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1.
A systematic study focusing on the effect of Niobium (Nb) doping on the structural, magnetic and magnetocaloric properties of Ba2FeMoO6 samples is presented here. The samples of interest Ba2FeMo1?xNbxO6 (0 ≤ x ≤ 0.4) were prepared using the solid state reaction method and were confirmed to possess a cubic structure with Fm-3m space group using the X-ray diffraction analysis and Rietveld refinement. A second order of ferromagnetic phase transition was recorded in both the pure as well as the Nb doped samples using the temperature dependent magnetization and Arrott plots analysis. The pristine Ba2FeMoO6 (BFMO) sample indicated a spontaneous magnetization (34.6 emu/g at 100 K) with a relatively sharp magnetic transition at the Curie temperature (TC) of 315 K as compared to the doped samples. A magnetic entropy change of 0.93 Jkg?1K?1 at an applied magnetic field of 2.5 T was measured for the pure BFMO sample. The doped BFMO samples with Mo partially substituted by Nb however, were observed to effectively modify the TC accompanied by a decrease in magnetization. The results investigated in this work suggest that the magnetic and magnetocaloric properties of the BFMO can be tailored by controlled Nb doping which is of significant importance in order to realize the numerous potential applications of the material in the magnetic refrigeration technology.  相似文献   

2.
Bi1−xBaxFeO3 (x=0.05, 0.10 and 0.15) nanoparticles were synthesized by the sol–gel method. X-ray diffraction and Raman spectroscopy results showed the presence of distorted rhombohedral structure of Bi1−xBaxFeO3 nanoparticles. Rietveld refinement and Williamson–Hall plot of the x-ray diffraction patterns showed the increase in lattice parameters, unit cell volume and the particle size. Infrared spectroscopy and Raman analysis revealed the shifting of phonon modes towards the higher wavenumber side with increasing Ba concentration. These samples exhibited the optical band gap in the visible region (2.47–2.02 eV) indicating their ability to absorb visible light. Magnetic measurement showed room temperature ferromagnetic behavior, which may be attributed to the antiferromagnetic core and the ferromagnetic surface of the nanoparticles, together with the structural distortion caused by Ba substitution. The magnetoelectric coupling was evidenced by the observation of the dielectric anomaly in the dielectric constant and the dielectric loss near antiferromagnetic Neel temperature in all the samples.  相似文献   

3.
Multiferroics having composition Bi0.80Nd0.20-xBaxFeO3 were prepared to investigate the effect of doping on crystal structure, magnetic, and dielectric properties. The Rietveld refinement deduces the formation of mixed structural symmetry. With larger content of Nd, crystal structure consisting of major rhombohedral R3c and minor orthorhombic Pnma has been accomplished. The fraction of rhombohedral phase has been found to increase with doping of Ba up to x = 0.10. At composition x = 0.15, the orthorhombic phase Pnma disappears, and there is evolution of triclinic phase P1 in place of it. The mixed structure now accomplished contains ≈61% rhombohedral R3c and rest 39% triclinic P1. In solely Ba-doped sample (ie, at x = 0.20), the fraction of rhombohedral R3c phase again rises and attains ≈92% fraction of the structure along with rest triclinic P1 phase. The M-H loops depict enormous enhancement in magnetic properties with increasing doping of Ba. Dielectric constant (ε′) and dielectric loss (tan δ) both were found to increase with doping of Ba. The anomalies present in the dielectric constant and dielectric loss with temperature may be regarded to the hopping conduction of e between Fe3+ and Fe2+ and their interaction with oxygen vacancies.  相似文献   

