologic studies indicate two specific areas worthy of further evaluation for low to moderate-temperature geothermal potential: one area about 1 km northwest of Truth or Consequences, and the other at the southwestern end of the Mud Springs Mountains. The DC electrical resistivity study consisted of three Schlumberger vertical electric soundings and an extensive roving bipole-dipole survey in the vicinity of the previously mentioned target areas. Three total-field apparent resistivity maps were generated from the data collected during the roving bip le-dipole survey. To demonstrate the effect of lateral heterogeneities in the geothermal reservoir zone, these maps were compared with theoretical total-field maps computed for a one-dimensional layered earth. Combined electric, hydrologic, and lithologic data indicate that the major thermal aquifer is a fault-bounded block of Pennsylvanian limestone with a major recharge area in the Mud Springs Mountains. This carbonate aquifer is approximately 1 km thick and, locally buried as much as 120 m beneath Quaternary alluvium and the nonthermal piedmont aquifer. Transport of thermal waters from the carbonate aquifer into the Rio Grande flood-plain aquifer occurs along a N60°W-trending reverse fault zone which dips 60°N. Latest movement along this fault zone has tentatively been dated as middle to late Pleistocene. The heat source for the thermal aquifer may be related to early Pleistocene igneous activity. End_of_Article - Last_Page 564------------