Increase Of Substitution Content Research Articles

Tuning of efficient energy storage and fast switching capability in La2Zr2O7 pyrochlore nanoparticles mediated by Gd-substitution

Electrostatic capacitors are widely investigated to fulfill the energy storage demand and their utilization in microelectronic devices. The efficient energy storage capabilities of pyrochlores with less loss factor make them eminent in energy storage contesters. Here we synthesized a series of La2-xGdxZr2O7 with x = 0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 substitution contents via the sol-gel auto-combustion process. The substitution of Gd on the La site compresses the pyrochlore structure without any phase transformation which leads to an increase in the X-ray density. A gradual decrease in grain size with an increase in substitution contents causes the increase in surface adhesion and agglomeration. Energy-dispersive X-ray spectra confirm the formation of exact compositions for all the samples. The energy storage capability of the synthesized series is examined by the PE loop, leakage current, PUND sequence, and normalized capacitance. An increase in energy storage abilities is noted with an increase in Gd concentration. The small value of energy loss, the highest recoverable energy density with a larger value of effective and normalized capacitance is recorded for Gd1.6La0.4Zr2O7 composition which exposed the potential of this composition for microelectronics devices to fulfill the energy storage demand.

Al3+ doped M-type hexagonal Ba–Co ferrites synthesized via ball-milling assisted ceramic process: magnetism and its correlation with structural properties

Ba0.5Co0.5AlxFe12−xO19 (x = 0, 0.08, 0.16, and 0.24) hexaferrites are synthesized via ball-milling assisted ceramic process, and their crystal structure, microstructure, and magnetic properties were studied. The results show that all samples, calcined between 950 and 1150 °C, consist of the main M-type hexagonal Ba ferrite phase in combination of a small amount of CoFe2O4 and Fe2O3 phase. The lattice parameters of M-type hexagonal Ba0.5Co0.5AlxFe12−xO19 decrease after Al3+ doping. The addition of Al3+ ions results in a reduction of crystallite size, which is attributed that the presence of foreign phase CoFe2O4 and Fe2O3 restrains the growth of the Ba0.5Co0.5AlxFe12−xO19 crystallite. Magnetic characterization indicates that all samples exhibit hard magnetic properties. Trend of specific saturation magnetization of Ba0.5Co0.5AlxFe12−xO19 sample, calcined at 1050 and 1150 °C, decreases with the increase in Al3+ content. The varied magnetic properties with substitution content (x) are well explained by the occupancy effects of Al3+ ions in magnetoplumbite structure. Ba0.5Co0.5Fe12O19, calcined at 1150 °C, has the highest specific saturation magnetization value (56.07 emu/g), remanence (28.66 emu/g), and moment (10.76 µB). Besides, with the increase of substitution content (x), magnetic domain type of ferrites, calcined at 1150 °C, changes from a single magnetic domain to a multi-domain type.

Microwave dielectric properties of Ba3.75Nd9.5Ti18−zCr4z/3O54 ceramics

The Ba3.75Nd9.5Ti18−z Cr4z/3O54 (0 ≤ z ≤ 3.0) ceramics were prepared using the solid-state reaction route. The influence of substitution of Cr for Ti on microstructure and microwave dielectric properties of Ba3.75Nd9.5Ti18−z Cr4z/3O54 (BNTCz) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that pure BaNd2Ti5O14 phase with tungsten bronze structure existed for z ≤ 1, but the secondary phase Ba4Ti12O27 was observed for 1.5 ≤ z ≤ 3. The substitution of Cr for Ti was confirmed by the results of scanning electron microscopy and energy dispersive spectrometer. The dielectric constant (e r ) was deteriorated with the increment of substitution which was in accord with the tendency of apparent density. The quality factor value (Q×f) was improved by a small amount of substitution for z ≤ 0.5, but deteriorated seriously when excessive Cr content was added (z > 0.5). The temperature coefficient of the resonant frequency (τ f ) was effectively reduced from + 63 ppm/°C to − 7.1 ppm/°C with the increase of substitution content. At last, the excellent dielectric properties with e r = 81.53, Q×f = 11,294 GHz and τ f = + 39.2 ppm/°C were obtained as z = 0.5 sintered at 1420 °C for 2 h.

