Effects of copper content on the structural and magnetic properties of spinel (Co,Cu)Fe2O4 ferrites

Spinel Co–Cu ferrites with the nominal composition Co_1?x Cu _x Fe₂O₄ ferrites (x = 0.0–0.4 with steps of 0.1) were prepared by a chemical coprecipitaiton and sintering process, and their structural and magnetic properties were studied by using XRD, TGA–DTA, FTIR, SEM and VSM analyses. All the specimens prepared are single phase after sintering at 900 °C for 5 h, and nearly no change of lattice parameter is found. The study of grain size shows that suitable amount of Cu substitution is favorable for the growth of grains, while too much Cu substitution inhibits the growth of grains instead. Also found is that with the increase of x, the saturation magnetization decreases continuously from 76.6 (x = 0.0) to 59.0 emu/g (x = 0.4), while the coercivity exhibits a first decreasing but then increasing tendency.     

X-Ray Pole Figure Analysis and Magnetic Properties of Microwave Sintered Sr-M-type Hexagonal Ferrites

Sr-M-type sintered hexagonal ferrites were prepared by the conventional and microwave sintering method. X-ray diffraction and pole figure analysis, scanning electron microscopy (SEM), and Robograph 2 magnetic properties test instrument were applied to character the structure and magnetic properties of sintered ferrites. The XRD results reveal all the sintered samples are composed of SrFe₁₂O₁₉ single phase with obvious c-axis alignment. The sample with MS treatment at 1050 ^°C exhibits the optimum magnetic alignment, showing the optimum (0?0?8) and (1?0?7) pole figures with almost all circular lines focused on the center and at about 30^° of α, respectively. Few pores and optimal densification characters can be seen from the SEM image of strontium ferrites microwave sintered at 1050 ^°C, resulting in the optical magnetic properties as remanence (B _r) of 410.5 mT, coercivity (H _cj) of 372.2 kA/m, and maximum magnetic energy product ((BH)_max) of 31.53 kJ/m³, respectively.     

Structural and magnetic properties of spinel (Co,Cu)Fe2O4 ferrites prepared via a hydrothermal and sintering process

Spinel Co–Cu ferrites with the nominal composition Co_1?x Cu _x Fe₂O₄ ferrites (x = 0.0–0.4 with steps of 0.1) were prepared by a hydrothermal and sintering process, and the structural and magnetic properties of as-synthesized and sintered powder specimens were compared by using X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry and vibrating sample magnetometer analyses. It is found that all the as-synthesized and sintered specimens are single phase, and only suitable amount of Cu²⁺ substitution (x ≤ 0.3) is favorable for the growth of grains at high sintering temperature. In addition, with the increase of x, the saturation magnetization of both the as-synthesized and sintered powders decreases continuously, while the coercivity exhibits a first increasing but then decreasing tendency.     

Phase stability, low temperature cofiring and microwave dielectric properties of BaTi5O11 ceramics with BaCu(B2O5) addition

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature, microstructure and microwave dielectric properties of BaTi₅O₁₁ modified with 1.0 wt% CuO (BTC) ceramic have been investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The BTC ceramic shows a high sintering temperature (~1,100 °C) and good microwave dielectric properties as Q × f = 44,530 GHz, ε _r = 40.5, τ _f  = 39 ppm/°C. The addition of BCB to BTC effectively reduced the sintering temperature from 1,100 to 925 °C. The reduced sintering temperature was attributed to the BCB liquid phase. The BTC ceramic doped with 4 wt% BCB has a good microwave dielectric properties with Q × f = 25,502 GHz, ε _r = 37.4, τ _f  = 33.1 ppm/°C. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

Appreciable Magnetic Moment and Energy Density in Single-Step Normal Route Synthesized MnBi

We study the structural and magnetic properties of the MnBi intermetallic compound. The LTP (Low Temperature Phase) MnBi compound is successfully synthesized in single step by vacuum encapsulation technique and rapid quenching from phase formation temperature. The phase purity and the magnetic moments of MnBi are highly dependent on heat treating schedule. The best phase purity and the magnetic moment are found for a heat-treated sample at 310 °C for 48 h. Rietveld fitted X-ray diffraction (XRD) patterns revealed that the studied MnBi compound is crystallized in hexagonal P63/mmc space group with minute presence of unreacted Bi and Mn phases. The scanning electron microscopy (SEM) study is carried out to visualize the grains morphology and phase identification. The bulk MnBi powder showed appreciable magnetic moment of ～62 emu/g at 6 Tesla and maximum energy product BH _max of 4.01 MGOe at 6 Tesla. The magnetic properties of synthesized MnBi show that it could be a potential candidate for rare earth free permanent magnets.     

