scholarly journals Magnetic, optical, dielectric, and sintering properties of nano-crystalline BaFe0.5Nb0.5O3 synthesized by a polymerization method

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Crystallite Size ◽  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Secondary Phase ◽  
Phase Evolution ◽  
One Pot ◽  
Nano Crystalline ◽  
Rc Circuit ◽  
Tan Δ ◽  
Polymerization Method

Full text also available at: http://rdcu.be/v7Fn A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 μm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Neel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 9 104 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit.

scholarly journals BaGeO3 as sintering additive for BaTiO3-MgFe2O4 composite ceramics

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Magnetic Measurements ◽  
Sol Gel ◽  
Dissipation Factor ◽  
Composite Ceramics ◽  
Composite Powders ◽  
One Pot ◽  
Fine Grained ◽  
Sintering Additive ◽  
Nano Crystalline ◽  
Sintering Behaviour

BaTiO3-MgFe2O4 composites (30 wt.% MgFe2O4) with a small addition of BaGeO3 as a sintering additive were synthesized by a one-pot Pechini-like sol-gel process. Nano-crystalline composite powders with a crystallite size of about 10 nm were obtained after reaction at 700 °C for 1 h. Magnetic investigations suggest that the nano-powder is in its superparamagnetic state at room temperature. The addition of BaGeO3 leads to an improved sintering behaviour. DTA measurements reveal the formation of a liquid phase at 1164(3) °C. Dense ceramic bodies (relative density > 90 %) were obtained after sintering for 1 h at 1150 °C. SEM investigations prove a 0-3 connectivity and show that the addition of BaGeO3 promotes the grain growth leading to particles up to 4 μm. In contrast, fine-grained composite ceramics with smaller particles up to 230 nm were obtained after a two-step sintering process. Magnetic measurements indicate a ferrimagnetic behaviour with coercivity values up to 70 Oe depending on the sintering procedure. Furthermore, addition of BaGeO3 results in an increase of the relative permittivity, whereas the dissipation factor slightly decreases.

scholarly journals Fine-grained magnetoelectric Sr0.5Ba0.5Nb2O6–CoFe2O4 composites synthesized by a straightforward one-pot method

2021 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Impedance Spectroscopy ◽  
Magnetic Measurements ◽  
Composite Ceramics ◽  
Composite Powders ◽  
One Pot ◽  
Driving Field ◽  
Fine Grained ◽  
Magnetoelectric Coefficient ◽  
Rc Circuit ◽  
Nanocrystalline Composite

Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistrysynthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. =24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%.SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizesfrom 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in themicrostructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviourwith saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe.Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both withrising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described usinga single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. Themaximum magnetoelectric coefficient (αME) depends both on the CoFe2O4 fraction (x) and sintering temperature.The composite with x = 0.3 exhibits the largest αME value of 37 μV Oe1 cm1 (@ 900 Hz). With rising frequencyof the AC driving field αME increases up to 300–400 Hz and is nearly constant until 1 kHz.

scholarly journals Investigations of nano-crystalline Sr0.5Ba0.5Nb2O6 and bulk ceramics synthesized by a polymerization method using PEG400

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Optical Band Gap ◽  
Linear Thermal Expansion Coefficient ◽  
Sintering Temperature ◽  
Linear Thermal Expansion ◽  
Dielectric Measurements ◽  
One Pot ◽  
Grain Sizes ◽  
Nano Crystalline ◽  
Polymerization Method ◽  
Diffuse Phase

Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr0.5Ba0.5Nb2O6with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g-1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 μm, whereas higher temperatures lead to a rod-like microstructure. Theindirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The melting temperature is determined as 1506(7) °C with dHf = 140(20) kJ mol-1. The average linear thermal expansion coefficient is found to be 10.5(5)^10-6 K-1.

