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1.
《Ceramics International》2015,41(4):5531-5536
In this study, we investigated the effects of substituting Mn3+ for some Fe3+ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMnxFe2−xO4, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λS), about −167 ppm, and the CoMn0.2Fe1.8O4 sample exhibited the highest strain sensitivity (|dλ/dH|m) of 2.23×10−9 A−1m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.  相似文献   

2.
《Ceramics International》2017,43(17):14807-14812
Praseodymium substituted nano-crystalline Li-Ni spinel ferrites with different Pr3+ contents were synthesized by micro-emulsion method. X-ray diffraction (XRD), scanning electron spectroscopy (SEM) and vibrating sample magnetometery (VSM) techniques were employed to study the impact of substitution of the Pr3+ on the structure, surface morphology and magnetic parameters. XRD confirmed the formation of the single phase spinel ferrites of all compositions of LiNi0.5PrxFe2−xO4 nanocrystallites. The crystallite size determined from XRD data by Scherrer formula was calculated in range from 40 nm to 70 nm. However the nanoparticles size estimated by SEM was found 35–115 nm. The room temperature VSM measurements were carried out in the applied field range from “−10,000 Oe” to “10000” Oe. Saturation magnetization (MS) (41 emu/g) and coercivity (HC) values (156.9 Oe) of LiNi0.5Fe2O4 were improved by the addition of rare earth Pr3+ cations. The value of Hc is low, which is a strong indication of soft ferrites. The synthesized LiNi0.5PrxFe2−xO4 ferrites may be utilized for low core losses on transformers.  相似文献   

3.
《Ceramics International》2016,42(13):14475-14489
Sol-gel auto-combustion route using sucrose as fuel has been employed to synthesize nanocrystalline particles of SrZrxCoxFe(12−2x)O19 (0.0≤ x ≤1.0). The characterization of these materials has been done by TGA-DTA, FT-IR, XRD and EDS. SEM and TEM techniques have been used to study the structure and morphology. Magnetic properties have been investigated by VSM and Mössbauer spectroscopy (MS). The influence of calcination temperature on morphology and magnetic properties of samples is studied in a wide temperature range of 500–1100 °C. XRD analysis indicates the formation of pure single phase hexagonal ferrites at 900 °C. The crystallite size calculated using Scherrer equation lies in a narrow range of 21–33 nm. The crystallite size is small enough to obtain a suitable signal to noise ratio in high density recording medium. Substitution of Zr and Co for Fe has been found to have a profound effect on the structural, magnetic and electrical properties. Upon substitution saturation magnetization (MS) first increases from 62.67 emu/g to 64.84 emu/g (up to x=0.4) followed by a decrease to 49.71 emu/g at x=1.0. There is a slow fall in coercivity (HC) from 5785.74 (x=0.0) to 1796.51 Oe (x=1.0). Dielectric constant, dielectric loss tangent and AC conductivity in the frequency range 20 Hz to 120 MHz have been studied for all the compositions (x=0–1.0). The composition and frequency dependence of these dielectric parameters has been qualitatively explained.  相似文献   

4.
The morphological, compositional, structural, dielectric and electrical properties of Bi1.5Zn0.92Nb1.5?xSnxO6.92?x/2 ceramics have been investigated by means of scanning electron microscopy (SEM), X-ray energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), temperature and frequency dependent dielectric constant and temperature dependent conductivity measurements for Sn-contents in the range of 0.00  x  0.60. It was shown that single phase of the pyrochlore ceramics can only be obtained for x  0.25. Above this value a ZnO phase appeared in the XRD patterns and SEM micrographs as well. An increase in the lattice constant and in the temperature coefficient of dielectric constant and a decrease in the dielectric constant values with increasing Sn content was observed for the ceramics which exhibited a single phase formation. A temperature dependent but frequency invariant dielectric constant was observed for this type of ceramics. The lowest electrical conductivity and highest dielectric constant was observed for the sample which contains 0.06 Sn. The Bi1.5Zn0.92Nb1.5?xSnxO6.92?x/2 pyrochlore ceramic conductivities are thermally active above 395 K. For temperatures greater than 395 K, the conductivity activation energy which was found to be 0.415 eV for the pure sample increased to 1.371 eV when sample was doped with 0.06 Sn.  相似文献   