4.
We report a study on the effect of the substitution of Bi3+ by Sr2+ on the stabilization of R3c structure of Bi1?xSrxFeO3 (0 ≤ x ≤ 0.3, Δx = 0.05), and its effect in the magnetic and dielectric behavior. Stoichiometric mixtures of Bi2O3, Fe2O3 and SrO were mixed and milled for 5?h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powder were pressed at 900?MPa to obtain cylindrical pellets and sintered at 800?°C for 2?h. X-ray diffraction and Rietveld refinement were used to evaluate the effect of Sr2+ on the crystal structure. In addition, vibrating sample magnetometry (VSM) and dielectric tests were used for describing the multiferroic behavior. The results show that Sr-doped BiFeO3 particles present rhombohedral structure (R3c) characteristic of α-BiFeO3 when the doping is below 0.10?mol of Sr. Additionally, a gradual decrease in the amount of secondary phases with the increase of the amount of strontium is observed. For doping concentration higher than 0.15?mol of Sr, a phase transition to an orthorhombic symmetry (β-BiFeO3, Pbnm) is detected. Besides, changes in relative intensities of reflection peaks planes (110) and (104) are associated with the phase transformations and with the magnetic and dielectric behavior. The α-BiFeO3 phase show antiferromagnetic behavior and high values of dielectric permittivity, whereas the β-BiFeO3 phase show a ferromagnetic behavior and low dielectric permittivity.  相似文献   

5.
《Ceramics International》2016,42(9):10808-10812
The structural, magnetic, and dielectric properties of the Y1−xHoxFe0.5Cr0.5O3 (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho3+ doped YFe0.5Cr0.5O3 samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho3+ and the canted Cr3+/Fe3+ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.  相似文献   

6.
The structural, electrical, magnetic and 57Fe Mössbauer studies of sol-gel synthesized polycrystalline Pr1-xAlxFeO3 (x?=?0, 0.1, 0.2, 0.3, 0.4 and 0.5) samples are reported in this paper and the phase purity of the materials was confirmed from Rietveld refinement of XRD pattern. From the magnetization studies it is observed that the Al doping at Pr site changed the magnetic ordering of the system at both room and low temperatures. The observed isomer-shift values from room temperature Mössbauer spectroscopy confirmed the charge state of the Fe ions and magnetic ordering in the compounds. Leakage current is observed to decrease with Al doping in the present work. From the leakage current density (J-E) measurements, it is observed that the space charge limited conduction (SCLC) dominates the conduction in lower and higher field regions for all the samples.  相似文献   

7.
《Ceramics International》2015,41(8):9285-9295
Rare earth Sm substituted Bi1−xSmxFeO3 with x=0, 0.025, 0.05, 0.075 and 0.10 polycrystalline ceramics were synthesized by a rapid liquid phase sintering method. The effect of varying composition of Sm substitution on the structural, dielectric, vibrational, optical and magnetic properties of doped BiFeO3 (BFO) ceramics have been investigated. X-ray diffraction patterns of the synthesized rare earth substituted multiferroic ceramics showed the pure phase formation with distorted rhombohedral structure with space group R3c. Good agreement between the observed and calculated diffraction patterns of Sm doped BFO ceramics in Rietveld refinement analysis of the X-ray diffraction patterns and Raman spectroscopy also confirmed the distorted rhombohedral perovskite structure with R3c symmetry. Dielectric measurements showed improved dielectric properties and magnetoelectric coupling around Néel temperature in all the doped samples. FTIR analysis establishes O–Fe–O and Fe–O stretching vibrations in BiFeO3 and Sm-doped BiFeO3. Photoluminescence (PL) spectra showed visible range emissions in modified BiFeO3 ceramics. The magnetic hysteresis measurements at room temperature and 5 K showed the increase in the magnetization with the increase in doping concentration of Sm which is due to the structural distortion and partial destruction of spin cycloid caused by Sm doping in BFO ceramics.  相似文献   

8.
In this study, Sm3+ doped Na0.5La0.5Bi8-xSmxTi7O27 (NBT-BITL-xSm, x = 0, 0.01, 0.015, 0.02, and 0.03) ceramics were synthesized via a conventional solid-state reaction process. The structural, electrical, and photoluminescence properties of NBT-BITL-xSm ceramics were systematically investigated. The crystal structure of NBT-BITL-xSm was refined using XRD Rietveld refinement and found to possess a single orthorhombic structure at room temperature. Raman spectroscopy revealed that Sm3+ ions preferred to substitute for Bi3+ located in the A-sites of pseudo-perovskite layers, inducing a slight decrease in orthorhombic distortion. Strong characteristic emission peaks of Sm3+ ions were observed in orange-red regions under a 407 nm laser source, and the sample with x = 0.015 achieved the optimal photoluminescent property. Dielectric measurements showed double anomaly permittivity peaks at the temperature of 589 and 600°C (Tm and Tc, respectively). The complex impedance spectrum indicated that the electrical conductivities mainly originated from crystal grains at high temperature. The activation energy was calculated to be 1.37–1.44 eV from Arrhenius fitting results. After Sm3+ substitution, the activation energy for conductivity was increased as a result of reduced oxygen vacancies.  相似文献   