Synthesis of hexagonal Co3+-substituted Sr-ferrites via ball-milling assisted ceramic process and their magnetic properties

M-type hexagonal SrCoxFe12−xO19 (x = 0, 0.1, 0.2, and 0.3) have been synthesized by the ball-milling assisted ceramic process. The influence of Co substitutions on the crystalline structure, lattice strain, morphology, and magnetic behaviors has been investigated. The results show that a high-crystallized hexagonal SrCoxFe12−xO19 is obtained when the precursor is calcined at 950 °C in air for 3 h. Lattice parameters and grain size of SrCoxFe12−xO19 increase with the increase in substitution content (x). Hysteresis behavior varies with substitution content (x) and calcination temperature. M-type hexagonal SrCoxFe12−xO19 (x = 0, 0.1, and 0.2), calcined at 950 °C, with uniaxial anisotropy exhibits a broad M–H loop and rectangular shape. At higher calcination temperature (1050 and 1200 °C) or substitution content (x) is equal to 0.3, the character of the hysteresis loop of SrCoxFe12−xO19 changes from hard into semi-hard. The trend of specific saturation magnetization of SrCoxFe12−xO19, calcined at 950 °C, increases with the decrease in lattice strains. SrFe12O19, calcined at 950 °C, has the highest specific saturation magnetization value (91.30 emu/g) and magnetic moment (17.36 µ B). With the increase of calcination temperature, magnetic domain type of ferrites changes from a single magnetic domain to a multi-domain type.

Effects of Ce[sbnd]Zn co-substitution on structure, magnetic and microwave absorption properties of nickel ferrite nanoparticles

The novel Ce3+ and Zn2+ doped nickel ferrites Ni1−xCexFe2−xZnxO4 (x = 0, 0.05, 0.10, 0.15, 0.20) were prepared by sol-gel auto-combustion method. The structures and morphologies were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). All the XRD patterns showed the single phase of the spinel-type ferrite without other impurity when x ≤ 0.10, and the average crystallite size was about 34.2–53.1 nm. The lattice parameters became larger with the increasing substitution content. The other structure properties such as cation distribution, theoretical ionic radius of a tetrahedral site (rA) and an octahedral site (rB), theoretical lattice parameter (ath), O2− positional parameter (u), cation-cation and cation-anion distances and bond angles were also investigated. The result of FT-IR indicated that Ce3+ substituted Ni2+ in B sites and Zn2+ replaced Fe3+ in A sites. The Ms of substituted ferrites increased with the increase of substitution content when x ≤ 0.10. It was observed that substituted ferrites showed more excellent performance than pure nickel ferrite. The Ni0.9Ce0.1Fe1.9Zn0.1O4 had the best microwave absorption properties. The frequency (with respect to −10 dB) started from 11.56 GHz, and the bandwidth reached about 6.44 GHz. The peak value of RL reached about −21.44 dB at a frequency of 15.52 GHz with a coating thickness of 2.5 mm. The analysis of microwave absorption mechanism indicated that the microwave absorption properties were mainly depended on the input impedance matching, the electromagnetic loss properties and the coating thickness.

Real and Imaginary Parts of Magnetic Susceptibility of Fine Dispersed Nanoparticles Synthesized by Reverse Micelle: From Superparamagnetic Trend to Ferrimagnetic State

Ni0.6Zn0.4Fe2−xCrxO4 (x = 0–0.5) ferrite nanoparticles were prepared using reverse micelle process. X-ray diffraction patterns demonstrated that single phase of spinel ferrites are obtained. TEM micrographs demonstrate the formation of well dispersed nanoparticle with almost spherical morphologies. The EDS analysis proved that the chemical composition has almost uniform distribution in the whole series of samples. Magnetic dynamics of the samples was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Neel–Brown and Vogel–Fulcher models were employed to distinguish between the interacting or non-interacting system. Results exhibited that there is strong interaction between fine particles. The results obtained from vibrating sample magnetometer confirmed that with an increase in chromium content, the saturation magnetization increases. SQUID results at 2 K displayed the ferromagnetic state in nanoparticle and it was found that with an increase in substitution contents, the coercivity decreased.

Determining of Crystallography Site Occupancy and Magnetic Consequences of Substituted Barium Ferrite Nanoparticles Synthesized by Sol-gel Process

BaFe12−xTbx/4Tmx/4Tix/2O19 (x = 0−2.5 in a step of 0.5) substituted barium ferrite nanoparticles were synthesized by a sol-gel method. The structural characteristics of ferrite were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, FTIR, and57Fe Mossbauer spectroscopic measurements. It was found that single-phase barium ferrite nanoparticles with a narrow size distribution were successfully fabricated. The substituted cations were occupied in 12k sites. Vibrating sample magnetometer (VSM) results reflect that with an increase in substitution contents, the coercivity increases, while saturation of magnetization decrease. The reflection loss measurements were carried out on substituted ferrite nanoparticles. The obtained results revealed that the incorporation of Tm–Tb–Ti cations could enhance reflection loss and bandwidth in 8–12 GHz band. The role of matching thickness on the shifts of frequency was also investigated.