5.
A series of (1-x)(0.7Bi0.5Na0.5TiO3-0.3Bi0.2Sr0.7TiO3)-xNaNbO3 (BNT-BST-100xNN) lead-free ceramics were fabricated using conventional solid-state reaction technique. The phase behavior, microstructure, dielectric, ac impedance and energy-storage properties of the sintered ceramics were systematically investigated. XRD patterns and surface SEM micrographs revealed the introduction of NaNbO3 didn't change the perovskite structure of BNT-BST at low doping level. The NaNbO3 doping gave rise to slimmer P-E loops and thus gained enhanced energy storage properties. Therefore, a maximum energy storage density of 1.03 J/cm3 was achieved at 85 kV/cm at x = 0.01 via increasing the dielectric breakdown strength (DBS). Temperature-dependent dielectric permittivity illustrated the enhanced relaxor characteristics, implying the long-rang ferroelectric order was further damaged due to the introduction of NaNbO3. The results above indicate the sintered ternary ceramics can be a promising lead-free candidate for energy storage capacitors.  相似文献   

6.
《Ceramics International》2015,41(7):8578-8583
Gd1−xBixFe1−yZryO3 nanoparticles were synthesized via micro-emulsion route with different molar concentrations of Bi+3 (x) and Zr+4 (y). The values of x and y were kept in the range 0.00, 0.15, 0.30, 0.45 and 0.60. The characterizations were done by the thermo-gravimetric analysis (TGA), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The average particle size was ~50 nm. The effect of Bi3+ and Zr4+ contents on electrical, dielectric and magnetic parameters were studied. The DC resistivity measurements showed at certain Bi3+ and Zr4+ contents, more than two fold increase in electrical resistivity from 68×108 Ω cm to 150×108 Ω cm. The magnetic measurements showed the paramagnetic nature of Gd1−xBixFe1−yZryO3 nanoparticles. The electrical and magnetic properties of these nanoparticles suggested that these materials are potential candidates for the fabrication of telecommunication and switching devices.  相似文献   

7.
《Ceramics International》2017,43(2):2246-2251
Ultrahigh-Q Li2(1+x)Mg3ZrO6 microwave dielectric ceramics were successfully prepared by means of atmosphere-controlled sintering through simultaneously adopting double crucibles and sacrificial powder. This technique played an effective role in suppressing the lithium volatilization and further promoting the formation of the liquid phase, as evidenced by the X-ray diffraction, microstructural observation and the density measurement. Both dense and even microstructure, and the suppression of detrimental secondary phases contributed to low-loss microwave dielectric ceramics with Q×f values of 150,000–300,000 GHz. Particularly, desirable microwave dielectric properties of εr=12.8, Q×f=307,319 GHz (@9.88 GHz), and τf=−35 ppm/°C were achieved in the x=0.06 sample as sintered at 1275 °C for 6 h.  相似文献   

8.
《Ceramics International》2016,42(9):10801-10807
The Ba1−xSrxMg2V2O8 (0≤x≤0.4) microwave dielectric ceramics were fabricated by a standard solid-state reaction method. The formation of a continuous solid solution within the whole composition range was identified. The ceramic samples could be well densified in the temperature range of 885–975 °C in air for 4 h. The permittivity εr was found to increase with increasing ionic polarizabilities. The Q×f values were believed to be closely related with packing fraction and grain refinement. The Sr2+ substitution contributed to a monotonous increase of the A-site bond valence, such that the τf value experienced a considerable variation from negative to positive values. The optimum microwave dielectric properties of an εr of 13.3, a high Qxf of 86,640 GHz (9.6 Hz) and a near-zero τf of −6 ppm/°C could be yielded in the x=0.15 sample when sintered at 915 °C for 4 h.  相似文献   