9.
Ceria-based solid electrolytes exhibit superior electrical conductivity compared to traditional yttria-stabilized zirconia ceramics. However, they require high sintering temperatures to achieve full densification. Transition metal oxides exhibiting low melting points, such as CuO, have been used as additives to lower the sintering temperature of these materials. In this context, the present work is focused on the evaluation of the effects of gadolinium oxide (Gd2O3) content on the structure, densification and electrical properties of ceria co-doped with CuO. Nominal compositions of Ce0.99?xGdxCu0.01O2-δ (0 ≤ x ≤ 0.3) were synthesized by the polymeric precursor method. The precursor powders were characterized by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) and the calcined powders were studied by X-ray diffraction (XRD) and Rietveld refinement to obtain crystallographic parameters. The sinterability of green bodies was evaluated by dilatometry up to 1200 °C. The relative density was determined in samples sintered between 950 and 1050 °C and the microstructural characterization was performed by scanning electron microscopy (SEM). The electrical properties were investigated by impedance spectroscopy (IS). The XRD results confirms the formation of a cubic fluorite type structure in the entire composition range. The lattice parameters obtained by Rietveld refinement showed a reduction in the crystallite size with increasing gadolinium content. Densification was improved with increasing Gd-content up to x = 0.15. The electrical conductivity was enhanced by gadolinium addition, reaching a maximum of 7.81 mS cm?1 at 600 °C for the composition x = 0.15 sintered at a temperature as low as 1050 °C.  相似文献   

10.
《Ceramics International》2020,46(17):27336-27351
Present study highlights the influence of Ni doping on the structural, optical, dielectric, ferroelectric and magnetic properties of nanocrystalline BaTi1-xNixO3 (0 ≤ x ≤ 0.06) ceramics synthesized by sol-gel auto combustion process. Phase identification and crystal structure are examined through Rietveld refinement analysis that ensures mono-phase nature with tetragonal crystal structure in P4mm space group. The observed variation in the structural parameters viz. lattice constants, unit cell volume, bond lengths (Ti-O) and bond angles (Ti-O-Ti) are the direct evidence of distortion produce in the unit cell under the effect of Ni doping. The FTIR studies confirm perovskite structure and presence of stretching/bending vibrations of the various bands present in the samples. The optical properties divulge a minor alteration in optical bandgap under the influence of Ni content. Dielectric studies reveal higher value of the dielectric constant for pristine sample in the low frequency region, but its value decreases on Ni doping. The dielectric response, analyzed through UDR model, exhibits deviation from linear behavior at higher frequencies. Ferroelectric measurements demonstrate that the pristine sample has higher values of remnant polarization (Pr) and maximum polarization (Pm) which decrease linearly with the increase in Ni doping. Magnetic hysteresis loops at room temperature establish a weak ferromagnetic nature of the samples that arises due to the carrier-mediated exchange interactions with smaller values of magnetic parameters. These investigations ensure that the ferromagnetism can be induced in BaTiO3 by appropriate doping of Ni ions, which may find their potential use in the field of multiferroics.  相似文献   

11.
Cr and Co doped Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics were produced by solid state mixing of oxides. Cr and Co were doped into the Nb and Nb-Zn sites considering the compositions of Bi1.5Zn0.92Nb1.5−xCrxO6.92−x, (Bi1.5Zn0.46)(Zn0.46−3x/6Nb1.5−3x/5Crx)O6.92−x/2 for Cr doping and Bi1.5Zn0.92Nb1.5−3x/5CoxO6.92, (Bi1.5Zn0.46)(Zn0.46−3x/6Nb1.5−3x/5Cox)O6.92−x/2 for Co doping. The solubility limit of Cr in BZN was higher than that of Co and the solubility limit increased when doping was made both into Nb and Zn sites. The second phases appeared when x > 0.2 for Cr and x > 0.15 for Co doping into the Nb-Zn sites. Simultaneous Cr doping into the Nb- and Zn-sites of BZN pyrochlore gave higher dielectric constant than doping into the Nb-site of pyrochlore. However, Co doping into the Nb- and Zn-sites and only into the Nb-site of BZN gave identical dielectric results in the range of 202-218. The temperature coefficient of dielectric constant decreased with Cr doping and increased with Co doping.  相似文献   