Compositional dependence of magnetization reversal mechanism, magnetic interaction and Curie temperature of Co1−xSrxFe2O4 spinel thin film

Co1−xSrxFe2O4, (x varies from 0 to 0.5 in a step of 0.1) nanoparticles were formed by means of sol–gel processing method. The morphological and structural features of nanoparticles were evaluated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FE-SEM) equipped by EDS analysis, Mössbauer spectroscopy and vibrating sample magnetometer. It was found that almost narrow size distribution of nanoparticles with cation distribution occupancy preference in octahedral site was synthesized. The nanoparticles were used for addition in subsequent solution for fabricating ferrite thin films with similar mentioned chemical composition. Several techniques including FE-SEM, atomic force microscopy and vibrating sample magnetometer were employed to find the role of strontium cation distribution on the structural and magnetic properties of films. The Curie temperature, coercivity and magnetic interaction which was evaluated by Henkel plot were reduced by an increase in substitution contents. Coercivity of thin films reduced from 0.65MA/m to 0.39MA/m and Curie temperature declined from 690 to 455°C. The value of strength of interaction was enhanced from −0.23 for x=0 to −0.75 for x=0.5. Angular dependence of coercivity proved that the magnetization reversal process was accompanied by the combination of domain wall motion and Stoner–Wohlfarth rotation, however for thin film with x=0.2–0.5, the reversal mechanism obey the Stoner–Wohlfarth rule.

Tuning static and high frequency magnetic properties of SrFe 12−x (Mn 0.5 Co 0.5 Ti) x/2 O 19 nanoparticles and thin films via chemical control

Abstract This study is intended to evaluate the structural, magnetic, and reflection loss of Mn–Co–Ti susbtituted strontium hexaferrite SrFe 12− x (Mn 0.5 Co 0.5 Ti) x /2 O 19 nanoparticles with x =0–2.5 synthesized by a sol–gel combustion method. The thin films of ferrite with the same composition were also prepared. These particles were evaluated to characterize the structural, magnetic, and reflection loss properties of prepared samples by use of X-ray diffraction, field-emission scanning electron microscopy, Mossbauer spectroscopy, vibrating-sample magnetometer, and vector network analyzer. The XRD and SEM results confirmed the presence of strontium ferrite phase with magnetoplumbite structure and narrow size distribution in all synthesized samples. The substituted cations were located in 4 f 1 and 2 b sites. According to hysteresis loops, magnetization increased and coercivity decreased. The reflection loss characteristics of this ferrite were investigated in the12–18 GHz range. SEM and AFM micrographs showed that with an increase in substitution content, the grain size increases. Magnetic susceptibility of thin films was characterized and it was found that the real parts of susceptibility were decreased by an increase in substitution content, while imaginary parts enhanced.

Development of uniaxial magnetocrystalline anisotropy in SrFe12−x(DyGd)xO19 thin film synthesized by incorporation of high coercivity nanoparticles in sol–gel method

SrFe12−x(DyGd)xO19 thin films with x=0–2.5 were synthesized by a sol–gel method on thermally oxidized silicon wafer (Si/SiO2). XRD patterns and FE-SEM micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. It was found that the grain size is decreased from about 110nm (for the film with no substitution) to 35nm (for the film with the highest amount of substitution cations). AFM micrographs exhibited that the surface roughness decreases with an increase in substitution content. It was found from the VSM graphs that with an increase in substitution contents coercivity and saturation of magnetization increase. The maximum saturation of magnetization and coercivity at perpendicular direction were 250emu/g and 5.5kOe, respectively.

Magnetic and Reflection Loss Characteristics of SrFe$_{12 - {\rm x}}$(Sm$_{0.5}$Dy$_{0.5}$)$_{{\rm x}}$O$_{19}$/Multiwalled Carbon Nanotube Nanocomposite

Samarium-Dysprosium substituted strontium ferrite nanoparticles with composition of SrFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12-x</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x/2</sub> Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x/2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> (x = 0-2.5 in a step of x = 0.5) were synthesized and then deposited on the outer surface of multiwalled carbon nanotubes (MWCNTs) by a sol-gel method. The volume percentage of carbon nanotubes in nanocomposites was 10%. The structural characteristics of ferrite-MWCNTs were studied by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that almost single phase strontium ferrite nanoparticles with narrow size distribution were successfully deposited on MWCNTs. Magnetic susceptibility measurement confirmed that the dynamic magnetic behaviour of samples was described by a Vogel-Fulcher law. SQUID results reflect that with an increase in substitution contents the coercivity and saturation of magnetization decrease. The reflection loss measurements were carried out on substituted ferrite nanoparticles with and without addition of MWCNTs. The obtained results revealed that the incorporation of MWCNTs can enhance reflection loss and bandwidth in Ku band.

