Electrical Properties Of La0 Research Articles

Effect of synthesis route on structural, morphological, Raman, dielectric, and electric properties of La0.8Ba0.1Bi0.1FeO3

Two compounds with the formula La0.8Ba0.1Bi0.1FeO3 have been prepared by the sol–gel (LBBFO-SG) and the auto-combustion (LBBFO-AC) preparation methods. The effect of the preparation method on structural, morphology, vibrational, electrical, and dielectric properties have been carried out using the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Raman and impedance spectroscopy. The Rietveld refinement of the XRD diffractograms confirms the crystallization of both compounds through the Pnma space group. Furthermore, the nano-size scale of the prepared compounds was verified by the XRD and the SEM microscopy. From the Raman study, we conclude that the vibration modes are similar to those of the pure LaFeO3 with a slight shape change in some modes. The relaxation processes were analyzed with the Bergmann formalism to validate the presence of two relaxation processes corresponding to grains and boundary grains contributions. These relaxations have been confirmed by studying the dielectric constant also the dielectric loss tangent is used to study the ferroelectric–paraelectric phase transition at around room temperature. The activation energy for both contributions has been calculated from the impedance, the modulus, and the dielectric loss tangent and they have almost the same values. The Nyquist plots (Z″ vs. Z′) have been adjusted using two circuits in series containing each one a resistance in parallel to a CEP capacitance.

Enhanced electrical properties of La1.9Nd0.1Ti2O7 ceramics

La2−xNdxTi2O7 (LNTO) ceramics with enhanced electrical properties have been prepared by traditional solid-state reaction method. The LNTO ceramics maintain a pure monoclinic phase at x ≤ 0.1. At x > 0.1, an orthorhombic phase Nd0.95TiO3 appears. Impedance spectra indicates that the substitution of La3+ ions by Nd3+ ions at A sites generates defects, resulting in the enhanced distortions of TiO6 octahedrons. The dielectric relaxation activation energy for these defects is 1.2 eV in temperature range T ≥ 650 ℃. The conductance activation energies are 0.3 eV and 1.0 eV for impure ions/thermions and defects/oxygen vacancies, respectively. The contributions of impure ions/thermions and defects/oxygen vacancies have been distinguished through the analysis of both normalized imaginary impedance Z″ and electrical modulus M″. Their impedance relaxation activation energies in normalized Z″ spectra are 1.3 eV and 0.8 eV, respectively. An enhanced piezoelectric coefficient (d33 = 2.8 pC/N) appears in La1.9Nd0.1Ti2O7 (LNTO-0.1) ceramics.

The effect of particle size on the structural, magnetic and electrical properties of La0.9Ba0.1MNO3 manganite samples

ABSTRACTIn this work, the magnetic and transport properties of micro and nanometer-sized samples of La0.9Ba0.1MnO3 manganite have been studied. The temperature variation of ac susceptibility of the nanometer-sized sample shows one transition at high temperature (265 K). On the contrary, the ac susceptibility of the micrometer-sized sample shows two transitions with a high-temperature transition occurring at 240 K and low-temperature transition around 100 K. The high-temperature transition corresponds to the paramagnetic-ferromagnetic (PM–FM) transition (Tc) and is independent of frequency, while the low-temperature transition is frequency-dependent and shifts toward high temperatures by increasing frequency. The different magnetic behavior for two samples may be understood on the basis of crystalline homogeneity. The competition between FM double exchange and antiferromagnetic superexchange component in the micrometer-sized sample leads to the cluster glass state at low temperatures. The magnetotransport data further supports the obtained results from magnetic measurements.

Electric field control of the photoinduced resistance increase in La0.7Sr0.3MnO3/LaTiO3/SrTiO3 heterostructure

In this work we have studied the effect of light and electric field on the electrical properties of La0.7Sr0.3MnO3 (LSMO) film at 300 K. Taking advantage of it's charge, spin, orbital and lattice degrees of freedom, we have successfully shown that light and electric field together can be used to tune the resistance states of the manganite system. Using applied gate voltage (Vg) and light we were able to obtain a change in resistance of about +/-7.5%. Furthermore, incorporating an ultra thin interfacial LaTiO3 (LTO) layer provides valuable insight on the origin of the photoinduced effect. The observed photoinduced effect is attributed to photoexcited down spin eg electrons, interfacial charge injection and manipulation of orbital occupancy depending on the gate voltage and wavelength of light.