High performance sintering NiCuZn ferrites absorber sheet for HF application

By using a new and simple blade casting method, a lighter, thinner and higher absorption property sintering NiCuZn ferrite electromagnetic wave absorber sheet was first demonstrated. The electromagnetic wave absorption ability was enhanced by sintered NiCuZn ferrite absorbent. The experiment results reveal that NiCuZn ferrite with thickness 0.1 mm absorber sheet achieves its maximum reflection loss value above 0.5 dB at 13.46 MHz. Meanwhile, the absorption bandwidth is larger than 1 MHz is profitable for wideband electromagnetic wave absorbing. The absorption properties could be controlled by the variation of Nickel content in the spinel lattice and the sintering temperature of NiCuZn ferrites. More homogenous microstructure of SEM micrograph and better crystalline XRD pattern may be responsible for the best absorption ability at 1,150 °C sintering temperature. The absorption properties were also successfully analyzed in this work, which took into account both the frequency at the reflection loss minimum (f _r) shift correlated with the value of inductance (L) and impedance (Z) of sintered toroidal cores and the power reflection loss (Γ) depending on ε″, μ″, and $\sqrt {\varepsilon \mu }$ , where ε and μ are complex relative dielectric permittivity and permeability, respectively, for the attenuation material. The sintering NiCuZn ferrites could merit to be potential candidates as electromagnetic attenuation materials to meet the demands for miniaturization, broader relative bandwidths at HF (3–30 MHz) and beneficial for fabrication of radio frequency identification metal tag.     

Effect of Sintering Temperature on the Microstructure,Electrical, and Magnetic Properties of Bi 0 . 8 5 Eu 0 . 1 5 FeO 3 Ceramics

Polycrystalline Bi _0.85Eu _0.15FeO ₃ ceramics were synthesized by solid-state reaction method with rapid liquid phase sintering process at various sintering temperatures. The dependence of structural, microstructural, electrical, and magnetic properties on sintering temperature was systematically investigated. X-ray diffraction measurements reveal that single perovskite phase is developed in Bi _0.85Eu _0.15FeO ₃ ceramics sintered at 850 and 870^° C, while secondary phases can be detected in the samples sintered at 890^° C due to the volatilization of Bi ³⁺ ions, and the crystallinity increases with increasing sintering temperature from 850 to 890 °C. The scanning electron microscopy investigation has suggested that the grain size increases with increasing sintering temperature from 855 t o 890^° C; while the pore size decreases with increasing sintering temperature from 850 to 870^° C and then increases with a further increase of sintering temperature. The electrical and magnetic measurements show that the leakage current, dielectric constant, dielectric loss, and magnetic properties are strongly dependent on the sintering temperature. The Bi _0.85Eu _0.15FeO ₃ ceramics sintered at 870^° C have the lower leakage current, higher dielectric constant, and lower dielectric loss. The room temperature magnetization increases with increasing sintering temperature from 850 to 890 °C. The possible reason for all the above observations was discussed.     

Improvement of the Nature of Indentation Size Effect of Bi-2212 Superconducting Matrix by Doped Nd Inclusion and Theoretical Modeling of New Matrix

Neodmium (Nd) inclusions at different stoichiometric ratios (x=0.0, 0.001 %, 0.005 %, 0.01 %, 0.05 %, 0.1 %) are doped in the Bi-2212 superconducting samples and the samples obtained are subjected to the sintering process at 840 ^°C constant temperature for 72 hours. The effect of Nd doping on the structural and mechanical properties of prepared samples is investigated by the standard characterization measurements. XRD and SEM measurements are performed to obtain information about surface morphology, phase ratios, lattice parameters and particle size. Moreover, Vickers microhardness (H _V ) measurements are exerted to investigate the mechanical properties of the all samples in detail. It is found that all the properties given above retrogress with the increase of the Nd concentration in the Bi-2212 superconducting core. However, the ISE nature of the materials improves systematically. Additionally, the experimental results of microhardness measurements are analyzed using Meyer’s law, PSR, MPSR, EPD models and HK approach. The results show that Hays–Kendall approach is determined as the most successful model.     