12.
《Ceramics International》2020,46(7):8730-8744
We have studied the structural, magnetic, dielectric and impedance properties of the Sm1-xBixFe1-yMnyO3 [SmFeO3 (SFO), Sm0.9Bi0.1FeO3 (SBFO), Sm0.9Bi0.1Fe0.9Mn0.1O3 (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe3+-Fe3+ interactions due to the presence of Mn3+ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~103-104 with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.  相似文献   

13.
In order to study the effect of Sr substitution on structural and dielectric properties of Bi1−xSrxMnO3 (0.40≤x≤0.55) compounds were synthesized by the solid state reaction method. The as-prepared samples were characterized by X- ray diffraction (XRD) and dielectric measurements to correlate structural changes with dielectric properties. The XRD data were further analyzed by the Rietveld refinement. The highest dielectric constant was observed in Bi0.55Sr0.45MnO3 and Bi0.5Sr0.5MnO3 systems (∼106) mainly because of orientation polarization. The charge ordering temperature decreases with increasing Sr concentration in Bi1−xSrxMnO3 systems.  相似文献   

14.
Dy substituted CCTO ceramics were synthesized using solid state reaction method. Effect of Dy on structural, microstructural, dielectric and electrical properties has been studied over a wide temperature (300–500 K) and frequency range (100 Hz–1 MHz). Rietveld refinement, carried out on the samples, confirmed single phase formation and indicated overall decrease in lattice constant. Microstructure showed bimodal distribution of grains in CCTO with bigger grains surrounded by smaller grains. Dy substitution reduced grain size. Dy substitution in CCTO reduces the dielectric constant which may be attributed to increase of the Schottky potential barrier. The dielectric constant remains nearly constant in temperature range 300–400 K. The AC conductivity obeys a power law, σac=A fn, where n is the temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions, over entire temperature range, depending on conduction processes. The relevant charge transport mechanisms have been discussed.  相似文献   

15.
Using citrate sol-gel method, we prepared La0.85Mg0.15-xBaxFeO3(x?=?0.02–0.12) samples. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) were used to investigate whether the microstructure, composition, and magnetic properties of LaFeO3 were affected by the following parameters: calcination temperature, calcination time, and the doping concentration of Mg2+ ion and Ba2+ ions. The XRD spectra showed that a trace of impurity phase (MgFe2O4) is visible when the content of Mg2+ ions was higher; however, there was no change in the orthorhombic perovskite structure of LaFeO3 even at higher doping concentrations. The space group was still Pnma. No other phase was generated in the sample subjected to low-temperature calcination. Furthermore, FT-IR spectra confirmed the presence of some functional groups in the sample. Then, SEM showed that the size distribution of the particles is uniform in the sample, and the grain boundary is also clear. Finally, VSM measurements proved that the significant changes were produced in the magnetic properties of samples when they were doubly doped with Mg2+ and Ba2+ ions. Moreover, calcination temperature has a great influence on the magnetic properties of the samples.  相似文献   

16.
Gd doped Bi1-xGdxMn2O5 (x = 0.00–0.12) ceramics are synthesized via solid state reaction technique and they have been investigated for their structural, morphological, magnetic and electric properties. X-ray diffraction experiments and their corresponding Rietveld refinement confirm that the major phase characteristics of all the compositions are orthorhombic. The morphological studies reveal that the average grain size gradually decreases from 500nm to 200nm due to Gd substitution. The temperature dependent zero field cooled (ZFC) and field cooled (FC) magnetization curves demonstrate an antiferromagnetic Néel transition at 42 K. Due to the substitution of 4% Gd, the phase transition remains unaltered, however, both ZFC and FC curves coincide with each other at an applied magnetic field of 500 Oe. The remanent magnetizations and coercive fields are also found to enhance at room temperature due to the substitution of Gd. The polarization vs. electric field hysteresis loops exhibits the ferroelectric behavior of Bi1-xGdxMn2O5 (x = 0.00–0.12) ceramics at room temperature. Gd substitution also results in enhanced stability of the dielectric constant at wide range of high frequencies with significant suppression of low frequency dispersion particularly for 12% Gd doping. Moreover, a correlation among leakage current, remanent polarization, dielectric constant and microstructure has also been observed while investigating the Gd doped BiMn2O5 ceramics.  相似文献   