Impact of Ag doping on the structural, surface morphologic and electrical properties of La0.625(Ca0.285Sr0.09)MnO3 polycrystalline ceramics

In this study, Ag-doped La0.625(Ca0.285Sr0.09)MnO3:Agz (LCSMO:Agz, z = 0, 0.1, 0.2, 0.3, and 0.4) polycrystalline ceramics were prepared by sol-gel method, then characterized by various techniques. X-ray diffraction (XRD) showed that all bulk prepared specimens crystalized in LCSMO phase with orthogonal cubic structure (space group of Pnma) and without impurities. Scanning electron microscopy (SEM) revealed good compactness with fewer holes. Average grain sizes and quantity of grain boundaries (GBs) correlated with Ag doping amounts. As z content rose, resistivity dropped, and both peaks temperature coefficient of resistance (TCR) and magnetoresistance (MR) first increased and then decreased. Several previous studies indicated that Ag doping amount could affect TCR and MR peaks. At z = 0.3, TCR peaks reached maxima of 10.27% (289.56 K), at z = 0.1, MR peaks reached maxima of 15.63% (293.08 K). As z increased from 0 to 0.4, the temperature of peak TCR (Tk) was adjusted to room temperature from 289.56 to 294.22 K. TCR peak of La0.625(Ca0.285Sr0.09)MnO3:Agz material was improved at room temperature when compared to values reported in the literature. This could be related to changes in tolerance factor (τ) and average A-site cationic radius (rA). Overall, LCSMO:Agz ceramics look promising for infrared detectors and colossal magnetoresistance (CMR) radiant heating instruments at room temperature.

Effect of V Substitution on the Electrical Properties of La0.5Sr0.5Co1−xVxO3 (x = 0.00–0.10) Ceramics

In this paper, the microstructures, resistivity as well as temperature coefficient of resistance (TCR) of La0.5Sr0.5Co1−xVxO3 (x = 0.00–0.10) ceramics were studied. These ceramic samples were prepared through conventional solid-state reaction method. Results showed that the substitution of Co ions with V ions improved the densification level of ceramic samples and changed their resistive characteristics accordingly. A uniform microstructure of La0.5Sr0.5 Co1−xVxO3 ceramic was realized at x = 0.05 when sintered at 1100°C. The resistivity of ceramics increased slightly as the V content varied in the range of 0.00–0.10. The TCR value of all tested samples was maintained between +1304.35 ppm/°C and +2958.26 ppm/°C. A low resistivity value of 0.38 mΩ cm and the minimum TCR value of +1304.35 ppm/°C were achieved as x = 0.05 in La0.5Sr0.5Co1−xVxO3. It was found that the substitution of Co ions with V ions facilitated lowering the TCR value without changing the resistivity too much. Thus, these ceramics are promising materials for conductive oxide used in thick-film resistors.

Physical properties of double-doping Lanthanum manganite for bolometer applications

We have studied the structural, magnetic, critical behavior and electrical properties of La0.5Ag0.1Ca0.4MnO3 sample synthesized by traditional Solid State route. X-ray diffraction studies reveal that La0.5Ag0.1Ca0.4MnO3 crystallizes in the orthorhombic structure with Pnma space group. Vibrational study by means of infrared spectroscopy each give a part of the vibrational reality of the material explored. Studying the magnetic and electric properties of La0.5Ag0.1Ca0.4MnO3, it has been found the compound exhibits a second-order phase transition around the ferromagnetic-paramagnetic transition. The critical behavior of La0.5Ag0.1Ca0.4MnO3 compound is investigated based on the data of static magnetic measurements in the vicinity of its critical temperature TC. The estimated critical exponents derived from the magnetic data were estimated using modified Arrott plot (MAP) and critical isotherm technique (CI). The critical exponents find are comparable to the values theoretical predicted for the values corresponding to the 3D-Ising model and are confirmed by scaling equations of state. The investigated compound exhibits a semiconductor-metal transition at 380 K. For the important value of TCR at zero magnetic fields, we consider our sample is a good candidate infrared sensor for night vision bolometer applications.

Thermal and Electrical Properties of Highly Dense Ceramic Materials Based on Co-doped LaYO3

Solid oxide electrolytes showing proton transport are extensively studied materials, which can be utilised in different types of highly efficient energy systems such as solid oxide fuel cells, solid oxide electrolysis cells, membrane converters and sensors. Here we present the results of a study of the functional properties of LaYO3-based materials, which exhibit higher chemical stability than the more well known proton-conducting electrolytes, cerates and zirconates of alkaline earth elements. The structural, ceramic, thermal and electrical properties of La0.9Sr0.1YO3–δ have been thoroughly studied depending on the partial Y substitution with some lanthanides (10 mol.% of Yb, Dy, Ho). According to the experimental data, La0.9Sr0.1Y0.9Yb0.1O3−δ can be considered a promising alternative to the basic oxide because of its better transport properties and the fact that there are no detrimental changes in other functional characteristics.

