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1.
The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4. The dynamic magnetic properties investigated using frequency-dependent ac magnetic susceptibility fitted using different phenomenological models such as Neel–Arrhenius, Vogel–Fulcher and power law, strongly indicate the presence of a cluster-glass-like behavior of Cu1.5Mn1.5O4 at 40 K. The magnetization data have revealed that our compound displays an occurrence of second-order paramagnetic (PM) to ferrimagnetic (FIM) phase transition at the Curie temperature TC = 80 K as the temperature decrease. In addition, the magnetic entropy change (ΔSM) was calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement was found between both sets of data, which proves the importance of both electron interaction and magnetoelastic coupling in the magnetocaloric effect (MCE) properties of Cu1.5Mn1.5O4. The relative cooling power (RCP) reaches 180.13 (J kg−1) for an applied field at 5 T, making our compound an effective candidate for magnetic refrigeration applications. The critical exponents β, γ and δ as well as transition temperature TC were extracted from various techniques indicating that the magnetic interaction in our sample follows the 3D-Ising model. The validity of the critical exponents is confirmed by applying the Windom scaling hypothesis.

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4.  相似文献   

2.
In the present study, the structural, morphological, electrical, and dielectric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 annealed at 600 °C, 900 °C, and 1200 °C were investigated. The X-ray diffraction patterns confirmed the presence of the single-phase cubic spinel structure with the Fd3̄m space group. The SEM images of Ni0.6Zn0.4Fe1.5Al0.5O4 nanoparticles demonstrated that these samples (Ni900 and Ni1200) were nano-sized and that the increase in annealing temperature enhanced the agglomeration rate. It was found that the electrical conductivity of the system improved on increasing the temperature over the whole explored range for the two low annealing temperatures, while this improvement declined after 500 K in the case of the highest annealing temperature. For such a sample, a metallic behavior was seen. The sample annealed at 1200 °C possessed the highest conductivity and the lowest activation energy. The impedance measurements were in good agreement with the conductivity plots and confirmed the emergence of a grain boundary effect with the increase in annealing temperature. For the sample annealed at the highest temperature, Z′ decreased rapidly with frequency. This sample exhibited the lowest defect density than the other samples. Consequently, its electrical conductivity increased. A Nyquist diagram was used to examine the contribution of the grains and grain boundary to conduction and to model each sample by an equivalent electrical circuit. The dielectric behavior of the investigated samples was correlated to the polarization effect.

In the present study, the structural, morphological, electrical, and dielectric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 annealed at 600 °C, 900 °C, and 1200 °C were investigated.  相似文献   

3.
The compound NaCu0.2Fe0.3Mn0.5O2 was synthesized using a solid-state method and it crystallized in a hexagonal system with a R3̄m space group in an O3-type phase. The optical properties were measured using UV-Vis absorption spectrometry to determine the absorption coefficient α and the optical band gap Eg. The optical band gap energy of this sample is 2.45 eV, which indicates that it has semiconductor characteristics. Furthermore, the electrical and dielectric properties of the material were investigated using complex impedance spectroscopy between 10−1 Hz and 106 Hz at various temperatures (333–453 K). The permittivity results prove that there are two types of polarization, dipolar polarization and space charge polarization. The Nyquist diagrams show the contribution of the effects of the grain, grain boundary, and electrode properties. The frequency dependence of the conductivity was interpreted in terms of Jonscher''s law. The DC conductivity follows both the Mott and Arrhenius laws at low and high temperature, respectively. The temperature dependence of the power law exponent(s) suggests that the overlapping large polaron tunneling (OLPT) model is the dominant transport process in this material. The optimum hopping length of the polaron (4 Å) is large compared with the interatomic spacing (2.384 Å for Na–O and 2.011 Å for Cu, Fe, Mn–O).

The compound NaCu0.2Fe0.3Mn0.5O2 was synthesized using a solid-state method and it crystallized in a hexagonal system with a R3̄m space group in an O3-type phase.  相似文献   

4.
The particle surface of LiNi0.5Mn1.5O4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiOx’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi(0.5−w)Mn(1.5+w)−tTitO4 phase and Ti-rich LiNi0.5Mn1.5−yTiyO4 segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li+. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.