17.
Upper and lower solubility limits in Ba6−3xSm8+2xTi18O54 tungsten bronze ceramics were determined by Rietveld refinement of XRD data combined with backscattered electron images, and the variation tendency of microwave dielectric characteristics was also investigated. The upper solubility limit was confirmed as x = 2/3, while the lower solubility limit was determined as 1/4 instead of the previously reported one x = 3/10. The dielectric constant of Ba6−3xSm8+2xTi18O54 ceramics decreases monotonically with increasing x, while the small temperature coefficient of resonant frequency with complex variation tendency is observed for the compositions 1/2 ≤ x ≤ 4/5. The Qf value increases at first, reaches the maximum around x = 2/3, and turns to decrease for x > 7/10.  相似文献   

18.
《Ceramics International》2022,48(10):13780-13793
In this work, Bi3+ doped Ba0.98-3x/2BixCa0.02Zr0.02Ti0.976Cu0.008O3 [0 ≤ x ≤ 0.03] lead free ceramics, to be employed for structural, dielectric and ferroelectric studies, have been synthesized via conventional solid state reaction method. Rietveld refinement of the X-ray diffraction (XRD) data evidences the existence of a pure perovskite phase with tetragonal symmetry for all ceramics. The Scanning Electron Microscopy (SEM) reveals that the grain size, which is 16.14 μm for x = 0 reduced to 2.11 μm for x = 0.03. Dielectric studies demonstrate excellent dielectric behavior with high Curie temperature (TC ~159 °C), high dielectric constant (εr ~834, εmax ~ 3146), and a low dielectric loss (tanδ ~ 0.019), for an optimum value of x = 0.02. The analysis of temperature coefficient of the dielectric permittivity indicates the applicability of these materials in multilayer ceramic capacitors. Impedance studies, conducted to understand the underlying physical mechanisms, are found to be in good agreement with the results of structural and dielectric studies. Furthermore, the ferroelectric measurement confirms the ferroelectric nature for all samples with an energy storage efficiency (η) of ~42% for x = 0.02 composition.  相似文献   

19.
Bulk ceramic samples of BiFeO3 were light doped (up to 1%) with Nb5+ in the place of Fe3+ (B-site doping) and their multiferroic properties were investigated using XRD, SEM, polarization (PMTS) and magnetization (SQUID) techniques. It is shown that even the small percentages of doping can notably change electric and magnetic behavior. Electric conductivity differs by two orders of magnitude between samples doped with 0.2% and 1% Nb. The ferroelectric behavior strongly depended on conduction mechanism, and transition from space-charge-limited current (SCLC) conduction to trap-filled limited (TFL) conduction regime reflected on a change in hysteresis patterns, particularly for the samples with 0.2% and 0.5% Nb. Separation of ZFC-FC magnetization curves occurred for all Nb concentrations and increased with Nb doping. Weak ferromagnetic behavior and the increase of remnant magnetization with Nb concentration was observed from the hysteresis measurements. Coercive field changed drastically compared to the pure BiFeO3, namely, the sample with 1% Nb exhibited very high coercive magnetic field of ~ 10?kOe.  相似文献   

20.
The phase composition, microstructure, microwave dielectric properties of (Al0.5Nb0.5)4+ co-substitution for Ti site in LiNb0.6Ti0.5O3 ceramics and the low temperature sintering behaviors of Li2O-B2O3-SiO2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li1.075Nb0.625Ti0.45O3 solid solution was formed in all component. The increase of dielectric constant (εr) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τf value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb0.6Ti(0.5-x)(Al0.5Nb0.5)xO3 ceramics (x?=?0.10) when sintered at 1100?℃ for 2?h: εr =?70.34, Q×f =?5144?GHz, τf =?4.8?ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x?=?0.10 were obtained with 1.0?wt% glass: εr =?70.16, Q×f =?4153?GHz (at 4?GHz), τf =?-0.65?ppm/℃ when sintered at 925?℃ for 2?h.  相似文献   

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