Structural and electrical properties of La0.67(Ca0.3Sr0.03)MnO3 composites prepared with added Ag

In this account, La0.67(Ca0.3Sr0.03)MnO3:mol%Agx (LCSMO:Agx, 0 ≤ x ≤ 0.5) high-density composites were successfully prepared by the conventional sol-gel method using deionized water as solvent. The structures, surface morphologies and electrical transport properties of obtained composites were analyzed by various analytical methods. The X-ray diffraction (XRD) profiles of LCSMO:Agx exhibited single perovskite structure with pure orthorhombic crystal structure (Pnma space group) and without presence of traces secondary phases. Field emission scanning electron microscopy (FESEM), XRD and X-ray photoemission spectroscopy (XPS) depicted good grain surface connectivity of the specimens. In addition, grain size increased with Ag doping. The influences of Ag2O doping on materials electrical properties were also explored. The results indicated the presence of silver as Ag+ ions substituting A-site ions. Furthermore, small amounts of metallic silver gathered at the grain boundaries (GBs) were detected. This increased both the MnO bond length and MnOMn bond angle, and slightly expanded both cell volume (V) and lattice constant (a, b, c). The maximum value of temperature coefficient of resistivity (TCR) reached 11.2% K−1 with peak TCR temperature (Tk) of 281.5 K. The improved electrical transport performances of LCSMO:Agx materials were attributed to Ag doping, which enhanced Mn4+ ion amounts and GBs connectivity in each specimen. In addition, excess replacement of A-site ions by Ag+ expanded the metal-insulator transition characteristics and reduced the temperature coefficient of resistivity. Finally, a double exchange based mechanism was proposed to explain the above results.

Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 Ceramics

The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.

Enhancement of grain growth and electrical conductivity of La0.8Sr0.2MnO3 ceramics by microwave irradiation

We studied crystallization, grain growth and electric properties of La0.8Sr0.2MnO3 (LSM) ceramics which were produced using the microwave-treatment. While co-precipitated nanoparticles remain mainly amorphous, the microwave irradiated particles are crystallized into LSM and La2Mn2O7 at 550 °C, due to higher dielectric polarizability of La. This, in turn, decreases the amount of the second phase La2O3 in calcined powder and promotes the growth of perovskite grains during sintering at 1400 °C. Larger grains of LSM ceramics lower the activation energy of small polaron hopping from 0.35 eV to 0.24 eV and increases high-temperature electric conductivity. In addition, high crystallinity of LSM ceramics from the microwave-treatment suppresses a chemical reaction with ZrO2 and NiO in a temperature range of 900 – 1100 °C under oxidizing and reducing ambiances. These results show that LSM ceramics from the microwave-assisted reaction meet requirements for an interconnect layer for solid oxide electrolysis cells.

Acceptor-doped La1.9M0.1Ce2O7 (M = Nd, Sm, Dy, Y, In) proton ceramics and in-situ formed electron-blocking layer for solid oxide fuel cells applications

In the present work, La1.9M0.1Ce2O7 (M = Nd, Sm, Dy, Y, In) powders are synthesized by citric acid-nitrate sol-gel combustion method. The effects of the acceptor dopant on the phase structure, microstructure and electrical properties of La1.9M0.1Ce2O7 ceramics are investigated. All La1.9M0.1Ce2O7 ceramics possess a single-phase fluorite structure. It turns out that the In-doped ceramic exhibits the highest electrical conductivity of 0.82 × 10−2 and 2.03 × 10−2 S cm−1 at 700 °C both in dry air and wet 5% H2Ar atmospheres, respectively. Furthermore, in order to eliminate the internal short circuit resulting from the reduction of Ce4+ to Ce3+, a novel NiBaCe0.5Zr0.3Dy0.2O3-δ composite is applied and evaluated as the anode for the fuel cell based on La1.9In0.1Ce2O7 electrolyte. Raman and scanning electron microscope and energy dispersive spectrometer analyses indicate that a Ba-containing electron-blocking layer is formed in-situ at the anode/electrolyte interface. The new structured fuel cell with NiBaCe0.5Zr0.3Dy0.2O3-δ anode and La1.9In0.1Ce2O7 electrolyte exhibit significantly improved open circuit voltage of 1.005 V along with maximum power density of 546 mW cm−2 at 700 °C using humidified hydrogen fuel. The results demonstrate that La1.9In0.1Ce2O7 electrolyte and NiBaCe0.5Zr0.3Dy0.2O3-δ anode can be considered as the promising candidates for solid oxide fuel cells applications.