LiNi0.5Mn1.5O4−δ surface is doped with Ti ion maintaining the spinel structure at 500 °C, higher annealing temperatures cause Ti diffusion from surface towards the core.  相似文献   

5.
The room temperature structural, optical and dielectric properties of Mg0.95Mn0.05O and Mg0.95Mn0.01TM0.04O (TM = Co, Ni, and Cu) nanoparticles are reported. All transition metal nanocrystalline samples were successfully prepared by sol–gel auto combustion method. X-ray powder diffraction patterns at room temperature confirmed the formation of single-phase cubic structure with an Fm3̄m space group for all prepared samples. Slight variation in the lattice parameter of TM doped Mg0.95Mn0.05O has been observed. Using Rietveld refinement of XRD data, the space group and lattice parameters are determined. Scanning electron microscopy (SEM) measurements were performed to understand the morphology and grain size of the Mg0.95Mn0.01TM0.04O (TM = Co, Ni, and Cu) nanocrystals. The estimated band gaps as calculated by using UV-Vis spectroscopy are found to be 3.59, 3.61, 5.63 and 3.55 eV for Mg0.95Mn0.05O and Mg0.95Mn0.01TM0.04O (TM = Co, Ni, and Cu) nanocrystals, respectively. Both dielectric constant and dielectric loss is found to decrease due to TM (transition metal) doping. The ac conductivity is found to increase with increase in frequency. Electric modulus spectra reflect the contributions from grain effects: the large resolved semicircle arc caused by the grain effect. The results obtained in this study were discussed comparatively with those cited in the literature.

The room temperature structural, optical and dielectric properties of Mg0.95Mn0.05O and Mg0.95Mn0.01TM0.04O (TM = Co, Ni, and Cu) nanoparticles are reported.  相似文献   

6.
Spinel LiNi0.5Mn1.5O4 shows promise as a potential candidate for Li-ion batteries due to its high energy density and high rate performance. However, LiNi0.5Mn1.5O4 (LNMO) spinel oxides usually deliver poor cycle life because of the increasing impedance and gradually dissolving Mn resulting in the destruction of crystal structure. Here, a conductive polymer poly-(3,4-ethylenedioxythiophene) (PEDOT) surface modified strategy is introduced to settle the above challenges. The main purpose is to construct a uniform and dense shell film on the surface of LiNi0.5Mn1.5O4 (Industrial Grade), which is prepared by a simple chemical in situ oxidative polymerization method. The Mn dissolving from the lattice during the long-term cycling is well inhibited as the polymer shell protects LiNi0.5Mn1.5O4 from direct exposure to the highly active electrolyte. As expected, the 3 wt% poly-(3,4-ethylenedioxythiophene) coated sample reveals long cycle life with acceptable capacity of 114.5 mA h g−1 and high capacity retention of 91.6% after 200 cycles, compared to 70.9 mA h g−1 and 56.5%, respectively, for the bare LiNi0.5Mn1.5O4 sample. Furthermore, the coated sample demonstrates a higher capacity of 110 mA h g−1 and 63 mA h g−1 at 5C and 10C rate respectively. The improved performance is believed to be attributed to the formation of high conductivity and stable interface structure between electrolyte and LNMO, which is beneficial to suppress the destruction of crystalline structure due to the Mn dissolution and undesired side-reaction between electrolyte and LiNi0.5Mn1.5O4 in long cycle, and improve simultaneously the conductivity and interface stability of LiNi0.5Mn1.5O4 for high voltage lithium-ion batteries.

PEDOT coating on LNMO surface effectively improves it''s the crystal structure stability and electrochemical properties.  相似文献   

7.
An Ru-doped spinel-structured LiNi0.5Mn1.5O4 (LNMO) cathode has been prepared via a simple hydrothermal synthesis method. The as-prepared cathode is characterized via Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size distribution analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry performance tests. The FTIR spectroscopy and XRD analyses show that the Ru-doped LNMO has a good crystallinity with a disordered Fd3̄m space group structure. The disordered structure in the cathode increased and the LixNi1−xO impurity phase decreased when Ru addition increased. SEM shows that all samples are octahedral particles with homogeneous sizes distribution, and the particle size analysis shows that the Ru-doped samples have smaller particle size. XPS confirms the existence of Ru ions in the sample, and reveals that the Ru induce to part of Mn4+ transfers to Mn3+ in the LNMO. The electrochemical property indicated that the Ru-doped cathode exhibits better electrochemical properties in terms of discharge capacity, cycle stability and rate performance. At a current density of 50 mA g−1, the discharge specific capacity of the Ru-4 sample is 140 mA h g−1, which is much higher than that of the other samples. It can be seen from the rate capacity curves that the Ru-doped samples exhibit high discharge specific capacity, particularly at high current density.

