Electrical Properties Of La0 Research Articles

Electrical Properties of La0.67Sr0.33Mn0.8Ni0.2O3 Synthesized by Sol Gel Method

The previous study of lanthanum manganites showed that physical properties of LaMnO3 compound has changed when Sr doped the La site. La0.67Sr0.33MnO3 compound give the highest TC = 370 K and showed metal insulator transition. It happens as a result of changed in Mn3+/Mn4+ ratio. Its indicated that Mn has the most important rule to the physical properties changed. In order to shift Tc of the compound to the near room temperature, Ni doped was given to Mn site of LSMO. In this paper, 20% Mn site was doped by Ni. La0.67Sr0.33Mn0.8Ni0.2O3 compound synthesized by sol gel method and characterized using XRD. Then, single phase compound resisitivity was measured to see the electrical properties this compound. The XRD result showed that sample have single phase with rhombohedral structure and R-3c space group. Resistivity as a temperature function graph does not show resistivity peak and metal insulator transition. The resistivity measurement showed that below 300 K, resistivity inscreased with decreased of temperature that indicates insulator behavior. It caused by decreased of double exchange interaction and increase of superexchange interaction. From this result, we can conclude that Ni doped decreased electrical properties of the sample.

Effects of A-Site Doping on Structural, Magnetic, and Electrical Properties of La0.8−x A x Sr0.2MnO3 (0 ≤ x ≤ 0.6) Manganites (A = Pr, Nd, and Gd)

The effects of rare-earth doping were investigated on the structural, magnetic, and electrical properties of La0.8−xAxSr0.2MnO3 (0 ≤ x ≤ 0.6) manganites. Results showed that the Pr- and Nd-doped samples were single phase and crystallized in the rhombohedral structure with an R-3C space group. The Gd-doped samples were also single phase for values of x equal to 0 and 0.1 but secondary phases were detected for higher doping levels (i.e., increasing mismatch of the ionic lattice). Moreover, the crystal structure was observed to transform from a rhombohedral (x = 0, 0.1) to an orthorhombic (x ≥ 0.2 samples) one with the Pnma space group. In all the samples, reducing ionic radius of the dopant ion led to a reduction in the unit cell volume. ac magnetic susceptibility measurements showed that in the Pr- and Nd-doped samples, the transition temperature decreased from a paramagnetic (PM) to a ferromagnetic (FM) one with decreasing ionic radius of dopant elements. A frequency-dependent peak was observed in the ac susceptibility for x = 0.4, 0.5, and 0.6, revealing the presence of a spin-glass state at low temperatures. The Curie temperature (TC) for the Gd-doped samples changed nonuniformly due to the formation of secondary phases. However, no spin-glass behavior was observed in the Gd-doped samples. The temperature dependence of resistivity indicated that the Nd- and Pr-doped samples with low doping levels contained an FM metal, while those with higher doping levels exhibited an FM-insulator behavior. In the Gd-doped series, the FM-metallic phase was observed in all the doped samples. In order to understand the transport mechanism, several theoretical models such as small polaron hopping and variable-range hopping were explored to fit the resistivity data; the results confirmed our experimental data.

Structural and electrical properties of La0.9Dy0.1MnO3 prepared by sol–gel technique

Nanosized particles of La0.9Dy0.1MnO3 were prepared by sol–gel technique using citric acid as a chelating agent. The compound was analysed by powder X-ray diffraction technique and found to be single-phased orthorhombic in structure with space group Pnma which was confirmed with standard JCPDS data. The structural and morphological characterisations of synthesised material were carried out using XRD, Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectrometer. The magnetic study at room temperature shows the paramagnetic behaviour of the material. The existence of space charge polarisation and relaxation is due to the presence of oxygen vacancy illustrated from the real and imaginary part of impedance, respectively. The activation energy of synthesised material is calculated using Arrhenius equation from the impedance spectroscopy which corresponds to the existence of oxygen vacancy.