Correlation between site preference and magnetic characteristics of self assembled strontium ferrite dot array on functionalized multi-walled carbon nanotubes

In this research work, ferrite nanoparticles with composition of SrFe12−x(Ni0.5Co0.5Ti)x/2O19 (x = 0-2.5 in a step of 0.5) were synthesized by a reverse micelle. Multiwalled carbon nanotubes (MWCNT) were also functionalized by employing poly(acrylic acid). Then the ferrite nanoparticles were deposited on the functionalized surface of carbon nanotubes by hetero-coagulation process. The volume percentage of carbon nanotubes was kept constant at 8 vol. % for synthesizing nanocomposites. The site preference of substituted cations in ferrite crystal structure was determined by 57Fe Mössbauer spectroscopy. It was proved that the substituted cations were distributed in 12 k crystallographic sites. The morphology of ferrite dot array on carbon nanotubes was studied by field emission scanning electron microscopy (FESEM). Quantum Device MPMS-5S SQUID magnetometer was used to probe the variation of magnetization with applied magnetic field. It was found that with an increase in substitution content, the saturation of magnetization and coercivity decrease.

The role of multi-walled carbon nanotubes on the magnetic and reflection loss characteristics of substituted strontium ferrite nanoparticles

Substituted strontium ferrite SrFe12−x(Ni0.5Mn0.5Zr)x/2O19/multi-walled carbon nanotubes (MWCNTs) composites were prepared by a sol–gel method. X-ray diffraction patterns confirm the formation of single phase ferrite nanoparticle and nanocomposites of ferrite/carbon nanotubes. Fourier transform infrared spectroscopy demonstrates the existence of functional groups on the surface of carbon nanotubes. Superconducting quantum interference device measurements showed that the values of specific saturation magnetization increases, while coercivity decreases with an increase in substitution content. Zero field cooled magnetization and field cooled magnetization curves display that with an increase in substitution content, the blocking temperature increases. Field emission scanning electron microscopy micrographs demonstrate that ferrite nanoparticles were attached on external surfaces of the carbon nanotubes. The investigation of the microwave absorption indicates that with an addition of carbon nanotubes, the real and imaginary parts of permittivity and reflection loss enhanced. It is found that with increasing the thickness of absorbers, the resonance frequencies shift to lower regime.

Magnetic properties of substituted strontium ferrite nanoparticles and thin films

SrFe12−x(Zr0.5Mg0.5)xO19 nanoparticles and thin films with x=0–2.5 were synthesized by a sol-gel method on thermally oxidized silicon wafer (Si/SiO2). Structural and magnetic characteristics of synthesized samples were studied employing x-rays diffraction (XRD), transmission electron microscopy (TEM), magnetic susceptometer, atomic force microscopy (AFM), field emission scanning electron microscopy (FE–SEM), and vibrating sample magnetometer (VSM). TEM micrographs display that the narrow size distribution of ferrite nanoparticles with average particle size of 50nm were fabricated. Fitting obtained data of effective magnetic susceptibility by Vogel-Fulcher law confirms the existence of strong magnetic interaction among fine particles. XRD patterns and FE-SEM micrographs demonstrated that single phase c-axis hexagonal ferrite films with rather narrow grain size distribution were obtained. AFM micrographs exhibited that the surface roughness increases with an increase in Zr-Mg content. It was found from the VSM graphs that with an increase in substitution contents the coercivity decreases, while the saturation of magnetization increases. The Henkle plots confirms the existence of exchange coupling among nano-grain in ferrite thin films.

First Study on the Formation of Strontium Ferrite Thin Films on Functionalized Multi-Walled Carbon Nanotube

Substituted strontium ferrite (SrFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12-x</sub> (Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> ) thin films were formed along the surface of multiwalled carbon nanotubes (MWCNTs). Mössbauer spectroscopy indicates that the substituted cations preferentially occupy the 12 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> sites. X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), and vector network analyzer were used to analyze the structure, static, and high-frequency magnetic properties of the prepared samples. It was found that with an increase in substitution content, the saturation of magnetization decreases while the coercivity increases. The CNTs could enhance the real and imaginary parts of permittivity of ferrites. With an increase in volume percentage of MWCNTs, the reflection loss values were increased.