9.
《Ceramics International》2016,42(8):9830-9835
This is the first report ever on (Mn2+–Zr4+) doped M-type lanthanum strontium hexaferrite with general formula, Sr0.85La0.15(MnZr)xFe12−2xO19 where x=0.0, 0.25, 0.50, 0.75, and 1.0, prepared by citrate auto-combustion method. These ferrites were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDX) and Vibrating sample magnetometer (VSM). X-ray diffraction patterns show the formation of high purity hexaferrite phase without other secondary phases for all the synthesized samples. It was observed from magnetic hysteresis data that the coercive force is reduced from 5692.5 Oe to 1669.2 Oe with increase in doping contents but the net magnetization of the samples varies slightly from 60.6 to 55.2 emu/gm. High saturation magnetization (Ms), low coercivity (Hc) and remanence magnetization (Mr) values of these materials make them particularly suitable for data recording.  相似文献   

10.
《Ceramics International》2016,42(4):4748-4753
The effect of substitution of diamagnetic Al3+ and In3+ ions for partial Fe3+ ions in a spinel lattice on the magnetic and microwave properties of magnesium–manganese (Mg–Mn) ferrites has been studied. Three kinds of Mg–Mn based ferrites with compositions of Mg0.9Mn0.1Fe2O4, Mg0.9Mn0.1Al0.1Fe1.9O4, and Mg0.9Mn0.1In0.1Fe1.9O4 were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al3+ or In3+ ions in place of Fe3+ ions in Mg–Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg–Mn ferrites in the X-band. In this study, the In3+ substituted Mg–Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.  相似文献   

11.
《Ceramics International》2017,43(13):9778-9782
Structural, electromagnetic, and dielectric properties of Li0.4Fe2.4Zn0.2O4 lithium-zinc ferrite sintered by 2.4 MeV pulsed electron beam heating at 1050 °С for 2 h were investigated. The formation of ferrite with a single-phase cubic spinel structure was confirmed by X-ray diffraction analysis. The average grain size of ferrite ceramic was determined by SEM analysis and its value was 1.7 µm. The radiation-thermal sintered samples are characterized by a saturation magnetization of 67.8 emu/g, the Curie temperature of 508 °C, AC electrical resistivity of 2.4×104 Ω cm (at 25 °C). The frequency dependences of permittivity and the loss tangent were obtained in (20 – 2×106) Hz frequency range. The behavior of ε′ is characterized by high dispersion caused by relaxation polarization in the investigated frequency range. The results were compared to the LiZn ferrite characteristics sintered by traditional thermal heating.  相似文献   

12.
Lead free ferroelectric ceramics near the morphotropic phase boundary (MPB) of KxNa1?x(NbO3)/KNN system (where x=0.48, 0.50, 0.52) were synthesized in the single perovskite phase by the partial co-precipitation synthesis route. The compositional dependences of phase, structure and electrical properties were studied in detail. X-ray diffraction (XRD) study revealed the coexistence of orthorhombic and monoclinic structures in K0.50N0.50NbO3. SEM characterization of the sintered KNN ceramics revealed dense and homogeneous packing of grains. Room temperature (RT) dielectric constant (εr) ~648, dielectric loss (tan δ) ~0.05 at 100 kHz, a relatively high density (ρ) ~4.49 g/cm3, remnant polarization (Pr) ~11.76 μC/cm2, coercive field (Ec) ~9.81 kV/cm, Curie temperature (Tc) ~372 °C and piezoelectric coefficient (d33) ~71 pC/N observed in K0.50N0.50NbO3 suggested that it can be an important lead free ferroelectric material.  相似文献   

13.
《Ceramics International》2016,42(5):5650-5658
Copper substituted Fe3O4 nanoparticles (NPs) (CuxFe1−xFe2O4 (0.0≤x≤1.0)) were synthesized by polyol method and the effect of Cu2+ substitution on structural, magnetic and optical properties of Fe3O4 was investigated. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV–Visible spectroscopy and Vibrating sample magnetometer (VSM) were used to study the physical properties of the products. The room temperature (RT) magnetization (σH) curves revealed the superparamagnetic nature of the products. The extrapolated specific saturation magnetization (σs) decreases from 42.69 emu/g to 14.14 emu/g with increasing Cu content (x). The particle size dependent Langevin fit studies were applied to determine the magnetic particle dimensions (Dmag). The average magnetic particle diameter is about 9.89 nm. The observed magnetic moments of NPs are in range of (0.61–1.77) µB and rather less than 4 µB of bulk Fe3O4 and 1 µB of bulk CuFe2O4. Magnetic anisotropy was assigned as uniaxial and calculated effective anisotropy constants (Keff) are between 10.89×104 Erg/g and 26.95×104 Erg/g. The average value of magnetically inactive layer for CuxFe1−xFe2O4 NPs was calculated as 1.23 nm. The percent diffuse reflectance spectroscopy (DR%) and Kubelka–Munk theory were applied to determine the energy band gap (Eg) of NPs. The extrapolated optical Eg values from Tauc plots are between minimum 1.98 eV to 2.31 eV. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer splitting, quadrupole splitting and hyperfine magnetic field values on Cu+2 ion substitution have been determined. Although, the Mössbauer spectra for the sample x=0.2 and 0.8 are composed of paramagnetic doublets, ferromagnetic sextets were also formed for other products.  相似文献   