Enhancement of the interfacial polarization resistance of La0.6Sr0.4Co0.2Fe0.8O3-δ cathode by microwave-assisted combustion method

Thermogravimetry, phase formation, microstructural evolution, specific surface area, and electrical properties of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode were studied as functions of its preparation technique. The pure perovskite LSCF cathode powder was synthesized through glycine–nitrate process (GNP) using microwave heating technique. Compared with conventional heating technique, microwave heating allows the rapid combustion to occur simultaneously between the nitrates and glycine in a controllable manner. The resulting powder is a single-phase nanocrystallite with a mean particle size of 113nm and a high specific surface area of 12.2m2/g, after calcination at 800°C. Impedance analysis indicates that microwave heating has significantly reduced the polarization resistance of LSCF cathode. The area specific resistance (ASR) value of 0.059 and 0.097Ωcm2 at 800°C and 750°C, respectively, were observed. These values were twofold lower than the corresponding ASR of the cathode (0.133 and 0.259Ωcm2 at 800°C and 750°C, respectively) prepared through conventional heating. Results suggest that the microwave heating GNP strongly contributes to the enhancement of the LSCF cathode performance for intermediate temperature solid oxide fuel cells.

Effect of Ca-doping on the electrical properties of La0.2Nd0.47Sr0.33MnO3 ceramics prepared by sol–gel technique

A series of ceramic samples La0.2Nd0.47Sr0.33−xCaxMnO3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were prepared by sol–gel technique. The crystal structure was analyzed by X-ray diffraction, which reveals that all the samples are single-phase without any detectable secondary phases. The grain size and surface morphology were investigated by scanning electron microscope ,which indicates that ceramic samples with better crystallization have high density. The resistivity dependence of the temperature (R-T) of the bulk samples was studied by the standard four-probe method. The result of the R-T curves shows that the metal-insulator transition temperature shifts to the lower temperature and the resistivity as well as the maximum value of the temperature coefficient of resistivity increase. It is usually interpreted as the Ca-doping decreases the A-site cationic radius and the tolerance factor, which results in MnO6 octahedral tilting and the decrease of the double exchange between Mn3+ and Mn4+.

Effects of Ag addition on the structural and electrical properties of La0.67Sr0.33MnO3 ceramics

ABSTRACTLa0.67Sr0.33MnO3:mol-%Agx (LSMO:Agx, x = 0, 0.1, 0.2, 0.3 and 0.4) polycrystalline ceramics were prepared by chemical co-precipitation methods. All of the LSMO:Agx samples showed rhombohedral perovskite structure with a space group of . The diffraction peaks of metallic Ag did not appear in the XRD graph, due to the Ag substitution at A sites (La3+ or Sr2+ ions) and the evaporation loss of the element Ag in the process of high-temperature sintering, or the residual amount of Ag beyond the sensitivity of the XRD. With the increase of Ag addition, unit cell volume (V), metal−insulator transition temperature (Tp) and conductivity at Tp (ρTp) of the LSMO:Agx samples increased significantly. At the same time, the temperature coefficient of resistance (TCR%), temperature peak of the TCR% (Tk) and the figure of merit (Z) reached the optimal values of 3.3% K−1, 367 K and 0.049 at x = 0.3. Ag substitution at A sites (La3+ or Sr2+ ions) and gathering at grain boundaries (GBs) were proposed to explain the existence of Ag addition. All results suggested that the enhancement of electrical properties was due to silver-doping and it increased the bond angles of Mn−O−Mn (θMn−O−Mn) and the bond distance of Mn−O (dMn−O), improving Mn4+ concentration, grain sizes and GBs connectivity in LSMO:Agx ceramics.