An Ru-doped spinel-structured LiNi0.5Mn1.5O4 (LNMO) cathode has been prepared via a simple hydrothermal synthesis method.  相似文献   

8.
The orthorhombic Pr0.8Na0.2MnO3 ceramic was prepared in polycrystalline form by a Pechini sol–gel method and its structural, magnetic, electrical and dielectric properties were investigated experimentally. A structural study confirms that the sample is single phase. Magnetic measurements show that the sample is a charge ordered manganite. The sample undergoes two successive magnetic phase transitions with the variation of temperature: a charge ordering transition occurred at TCO = 212 K followed by a paramagnetic (PM) to ferromagnetic (FM) transition around TC = 115 K. From an electrical point of view, a saturation region was marked in the conductivity as a function of temperature σ(T) curves at a specific temperature. The dc-conductivity (σdc) reaches a maximum value at 240 K. The obtained results are in good agreement with the temperature dependence of the average normalized change (ANC). We found that the conduction mechanism was governed by small polaron hopping (SPH) in the high temperature region and by variable range hopping (VRH) in the low temperature region. Complex impedance analysis indicates the presence of a non-Debye relaxation phenomenon in the system. Also, the compound was modeled by an electrical equivalent circuit. Then, the contribution of the grain boundary in the transport properties was confirmed.

The orthorhombic Pr0.8Na0.2MnO3 ceramic was prepared in polycrystalline form by a Pechini sol–gel method and its structural, magnetic, electrical and dielectric properties were investigated experimentally.  相似文献   

9.
Nanoparticles of Li0.5ZnFe1.5O4 (LiZn2Fe3O8) with the spinel structure were prepared by a sol–gel auto-combustion method at two different annealing temperatures. X-ray diffractograms and Rietveld refinement confirmed the formation of the spinel structure. The morphology was analyzed by electron microscopy, which showed that the grains were composed of different crystallites. Elastic properties were determined from infrared spectroscopy. It was found that the elastic parameters increased with the increase in annealing temperatures. The band gap depends on the annealing temperature and it decreased on increasing the particle size. The conductivity of the specimen annealed at 500 °C followed either the Jonscher''s model or Drude''s model depending on the temperature range. This conductivity decreased when the annealing temperature was raised by 600 °C. AC conductivity was found to be controlled by the hopping model. A single relaxation phenomenon was evidenced for each sample from impedance analysis. The Nyquist diagram proved that the samples were simultaneously capacitive and resistive and also supported the presence of multiple relaxation times.

Nanoparticles of Li0.5ZnFe1.5O4 (LiZn2Fe3O8) with the spinel structure were prepared by a sol–gel auto-combustion method at two different annealing temperatures.  相似文献   

10.
Al-doped spinel LiNi0.5Mn1.5O4 materials with different sites and contents were synthesized by rapid precipitation combined with hydrothermal treatment and calcination. The roles of Al on structural stability and electrochemical performance were studied by utilizing a series of techniques. XRD patterns indicated lower ion diffusion and no impure phased in doped samples. FT-IR and CV results reveal that Al-doped materials possess a Fd3̄m space group with increased disorder and increasing amounts of Mn3+. SEM and TEM equipped with EDS were used to characterize the regular morphology accompanied by a complete crystal structure and homogeneous distribution of elements. The Al content at the Ni, Mn, and Ni/Mn sites was optimized to be 5%, 3% and 5% (in total), respectively. The cycling stability was considerably enhanced at an ambient temperature (25 °C) and high temperature (55 °C). A typical Al dual-doped sample at Ni/Mn sites with 5% content delivered a reversible capacity of 113.5 mA h g−1 after 200 cycles at 0.5C. The discharge capacity at 5, 10 and 20C was 127.3, 125.5 and 123.1 mA h g−1, respectively. The discharge capacity remained at 126 mA h g−1 after 50 cycles (55 °C, 0.5C). Subsequent EIS and analytical results of the cycled electrode showed improved structural stability with a lower resistance, stable cathode/electrolyte interface, and reduced dissolution of Mn. These data further demonstrated the feasibility and reliability of preparing high-performance spinel LiNi0.5Mn1.5O4 cathode materials by doping with a suitable amount of Al.