14.
《Ceramics International》2016,42(9):10664-10670
Nano crystalline Ni–Zn ferrites of composition Ni0.5Zn0.5Fe2O4have been prepared by a chemical co-precipitation method. The powdered samples were sintered at a temperature of 800 °C and 900 °C for three hours. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to study their structural and morphological changes. The enhanced magnetic properties were investigated by using a Vibrating Sample Magnetometer (VSM). The saturation magnetization was found to increase from 73.88 to 89.50 emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1 GHz. These results have been explained on the basis of various models and theories.  相似文献   

15.
《Ceramics International》2016,42(16):18357-18367
Microcrystalline samples of new Cd1–3xDy2xxMoO4 solid solution with limited homogeneity (0<x≤0.2222) and cationic vacancies (denoted as ⌷) were prepared by a high-temperature solid state reaction. The XRD data and SEM analysis showed that as-prepared ceramics crystallize in the tetragonal scheelite type symmetry (space group I41/a) with the crystallite size varying between ~2 and ~20 µm. A systematic change in lattice constants, a and c, as well as in lattice parameter ratio c/a with an increase of Dy content was observed. Dy-doped molybdates are paramagnets with the antiferromagnetic short-range interaction and spin-orbit coupling. Optical and electrical investigations proved Cd1–3xDy2xxMoO4 solid solution to be in the insulating state of Eg>3 eV at room temperature and the thermally activated conduction of the Arrhenius-type above 350 K. Moreover, the I-V characteristics provided the evidence of symmetrical and non-linear behavior typical of charge carrier emission weakly induced by the temperature. Relative dielectric permittivity εr below 10 as well as loss tangent tanδ below 0.15 do not substantially depend both on the temperature in the range of 76–400 K and the frequency in the range of 5·102–1·106 Hz. These results are interpreted in the framework of the acceptor and donor vacancy centers.  相似文献   

16.
《Ceramics International》2016,42(7):8627-8635
Single-phase M-type hexagonal ferrites, SrBixFe12−xO19 (0.0≤x≤1.0), were prepared by a co-precipitation assisted ceramic route. The influence of the Bi3+ substitution on the crystallization of ferrite phase has been examined using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Mössbauer spectroscopy. The XRD data show that the nanoparticles crystallize in the single hexagonal magnetoplumbite phase with the crystallite size varying between 65 and 82 nm. A systematic change in the lattice constants, a=b and c, was observed because of the ionic radius of Bi3+ (1.17 Å) being larger than that of Fe3+ ion (0.64 Å). SEM analysis indicated the hexagonal shape morphology of products. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Bi substitutions have been determined.  相似文献   

17.
《Ceramics International》2016,42(4):5218-5225
The synthesis of a material having ferroelectric and ferromagnetic properties in the same phase is a challenging task. In the present work, lanthanum based multiferroic materials, with composition La1−xCoxFe1−yNiyO3 (where, x=0.0–0.5 and y=0.0–1.0), have been synthesized via sol–gel auto-combustion method. The phase of the synthesized materials was confirmed by the X-ray diffraction (XRD) analysis, while the surface morphology and particle size were determined by the scanning electron microscopy (SEM) analysis. The DC electrical resistivity and activation energy were observed to increase from 2.14×107 to 3.04×1010 Ω cm and 0.64 to 0.77 eV, respectively with the increase in concentration of substituents. The drift mobility decreases from 3.27×10−13 to 2.80×10−16 cm2 V−1 S−1. The dielectric constant, dielectric loss and dielectric loss factor decrease with the increase in frequency (1 MHz to 3 GHz) and Ni–Co content as well. The electrical and dielectric results are in good agreement with each other. The increase in electrical resistivity and decrease in dielectric parameters make these materials suitable for applications in microwave devices.  相似文献   