Investigation of the magnetocaloric effect and the electrical properties of La0.8Ba0.1Ca0.1Mn0.85Co0.15O3 oxide manganite

The La0.8Ba0.1Ca0.1Mn0.85Co0.15O3 sample was prepared by polymerization complex sol-gel method. The structural, magnetocaloric and electrical properties were studied. The sample crystallizes in the orthorhombic structure with Pbnm space group. In addition to the experimental study, theoretical approaches were adopted to investigate the magnetocaloric and electrical behavior of this sample. The important parameters such as maximum entropy change, full width at half maximum(δFWHM)and relative cooling power (RCP) were explained qualitatively. The analysis of electrical resistivity data shows the semiconductor behavior in all temperatures, which can be explained by small polaron hopping (SPH) and Mott's variable range hopping (VRH) models.

Magnetic and electrical response of Co-doped La0.7Ca0.3MnO3 manganites/insulator system

We present a systematic study of the structural, magnetic and electrical properties of La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.3Mn0.95Co0.05O3 (LCMCO0 perovskite manganites. Most of the work is devoted to the electrical properties with a thorough discussion about different models for both the metallic and insulator states. With a view to understand the conduction mechanism in these materials, the resistivity of both materials was measured over a temperature range 5–300K and in a magnetic field up to 1T and the data were analysed by using several theoretical models. It has been observed that the metallic part of the temperature dependent resistivity (ρ) curve fits well with ρ=ρ0 +ρ2⊡5Τ2⊡5, indicating the electron–magnon scattering processes in the conduction of these materials. On the other hand, in the high temperature paramagnetic insulating regime, the adiabatic small polaron and VRH models fit well, thereby indicating that polaron hopping might be responsible for the conduction mechanism.

Effect of 20% Cr-doping on structural and electrical properties of La0.67Ca0.33MnO3 perovskite

Structural and electrical properties of La0.67Ca0.33Mn1-xCrxO3 (x = 0 and 0.2) manganites are studied in this work. The samples were prepared using Pechini sol-gel method at 1173 K. Rietveld analysis of X-ray diffraction (XRD) patterns shows the formation of pure crystalline phase with orthorhombic Pnma structure with a decrease of the unit cell volume and crystalline domain size when increasing Cr-content. Electrical properties of the samples have been investigated using complex impedance analysis in 180–320 K temperature range with varying frequency between 40 and 106 Hz. For both samples, frequency dependence of imaginary part of impedance (Z″) shows the existence of relaxation phenomenon. The impedance study using Nyquist representation revealed the appearance of semicircle arcs and an equivalent circuit of the type of R1 + (R2//ZCPE) has been proposed to explain the impedance results. The conductance curves were analyzed by Jonscher power law and the deduced activation energy values are close to those calculated from relaxation time indicating that relaxation process and conductivity have the same origin.

Influence of Cr deficiency on sintering, thermal expansion and electrical properties of La0.75Sr0.25Cr1−xO3−δ as a SOFC interconnect material

The SOFC interconnect materials La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] [Formula: see text]–[Formula: see text] were prepared using an auto-ignition process. The influences of Cr deficiency on their sintering, thermal expansion and electrical properties were investigated. All the samples were pure perovskite phase after sintering at 1400[Formula: see text]C for 4 h. The cell volume of La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] decreased with increasing Cr deficient content. The relative density of the sintered bulk samples increased from 93.2% [Formula: see text] to a maximum value of 94.7% [Formula: see text] and then decreased to 87.7% [Formula: see text]. The thermal expansion coefficients of the sintered bulk samples were in the range of [Formula: see text]–[Formula: see text] (30–1000[Formula: see text]C), which are compatible with that of YSZ. Among the investigated samples, the sample with 0.02 Cr deficiency had a maximum conductivity of 40.4 Scm[Formula: see text] and the lowest Seebeck coefficient of 154.8 [Formula: see text]VK[Formula: see text] at 850[Formula: see text]C in pure He. The experimental results indicate that La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] has the best properties and is much suitable for SOFC interconnect material application.