Structural Characterization and Magneto Electrical Behavior of Sm Doped La0.7Ca0.3MnO3 Manganites

The La_0.7?x Sm _x Ca_0.3MnO₃ with x=0.0 and 0.1 compounds were fabricated by compositional solid state reaction method and investigated for their structural and magnetoelectrical properties. The samples are characterized structurally by X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectrometer. The electrical and magnetotransport properties of bulk samples have been investigated in the temperature range 5–300 K and a magnetic field up to 7 T. The metal–insulator transition temperature, T _MI, decreased with samarium (Sm) doping and also it is increased slightly with the application of magnetic field. The results of Sm doped LCMO compound showed that the maximum magneto resistance (MR) is about 54 % and it appears near the transition temperature.     

Synthesis Pressure–Temperature Effect on Pinning in MgB2-Based Superconductors

The volume pinning force, F _p(max), increases with increasing synthesis or sintering pressure (0.1 MPa–2 GPa) in materials prepared at high temperature (1050 °C) while it stays practically unchanged in those prepared at low temperature (800 °C). The position of F _p(max) can be shifted to higher magnetic fields by: (1) increasing the manufacturing pressure or decreasing the temperature (2) additions (Ti, SiC, or C, for example), and (3) in-situ preparation. Grain boundary pinning (GBP) dominates in materials prepared at low temperatures (600–800 °C), while high-temperature preparation induces strong point pinning (PP) or mixed pinning (MP) leading to outstanding properties. In materials produced by spark plasma sintering (SPS), the position of F _p(max) is higher than expected for both grain boundary and point pinning. The distribution of boron and oxygen in MgB₂ based material, which can changed by additions or the preparation conditions, significantly affects the type and strength of pining. Materials prepared under a pressure of 2 GPa with a nominal composition of Mg:7B or Mg:12B consist of 88.5 wt % MgB₁₂, 2.5 wt % MgB₂, 9 wt % MgO or 53 wt % MgB₁₂, 31 wt % MgB₂₀ 16 wt % MgO, respectively. Their magnetic shielding fractions at low temperatures are 10 % and 1.5 %, with a transition temperature, T _c of 37.4–37.6 K. Although their magnetic critical current density at zero field and 20 K was 2–5×10² A/cm², they were found to be insulating on the macroscopic level.     

Low-temperature sintering and microwave dielectric properties of Li2TiO3 based ceramics

New low sintering temperature and temperature-stable low-loss ceramics based on Li₂TiO₃ with lithium zinc borate (LZB) glass and LiZnNbO₄ doping have been prepared by the conventional solid-state reaction route. The effect of LZB glass addition on the sinterability, phase purity, microstructure, and microwave dielectric properties of Li₂TiO₃ ceramics has been investigated. The XRD results suggest the presence of single Li₂TiO₃ phases for LZB glass-added Li₂TiO₃ ceramics. The addition of LZB glass can effectively lower the sintering temperature to 900 °C, and does not induce much degradation of the microwave dielectric properties. Typically, the 2.0 wt% LZB glass-added ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 23.2, Q × f = 38,909 GHz, and τ _f  = 30.1 ppm/°C. Meanwhile, LiZnNbO₄ compound is selected to tune the temperature coefficient of resonant frequency (τ _f ) to near zero. It is found that the 2.0 wt% LZB glass-added Li₂TiO₃ ceramics with 35 wt% LiZnNbO₄ sintered at 925 °C have good microwave dielectric properties of ε_r = 20.7, Q × f = 19,366 GHz, τ _f  = ?0.5 ppm/°C, which can find applications in microwave devices that require low sintering temperature.     