Al-doped spinel LiNi0.5Mn1.5O4 materials with different sites and contents were synthesized by rapid precipitation combined with hydrothermal treatment and calcination.  相似文献   

11.
Bulk-phase polycrystalline La1−xBixFeO3 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were prepared by citric sol–gel and sintering methods. The structural, morphological, and electrical properties of the resulting sol–gel solutions were investigated using various techniques. In an X-ray diffraction analysis, all samples crystallized in the orthorhombic structure with the Pbnm space group and showed an increase in lattice constant with increasing Bi content which was also confirmed by vibrational analysis. The sample surfaces and average grain sizes were examined by scanning electron microscopy. The grain distribution was non-uniform and the grain size increased with the increasing Bi content. The complex electrical conductivities and dielectric analyses of these materials were investigated as functions of frequency by impedance spectroscopy at various temperatures (75–200 °C). The frequency-dependent dielectric constant at each temperature increased with increasing Bi content. A Jonscher''s power law analysis revealed that the AC and DC conductivities arose by completely different mechanisms. The temperature dependence and dielectric relaxation of the DC conductivity satisfied the Arrhenius law and decreased with increasing Bi content. The activation energy ranged from 0.20 to 0.45 eV and was similar in the conduction and relaxation mechanisms, indicating that both transport mechanisms were based on hopping phenomena. We believe that lowering the activation energy will help with the optimization of constituents as promising candidates in novel materials for future electrocatalysts.

Bulk-phase polycrystalline La1−xBixFeO3 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were prepared by citric sol–gel and sintering methods.  相似文献   

12.
An La0.6Gd0.1Sr0.3Mn0.75Si0.25O3 ceramic was prepared via a solution-based chemical technique. X-ray diffraction study confirms the formation of the compound in the orthorhombic structure with the Pnma group space. Dielectric properties have been investigated in the temperature range of 85–290 K with the frequency range 40 Hz to 2 MHz. The conductivity spectra have been investigated by the Jonscher universal power law: σ(ω)  =  σdc  +  n, where ω is the frequency of the ac field, and n is the exponent. The deduced exponent ‘n’ values prove that a hopping model is the dominating mechanism in the material. Based on dc-electrical resistivity study, the conduction process is found to be dominated by a thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of a relaxation phenomenon and allows us to modelize the sample in terms of an electrical equivalent circuit. Moreover, the impedance study confirms the contribution of grain boundaries to the electrical properties.

A complex impedance spectrum for La0.6Gd0.1Sr0.3Mn0.75Si0.25O3 sample at different temperatures with electrical equivalent circuit.  相似文献   

13.
Herein, we investigated the correlation between the chemical composition, microstructure, and microwave properties of composites based on lightly Tb/Tm-doped Sr-hexaferrites (SrTb0.01Tm0.01Fe11.98O19) and spinel ferrites (AFe2O4, A = Co, Ni, Zn, Cu, or Mn), which were fabricated by a one-pot citrate sol–gel method. Powder XRD patterns of products confirmed the presence of pure hexaferrite and spinel phases. Microstructural analysis was performed based on SEM images. The average grain size for each phase in the prepared composites was calculated. Comprehensive investigations of dielectric properties (real (ε′) and imaginary parts (ε′′) of permittivity, dielectric loss tangent (tan(δ)), and AC conductivity) were performed in the 1–3 × 106 Hz frequency range at 20–120 °C. Frequency dependency of microwave properties were investigated using the coaxial method in frequency range of 2–18 GHz. The non-linear behavior of the main microwave properties with a change in composition may be due to the influence of the soft magnetic phase. It was found that Mn- and Ni-spinel ferrites achieved the strongest electromagnetic absorption. This may be due to differences in the structures of the electron shell and the radii of the A-site ions in the spinel phase. It was discovered that the ionic polarization transformed into the dipole polarization.

Paper presents the correlation between the composition, microstructure, and microwave properties of composites based on Tb/Tm-doped Sr-hexaferrites and spinel ferrites (AFe2O4), which were fabricated by a one-pot citrate sol–gel method.  相似文献   

14.
Bulk nanocrystalline samples of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (R3̄c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO6 octahedron and the reduction in the Curie temperature, Tc. A paramagnetic to ferromagnetic phase transition at TC is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn3+–O2−–Mn4+ bridges and weakens the double exchange (DE) interaction between Mn3+ and Mn4+ ions, which shows an obvious suppression of the FM interaction in the La0.65Ce0.05Sr0.3Mn1−xCuxO3 matrix. The maximum magnetic entropy change −ΔSmaxM is found to decrease with increasing Cu content from 4.43 J kg−1 K−1 for x = 0 to 3.03 J kg−1 K−1 for x = 0.15 upon a 5 T applied field change.