Correlation between magnetic and electrical properties of La0.6Sr0.4Mn0.9V0.1O3 based on critical behavior

ABSTRACTThe electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic isolant regions. So, we found that the estimated results are in adequate accordance with experimental data. The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La0.6Sr0.4Mn0.9V0.1O3 resistivity. The estimated critical exponents are (β = 0.326 ± 0.01; γ=1.237 ± 0.02 and α = 0.112). The values of these exponents obtained from resistivity are very close to them predicted by the 3D-Ising model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The obtained values of the temperature coefficient of resistance (TCR) for La0.6Sr0.4Mn0.9V0.1O3 sample is comparable with some systems used for infrared sensors.

An investigation on the microstructural and electrical properties of La0.85DxSr0.15–xGa0.8Mg0.2O2.825 (D = Ba and Ca) electrolytes in solid oxide fuel cells

La0.85DxSr0.15–xGa0.8Mg0.2O2.825 (D = Ba and Ca, x = 0, 0.01, 0.03, 0.05, and 0.07) electrolytes were synthesized using a solid-state reaction method, calcined at 1400 °C for 5 h, and sintered at 1400 °C for 5 h. The microstructures, electrical properties, and cell performances of the electrolytes and fuel cells were analyzed by X-ray diffraction, scanning electron microscopy, impedance analysis, and electrochemical analysis. La0.85BaxSr0.15–xGa0.8Mg0.2O2.825 (LBSGM) and La0.85CaxSr0.15–xGa0.8Mg0.2O2.825 (LCSGM) exhibit a dense structure and a cubic perovskite phase. Further, they contain small amounts of a secondary phase. The lattice constants of LBSGM and LCSGM are 0.3913–0.3914 nm and 0.3906–0.3909 nm, respectively. The average grain size of the sample increases with increasing Ba2+ or Ca2+ content. The conductivity of LCSGM (0.197–0.174 S/cm) is usually higher than that of LBSGM (0.181–0.162 S/cm) at 800 °C. The cells with La0.85Sr0.15Ga0.8Mg0.2O2.825 and La0.85Ca0.03Sr0.12Ga0.8Mg0.2O2.825 electrolytes exhibit high open-circuit voltages and maximum power densities of 0.96 V and 542 mW/cm2 and 0.94 V and 567 mW/cm2, respectively, at 800 °C.

Influence of Al-doping on the structural, magnetic, and electrical properties of La0.8Ba0.2Mn1−xAlxO3 (0 ⩽ x ⩽ 0.25) manganites

We have studied the effect of Al doping on structural, magnetic and electrical properties of La0.8Ba0.2Mn1-xAlxO3(0⩽x⩽0.25) manganite annealed in 750° and 1350° temperatures. Results show Tc decreases as Al ion substitution in Mn site. The magnetic susceptibility measurement shows Griffiths and spin-glass phase in aluminum-doped samples. Recently, Narreto et al., reported dynamic distortion and polaronic effects in the paramagnetic state of La0.8Ba0.2Mn1-xAlxO3 manganites. Here we completed the phase diagram and show an occurrence of the spin-glass state in this manganite. The resistivity measurement shows, TMIT (metal-insulator) transition temperatures decreases and the system become an insulator. The insulator–metal transition occurs for the undoped sample annealed at the low temperature in near 165 K, while this transition is weak for the undoped sample annealed at high temperature due to oxygen non-stoichiometry. Using three models VIZ., Adiabatic small polaron hoping, Variable range hopping, and Percolation model, the resistivity have been studied.

Correlation between magnetocaloric and electrical properties based on phenomenological models in La0.47Pr0.2Pb0.33MnO3 perovskite

ABSTRACTWe have investigated the correlation between magnetocaloric and electrical properties of La0.47Pr0.2Pb0.33MnO3 perovskite prepared using the sol–gel method. Rietveld analysis of X-ray diffraction (XRD) pattern shows pure crystalline phase with rhombohedral structure. Magnetic entropy change, relative cooling power (RCP) and specific heat were predicted from M(T, μ0H) data at different magnetic fields with the help of the phenomenological model. The magnetic entropy change reaches a maximum value of about 3.96 J kg−1 K−1 for μ0H = 5 T corresponding to RCP of 183 J kg−1. These values are relatively higher, making our sample a promising candidate for the magnetic refrigeration. Electrical-resistivity measurements were well fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic-metallic clusters and paramagnetic-semiconductor regions. The temperature and magnetic field dependences of resistivity data, ρ(T, μ0H), allowed us to determine the magnetic entropy change . Results show that the as-obtained magnetic entropy change values are similar to those determined from the phenomenological model.