Effect of sintering temperature and time on microwave dielectric properties of CaNb2O6 ceramics

The microwave dielectric properties of CaNb₂O₆ ceramics were investigated with a view to their application in mobile communication. The CaNb₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures and sintering times. A maximum density of 4.67 g/cm³ was obtained for CaNb₂O₆ ceramic, sintered at 1,400 °C for 4 h. Dielectric constants (ε _r ) of 13.3–18.1 and quality factor (Q × f) of 12,200–50,000 GHz were obtained at sintering temperatures in the range 1,300–1,500 °C for 4 h. Dielectric constants (ε _r ) of 18.0–18.1 and quality factor (Q × f) of 44,300–50,000 GHz were obtained for sintering times in the range 2–6 h at a sintering temperature of 1,400 °C. A dielectric constant (ε _r ) of 18.1, a quality factor (Q × f) of 50,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?54 ppm/°C were obtained when CaNb₂O₆ ceramics were sintered at 1,400 °C for 4 h.     

Effect of Ni Doping on Structural,Morphological, Optical and Magnetic Properties of Zn1−x Ni x O Dilute Magnetic Semiconductors

Ni²⁺-doped ZnO diluted magnetic semiconducting materials (Zn_1?x Ni _x O with x=0.01,0.02,0.03,0.04,0.05) were synthesised by the co-precipitation method. All synthesised samples were sintered at 600 °C for 6 hours. The effects of Ni²⁺ ion-doping on the structural, morphological, optical and magnetic properties of ZnO were investigated using powder X-ray diffraction, field emission SEM, UV–DRS spectroscopy, photoluminescence and vibrating sample magnetometry. The XRD patterns of pure and Ni-doped ZnO samples revealed single phase hexagonal wurtzite structure. The SEM analysis revealed the morphology of prepared samples, and the chemical compositions of all samples were analysed using exhibit energy density X-ray analysis (EDAX) characterisation. The absorption and emission properties revealed the effect of Ni²⁺ doping in ZnO samples. All Ni²⁺ ion-doped samples showed ferromagnetism at room temperature. The observed results are here analysed and reported.     

Magnetic Phase-Transition Dependence on Nano-to-Micron Grain-Size Microstructural Changes of Mechanically Alloyed and Sintered Ni0.6Zn0.4Fe2 O 4

The microstructure evolution in several polycrystalline Ni_0.6Zn_0.4Fe₂O₄ samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. The Ni_0.6Zn_0.4Fe₂O₄ toroidal sample was prepared via mechanical alloying and subsequent molding; the sample with nanometer-sized compacted powder was repeatedly sintered from 600 to 1200 °C with an increment of 25 °C. An integrated analysis of phase, microstructural and hysteresis data pointed to existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism (Idza in Mater. Res. Bull. 47:1345–1352, 2012), respectively. The real permeability, μ′, and loss factor, μ″, increased with grain size which increased due to increase in sintering temperature and these two magnetic properties also seem to belong to three value-differentiated groups corresponding to the same temperature ranges found for the B–H groupings. These groupings are tentatively explained using Snoek’s Law.     

Grain growth,densification and electrical properties of lead-free piezoelectric ceramics from nanocrystalline (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 powder by sol–gel technique

The sintering behavior revealed in the sintering processes of the conventional and a two-step process and electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from the nanocrystalline powders synthesized by a sol–gel technique were systematically studied. It was found that the sintering process of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics made from nanocrystalline powders was significantly improved, the sintering temperature was reduced markedly from 1,540 to 1,280 °C, as well as a high relative density (>97 %) was obtained in the conventional sintering. Under the two-step sintering conditions, the full densification and the most suppression of grain growth was achieved simultaneously. The (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics from nanocrystalline powders sintered by the two-step sintering technique (sintered at T ₁ of 1,300 °C for 1 min and T ₂ of 1,150 °C for 20 h) exhibited the optimum average grain size of 700 nm and a high relative density of 98 %. The electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics were greatly influenced by the grain size and phase structure formed under the both sintering conditions, with sintering temperature and grain size increased, the electrical properties of the (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ ceramics, which made from nanocrystalline powders, shows an enhancing trend: d ₃₃ ~100 pC/N, k _p ~53.3 % for the specimen sintered at 1,300 °C for 1 min and 1,150 °C for 20 h, d ₃₃ ~310 pC/N, k _p ~53.3 % for the specimen sintered at 1,350 °C for 2 h respectively.     