Correlation between magnetic and electric properties of La0.5Ca0.3Ag0.2MnO3 based on critical behavior of resistivity

The relationship between electrical and magnetic properties of manganites has been traced through the analysis of temperature dependence of the La0.5Ca0.3Ag0.2MnO3 resistivity. The measurement of resistivity versus temperature ρ(T) of the sample shows a paramagnetic semiconductor-ferromagnetic metallic transition at T=TMS. The application of magnetic field increases the TMS value and reduces the resistivity of the compound. The estimated critical exponents are (β=0.273±0.01; γ= 1.074±0.02 and α=0.456). The values of these exponents obtained from resistivity are very close to them predicted by the tri-critical mean-field model. These results are in good agreement with the analysis of critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic semiconductor regions. So, we found that the estimated results are in adequate accordance with experimental data.

Strain Dependence of Magnetic and Transport Properties in Half-Doped La0.5Ca0.5MnO3Films

Tensile strain effects on the magnetic and electrical properties of La0.5Ca0.5MnO3 (LCMO5) films deposited on SrTiO3 (001) substrates are investigated with varying the thickness of LCMO5 from 16.5 to 62.2 nm. A microstructure analysis indicates that the film remains tensile-strain state with its thickness thinner than 50 nm. Magnetic measurements show that the ferromagnetic (FM) transition temperature ( ${T_{C}}$ ) of the films increases from 250 to 265 K with the film evolving from tensile to relaxed state. Meanwhile, the saturation magnetization at 5 K increases from 21.88 to 43.88 emu/cm3. It is interesting to find that colossal magnetoresistance is drastically enhanced from 18% to 740% with increasing the film thickness from 22.2 to 62.2 nm, which is attributed to the relaxation of tensile strain in association with an enhancement of FM interaction within an antiferromagnetic matrix.

Effect of Screen-Printing Mesh Opening Diameter on Microstructural and Electrical Properties of La0.6Sr0.4Co0.2Fe0.8O3−δ Thick Films

The performance of solid oxide fuel cells (SOFCs) is hampered by the large polarization and ohmic losses across the cathode–electrolyte interface. To minimize these losses, in most SOFCs the cathode is obtained by thick-film deposition techniques. Since the properties of such films depend upon the starting materials and screen-printing parameters, the effect of the mesh opening diameter on the physiochemical properties of cathodes for intermediate-temperature (IT)-SOFCs has been studied. Combustion-synthesized La0.6Sr0.4Co0.2Fe0.8O3−δ powder with specific surface area of 11.64 m2 g−1 was utilized in film formation. All films were porous in nature, and the thickness was observed to increase with the mesh opening diameter. The electrical conductivity showed a decreasing trend with film thickness. Typically, film with 7 μm thickness showed moderate conductivity of 16.4 S cm−1 with Ea = 0.1 eV.

ChemInform Abstract: Structural, Magnetocaloric, Electrical Properties and Theoretical Investigations in Manganite La0.67Sr0.1Ca0.23MnO3 Type Perovskite

AbstractReview: 42 refs.

Enhanced electrical and magnetic properties in La0.7Sr0.3MnO3thin films deposited on CaTiO3-buffered silicon substrates

We investigate the suitability of an epitaxial CaTiO3 buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of the colossal magnetoresistive material La0.7Sr0.3MnO3 with silicon. The magnetic and electrical properties of La0.7Sr0.3MnO3 films deposited by MBE on CaTiO3-buffered silicon (CaTiO3/Si) are compared with those deposited on SrTiO3-buffered silicon (SrTiO3/Si). In addition to possessing a higher Curie temperature and a higher metal-to-insulator transition temperature, the electrical resistivity and 1/f noise level at 300 K are reduced by a factor of two in the heterostructure with the CaTiO3 buffer layer. These results are relevant to device applications of La0.7Sr0.3MnO3 thin films on silicon substrates.

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.