Bulk nanocrystalline samples of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.  相似文献   

15.
A series of Zn/Mn binary oxides with different molar ratios (1.4–11) were synthesized via co-precipitation from a solution obtained through the acidic (HCl) leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries. The oxides obtained were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Magnetic properties of the samples were also investigated. The Raman spectroscopy results showed all the binary metallic oxides belong to the ZnxMn3−xO4 (0.25 ≤ x ≥ 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn/Mn molar ratio; a maximum of 13.19 emu g−1 was found for the molar ratio of 11 at the Curie temperature (25.5 K). XPS showed that all the synthesized compounds contained Mn2+, Mn3+ and Mn4+. Mn2+ was the most prominent at a molar ratio of 11, Mn3+ was most common at a molar ratio of 2, and Mn4+ at 1.4.

A series of Zn/Mn binary oxides with different molar ratios were synthesized via co-precipitation from a solution obtained through the leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries.  相似文献   

16.
This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd3+ substitution at the B-site replacing Fe3+ ions. The synthesized composition of Ni0.7Zn0.2Co0.1Fe2−xGdxO4 (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd3̄m space group. The average particle size decreases due to Gd3+ substitution at Fe3+. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (TC) decreases from 731 to 711 K for Gd3+ substitution in Ni–Zn–Co ferrite. In addition, Gd3+ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρDC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd3+ in the Ni–Zn–Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η0) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni–Zn–Co ferrite tailored by Gd3+ substitution at the B-site replacing Fe3+ ions.  相似文献   

17.
(La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol–gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher''s power law σ(ω) = σdc + s, where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z′′) was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z′′ vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z′′ vs. Z′) at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.

(La0.8Ca0.2)1−xBixFeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol–gel method and calcined at 800 °C.  相似文献   

18.
In the present research, polycrystalline samples of La0.5Sm0.2Sr0.3Mn1−xCrxO3 are prepared using the self-combustion method. Then, we have studied their crystalline structure, and dielectric and electrical properties. The X-ray diffraction study shows that all the samples exhibit a single phase with orthorhombic structure (space group Pnma). The studied samples were also characterized by complex impedance spectroscopy in a wide range of temperatures and frequency. AC conductivity analyses are used to study the transport property of the investigated samples. These analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. It is also found that the conductivity decreases with Cr concentration. Complex impedance analysis confirms the contributions of grain and grain boundaries in the conduction mechanism. Finally, the impedance spectra, characterized by the appearance of semicircle arcs at different temperatures, were well modeled in terms of equivalent electrical circuits to explain the impedance results.

In the present research, polycrystalline samples of La0.5Sm0.2Sr0.3Mn1−xCrxO3 are prepared using the self-combustion method.  相似文献   

19.
Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form. The PdSn electrocatalyst was then impregnated with nickeltitanate by a microwave-assisted polyol method. The physiochemical characterisation of the synthesized electrocatalyst PdSn–Ni1−xMnxTiO3 was done by X-ray diffractometry, UV-visible spectrophotometry, Raman spectroscopy and transmission electron microscopy. The elemental composition was obtained using energy dispersive spectra which confirmed the presence of Ni, Mn, Ti, O, Pd and Sn. Electrochemical characterization using cyclic voltammetry and polarization experiments showed that the synthesized PdSn–Ni1−xMnxTiO3 exhibited an enhanced catalytic activity and better stability in the alkaline medium, compared to conventional PdSn/C catalysts. It was observed that the charge transfers from the support material (Ni1−xMnxTiO3) to the PdSn electrocatalyst boosted the oxidation reaction. By varying the methanol concentration from 0.5 M to 2.0 M, the resulting current density also varied from 129 to 151 mA cm−2. This result demonstrated that the prepared material PdSn–Ni1−xMnxTiO3/C electrocatalyst is an excellent candidate for the methanol oxidation reaction.

Nickeltitanate (Ilmenite) has been prepared with stoichiometric variation by substituting Mn in the ‘A’ site, using the sol–gel method in a highly active form.  相似文献   

20.
The dielectric properties of Ca0.85Er0.1Ti1−xCo4x/3O3 (CETCox) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCox decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop''s theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

Frequency dependence of real (ε′) part of permittivity of CETCox for x = 0.00, 0.05 and 0.10 for T = 600 K.  相似文献   

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