Effects of silver doping on structure and electrical properties of La0.67Ca0.23K0.1MnO3 polycrystalline ceramic

In this work, La0.67Ca0.23K0.1MnO3:Agx (x = 0.1, 0.2, 0.3, 0.4, 0.5) polycrystalline ceramic samples were prepared by sol-gel method, and their structural and electrical properties were systematically investigated. X-ray diffraction (XRD) analysis showed that crystal structures of all samples were rhombohedral. Surface morphology was investigated by scanning electron microscopy (SEM), which indicated that the number of pores increased with the increase in Ag content. Elemental mapping image showed that Ag was uniformly distributed over the entire sample on macro-scale, which could create conduction channels and improve the connectivity of grains. Therefore, the resistivity decreased sharply with the increase in Ag content. Standard four-probe method was used to measure temperature dependence of resistivity (ρ-T). Insulator-metal transition temperature (TP) shifted to higher temperature when the value of x was below 0.3. Temperature coefficient of resistivity (TCR%) decreased as Ag content increased. Fitted curves for resistivity of LCKMO:Agx composites at low temperature range (T <TP) indicated that grain boundary effects, electron-electron scattering and electron-magnon scattering mechanisms were involved. High-temperature (T >TP) resistivity data were explained using small-polaron hopping (SPH) and variable-range hopping (VRH) models. Resistivity data over the entire temperature range (100–300K) could be fitted by percolation model.

Electrical properties of La0.85Sr0.15Ga0.8Mg0.2O3−δ samples prepared by one- or three-stage solid-state calcination process

La0.85Sr0.15Ga0.8Mg0.2O3−δ (LSGM1520) samples are prepared by one- or three-stage solid-state calcination process. The influence of calcination and sintering parameters on the densification, grain size, phase structure, conductivity, and activation energy of LSGM1520 electrolyte samples are investigated and the most suitable process method is identified. The results show that the three-stage calcination procedure is effective in preparing higher purity LSGM1520 powders than those obtained with the traditional one-stage calcination procedure. Conductivities of the A2 and C4 electrolyte samples at 800 °C are 0.18 and 0.17 S cm−1, respectively. The A2 and C4 of LSGM1520 electrolyte samples are from the one-stage and three-stage calcination procedures, respectively. The open-circuit voltage and maximum power density values of cells prepared using A2 and C4 as electrolytes at 800 °C are 1.01 V and 370 mW cm−2, and 0.97 V and 367 mW cm−2, respectively. Hence, the A2 electrolyte sample, prepared though a simpler process than the C4 electrolyte, displays good cell performance. Although the A2 sample contains a very small amount of secondary phase, its conductivity and cell performance are not significantly reduced at temperatures above 700 °C, as expected.

Preparation, structure and electrical properties of La1−xBaxCrO3 NTC ceramics

The La1-xBaxCrO3 (x = 0-0.2) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid-state reaction method at 1600 A degrees C. Scanning electron microscope images show that the doping of Ba2+ contributes to the increase in the density. X-ray diffraction analysis has revealed that the sintered ceramics crystallize in a single perovskite structure. X-ray photoelectron spectroscopy analysis confirm the existence of Cr3+ and Cr6+ ions on lattice sites, which result in hopping conduction. The presence of the Cr3+ and Cr6+ ions is one of the significant factors that affect the electrical conductivity of La1-xBaxCrO3 ceramics. The resistance of NTC thermistors decreases with the increase of Ba content as a result of the enhancement of Cr6+ Concentration. The obtained values of rho (-50), B (-50/-25) and E (a) are in the range of 49.278-1.9839 x 10(5) Omega cm, 1767.4-3496.9 K, 0.1523-0.3013 eV, respectively.

Correlation between structural, magnetic and electric properties of La0.5Ca0.3Te0.2MnO3 sample synthesis by sol-gel method

The structural, magnetic and electric properties of the sample have been investigated. The crystal structure estimated via X-ray powder diffraction indicates that this system is characterized by a single phase and crystallizes in the orthorhombic structure with space group Pnma. The results of Hirshfeld surface indicate that the intermolecular electrostatic interactions are in short range verifying so that the magnetic interactions have been still in short range. The values of critical exponents obtained from the resistivity and from magnetic measurements are very close to those predicted based on the mean field tri-critical model.