Effect of Ag addition on the magnetic and electrical properties of La0.67Ca0.33MnO3 films

La0.67Ca0.33MnO3:mol%Agx (LCMO:Agx, x=0, 0.04, 0.08, 0.10 and 0.20) films were prepared on the single crystalline (100)-orientated (LaAlO3)0.3–(SrAlTaO6)0.7 (LSAT) substrates by the pulsed laser deposition (PLD) method. With the increasing of Ag addition, the magnetoresistance (MR) of the LCMO:Agx films exhibits a significant decrease and the x=0 sample reach to the maximum value of MR ratio at 46.6% under 1T magnetic field, in addition, the metal–insulator transition temperature (Tp) improve 20–26K or 12–18K for the films at a zero or 1T fields, respectively. The results maybe due to the fact that Ag enter the host lattice, partially substitute for La3+/Ca2+ ion, and then increase the Mn4+/Mn3+ ratio, which lead to enhance the electrical properties in LCMO:Agx films.

Effect of A-site cation size on the structural, magnetic, and electrical properties of La1−xNdxMn0.5Cr0.5O3 perovskites

A systematic investigation of rare earth chromium manganites with general formula La1−xNdxMn0.5Cr0.5O3 (x=0.0, 0.3, 0.6 and 0.9) has been undertaken mainly to understand their structural, magnetic as well as electrical behavior. Upon Nd doping on La site, unit cell volume and the B–O–B bond angle are reduced. The magnetic interactions in the materials are predominantly ferromagnetic and we believe that double exchange interactions between Mn3+ and Mn4+, and Mn3+ and Cr3+ should be the origin of ferromagnetism. The Curie temperature decreases with increasing Nd content. All the samples are semiconducting throughout the temperature range studied. The electric transport behavior can be described by the adiabatic small polaron hoping model, with an apparent increase of polaron activation energy with Nd content.

Preparation and Electrical Properties of La0.9Sr0.1TiO3+δ.

La1−xSrxTiO3+δ (LST) has been studied in many fields, especially in the field of microelectronics due to its excellent electrical performance. Our previous theoretical simulated work has suggested that LST has good dielectric properties, but there are rare reports about this, especially experimental reports. In this paper, LST was prepared using a solid-state reaction method. The X-rays diffraction (XRD), scanning electron microscope (SEM), broadband dielectric spectroscopy, impedance spectroscopy and photoconductive measurement were used to characterize the sample. The results show that the values of dielectric parameters (the relative dielectric constant εr and dielectric loss tanδ), dependent on temperature, are stable under 350 °C and the value of the relative dielectric constant and dielectric loss are about 52–88 and 6.5 × 10−3, respectively. Its value of conductivity increases with rise in temperature, which suggests its negative temperature coefficient of the resistance. In addition, the band gap of LST is about 3.39 eV, so it belongs to a kind of wide-band-gap semiconductor materials. All these indicate that LST has anti-interference ability and good dielectric properties. It could have potential applications as an electronic material.

Influence of Grinding Particle Size on Structure and Electrical Properties of La0.67Sr0.33MnO3−δ Compound

In this article, the influences of grinding particle size on the structure and electrical transport properties of La0.67Sr0.33MnO3−δ compound have been investigated. The compound was prepared by gel combustion process followed by grinding for different duration time. It was found that the lattice parameters, unit-cell volume, strain, oxygen deficiency, and temperature dependence of resistivity ρ–T increase with decreasing particle size. The ρ–T growth can be explained by the increasing contribution of the grain boundary effect, strain, and even oxygen deficiency. The electrical transport mechanism over the whole temperature range of 100–400 K was thoroughly described by applying the phase separation model around the phase transition temperature TP. This model was subsequently employed to calculate the ρ–T at high temperature up to 1000 K. The result showed there was a second phase transition at a typical temperature T*>TP, which could be attributed to the relaxation of small polarons to large ones. This relaxation occurred at lower temperatures when the particle size decreased. It might be due to the decrease in conduction bandwidth caused by the defects arisen during the grinding.