Effects of sintering temperature on the properties of Mn/Y codoped Ba<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>TiO<Subscript>3</Subscript> ceramics for tunable application

(Ba_0.67Sr_0.33)_1?3x/2Y _x Ti_1?y/2Mn _y O₃ [BST(Mn + Y), x = 0.006, y = 0.005] ceramics were fabricated by using citrate–nitrate combustion derived powder. Microstructure and dielectric properties of the BST(Mn + Y) ceramic samples were investigated within the sintering temperature ranged from 1220 to 1300 °C. Sintering temperature has a great influence on the microstructure and electrical properties of the ceramic samples. The dielectric properties, ferroelectric properties, and tunability are enhanced by optimizing sintering temperature. The relatively high tunability of 40 % (1.5 kV/mm DC field, 10 kHz) was obtained, and relatively low dielectric loss, <0.0052 (at 10 kHz, 20 °C) was acquired for BST(Mn + Y) samples sintered at 1275 °C for 3 h. Both the low dielectric loss and enhanced tunable properties of BST(Mn + Y) are useful for tunable devices application.     

Microstructure and piezoelectric properties of NaF-doped K0.5Na0.5Nb0.95Ta0.05O3 lead-free ceramics

The effects of NaF on the microstructure and electrical properties of K_0.5Na_0.5Nb_0.95Ta_0.05 lead-free ceramics prepared by conventional sintering method were investigated in this study. The dopant NaF effectively lowers the sintering temperature and promotes the grain growth. Samples with a high relative density up to 96.3 % are achieved by adding 0.6 wt% NaF to improve the sinterability. The electric properties are also enhanced, and the optimum properties are achieved at the doping content of 1.0 wt% (d ₃₃ = 153 pC/N, k _P = 32.2 %, Q _m = 80.5, E _c = 0.89 kV/mm, and P _r = 16.5 μC/cm²). The improvement of ferroelectric and piezoelectric properties is suggested to be largely contributed to the compensation of sodium element from dopant NaF for the volatilization of A-site alkali elements.     

Microstructural and magnetic properties of self-biased strontium hexaferrite thick films by two-step sintering

SrFe₁₂O₁₉ hexaferrite thick films were prepared by tape casting method followed by a two-step sintering process. X-Ray diffractometer, field emission scanning electron microscope and vibrating sample magnetometer were used to investigate the microstructure and magnetic properties of samples. Results show that high density films with nanocrystalline grains, high crystallographic c-axis orientation of crystals perpendicular to the film plane with high squareness (M _r/M _s = 0.93) and moderate coercivity (H _c = 3,750 Oe) can be obtained with two-step sintering. Grains growth is controllable by this sintering method. The average grain size of the films strongly depends on final stage of sintering and quality of starting powders and ranging between 0.5 and 10 μm. The thick films with starting powders from coprecipitation method are denser with smaller grain size rather than those with starting powders from solid state reactions. This work reveals the feasibility of fabrication of thick hexaferrite films with a simple and effective method for next generation of self-biased planar microwave devices.     

ZnTiO3-based ceramics sintered at low temperature with boron addition for multilayer ceramic capacitor applications

Mixture of zinc metatitanate and rutile (ZnTiO₃ + 0.2TiO₂), had been prepared via the conventional solid-state reaction method. The sintering behavior and microwave dielectric properties of ZnO–TiO₂ system were investigated. The composition and microstructure of ceramics were discussed with XRD and SEM. It was found that ZnO–TiO₂ ceramics, which was sintered at 900°C using 1.0 wt% B₂O₃ as sintering additive, had homogeneously fine microstructures and high densification. Samples possessed excellent microwave dielectric properties: ε _r = 26, Q × f = 34,890 GHz, and τ _f = ?11 ppm/°C. The above- mentioned material was suitable for the tape casting process and compatible with Ag electrodes, therefore, was an excellent candidate for multilayer ceramic capacitor applications.