18.
《Ceramics International》2016,42(4):4754-4763
Manganese substituted nickel ferrites, Ni1−xMnxFe2O4 (x=0, 0.3, 0.5 and 0.7) have been obtained by a combined method, heat treatment and subsequent mechanical milling. The samples were characterised by X-ray diffraction, differential scanning calorimetry and magnetic measurements. The increase of the Mn2+ cations amount into the spinel structure leads to a significant expansion of the cubic spinel structure lattice parameter. The crystallite size decreases with increasing milling time up to 120 min, more rapidly for the nickel–manganese ferrites with a large amount of Mn2+ cations (x=0.7). After only 15 min of milling the mean crystallites size is less than 25 nm for all synthesised ferrites. The Néel temperature decreases by increasing Mn2+ cation amount from 585 °C for x=0 up to 380 °C for x=0.7. The magnetisation of the ferrite increases by introducing more manganese cations into the spinel structure. The magnetisation of the milled samples decreases by increasing milling time for each ratio among Ni and Mn cations and tends to be difficult to saturate, a behaviour assigned to the spin canted effect.  相似文献   

19.
《Ceramics International》2016,42(3):4176-4184
The effect of the La3+ and Gd3+ co-doping on the structure, electric and magnetic properties of BiFeO3 (BFO) ceramics are investigated. For the compositions (x=0 and 0≤y≤0.15) in the perovskite structured LaxGdyBi1−(x+y)FeO3 system, a tiny residual phase of Bi2Fe4O9 is noticed. Such a secondary phase is suppressed with the incorporation of ‘La’ content (x). The magnitude of dielectric constant (εr) increases progressively by increasing the ‘La’ content from x=0 to 0.15 with a remarkable decrease of dielectric loss. For x=0.15, the system LaxGdyBi1−(x+y)FeO3 exhibits highest remanent magnetization (Mr) of 0.18 emu/g and coercive magnetic field (HC) of ~1 T in the presence of external magnetic field of 9 T at 300 K. The origin of enhanced dielectric and magnetic properties of LaxGdyBi1−(x+y)FeO3 and the role of doping elements, La3+, Gd3+ has been discussed.  相似文献   

20.
《Ceramics International》2015,41(7):8367-8376
In this study, (1−x)[0.6Pb(Mg1/3Nb2/3)O3–0.4Pb(Zr0.52Ti0.48)O3]–xBa(Zn1/3Nb2/3)O3; (1−x)PMNZT60/40–xBZN having x=0, 2.5, 5, 7.5, and 10 mol% ceramics were prepared by mixed oxide powder method and sintered using a two-step process. Phase transitions were investigated by XRD, microstructure by SEM, crystal morphology by TEM, the dielectric and ferroelectric properties by capacitance measurement setup and modified Sawyer-Tower circuit, respectively. The dielectric constant and dielectric loss tangent were measured as functions of both temperature and frequency. The XRD results show the phase transition from tetragonal phase to pseudo-cubic phase with addition of BZN in PMNZT system. Grain size of about 1.23–2.42 μm and crystallite size in a range of 421–2152 nm were obtained. The pure-phase 0.6PMN–0.4PZT ceramics show the normal ferroelectric behavior. The 0.95(PMNZT60/40)–0.05BZN and 0.925(PMNZT60/40)–0.075BZN showed a broad and diffused dielectric properties and the dispersive phase transition, indicating the relaxor ferroelectric behavior. The transition temperature in the BZN-modified PMNZT system is seen to decrease from 166 °C in pure PMNZT60/40 to 102 °C and 54 °C with increasing BZN content to 5 and 10 mol%, respectively. In addition, the maximum dielectric constant is decreased with increasing BZN content. The PE hysteresis loop measurements show the change from the normal ferroelectric behavior in PMNZT60/40 ceramic to more relaxor behavior that was induced with BZN addition. These results clearly demonstrated the significance of BZN to the electrical responses of the PMNZT60/40 system.  相似文献   

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