Nano-Crystalline Barium Hexaferrite Powders Prepared by Mechanical Alloying Using Acetate Precursor

2008 ◽  
Vol 368-372 ◽  
pp. 610-612 ◽  
Author(s):  
M. Honarvar Nazari ◽  
Abolghasem Ataie ◽  
S.A. Seyyed Ebrahimi
Keyword(s):  
Heat Treatment ◽  
Magnetic Properties ◽  
Phase Composition ◽  
Mechanical Alloying ◽  
Thermal Behavior ◽  
Crystallite Size ◽  
Barium Hexaferrite ◽  
Subsequent Heat Treatment ◽  
Molar Ratios ◽  
Nano Crystalline

Nano-crystalline barium hexaferrite powders have been prepared by mechanical alloying of nFe2O3+Ba(CH3COO)2 with Fe/Ba molar ratios of 10-12 and subsequent heat treatment. Thermal behavior, phase composition, morphology and magnetic properties of samples were studied using DTA/TGA, XRD, SEM and VSM, respectively. Nano-crystalline Ba-hexaferrite with a mean crystallite size of 46 nm and magnetic properties as high as Ms = 73.9 A.m2/kg and Hci = 334.2 kA/m was formed for mixture of 5.5Fe2O3+Ba(CH3COO)2 which was milled for 48 h and then annealed at 1100 °C.

AN INVESTIGATION INTO MECHANOCHEMICAL SYNTHESIS OF NANOCRYSTALLINE HEXAFERRITE POWDER

2011 ◽  
Vol 25 (07) ◽  
pp. 987-993
Author(s):  
S. SADEGHI-NIARAKI ◽  
S. A. SEYYED EBRAHIMI ◽  
SH. RAYGAN
Keyword(s):  
Crystallite Size ◽  
Single Phase ◽  
Sol Gel ◽  
Milled Powder ◽  
Particle Morphology ◽  
Average Crystallite Size ◽  
Phase Evolution ◽  
High Energy ◽  
Strontium Hexaferrite ◽  
Electron Microscopes

Nanocrystalline strontium hexaferrite powder has been prepared by a new mechanochemical method in which the single phase hexaferrite was obtained via a sol–gel autocombustion process followed by an intermediate high energy milling step and subsequent annealing. The effects of the intermediate milling on the phase evolution, crystallite size and annealing behavior of the final products were investigated using the X-ray diffraction (XRD) technique. The single phase strontium hexaferrite was obtained at an annealing temperature of 800°C, while this temperature was 1,000°C for the powder synthesized without milling. It could be seen that an intermediate milling accelerates the formation of strontium hexaferrite during the calcination process. The results showed that in the milled powder, the average crystallite size of the ferrite was about 40 nm and much smaller than that of the nonmilled powder. Magnetic properties were also measured by a vibrating sample magnetometer (VSM). The particle morphology was then studied by scanning and transmission electron microscopes (SEM and TEM).

scholarly journals One-Step Soft Chemical Synthesis of Magnetite Nanoparticles under Inert Gas Atmosphere. Magnetic Properties and In Vitro Study

Nanomaterials ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1500
Author(s):  
Laura Madalina Cursaru ◽  
Roxana Mioara Piticescu ◽  
Dumitru Valentin Dragut ◽  
Robert Morel ◽  
Caroline Thébault ◽  
...  
Keyword(s):  
Crystallite Size ◽  
Magnetite Nanoparticles ◽  
Biomedical Applications ◽  
Magnetic Measurements ◽  
Magnetic Moments ◽  
Inert Gas ◽  
Size Analysis ◽  
Hydrodynamic Diameter ◽  
Magnetic Cores ◽  
Gas Atmosphere

Iron oxide nanoparticles have received remarkable attention in different applications. For biomedical applications, they need to possess suitable core size, acceptable hydrodynamic diameter, high saturation magnetization, and reduced toxicity. Our aim is to control the synthesis parameters of nanostructured iron oxides in order to obtain magnetite nanoparticles in a single step, in environmentally friendly conditions, under inert gas atmosphere. The physical–chemical, structural, magnetic, and biocompatible properties of magnetite prepared by hydrothermal method in different temperature and pressure conditions have been explored. Magnetite formation has been proved by Fourier-transform infrared spectroscopy and X-ray diffraction characterization. It has been found that crystallite size increases with pressure and temperature increase, while hydrodynamic diameter is influenced by temperature. Magnetic measurements indicated that the magnetic core of particles synthesized at high temperature is larger, in accordance with the crystallite size analysis. Particles synthesized at 100 °C have nearly identical magnetic moments, at 20 × 103 μB, corresponding to magnetic cores of 10–11 nm, while the particles synthesized at 200 °C show slightly higher magnetic moments (25 × 103 μB) and larger magnetic cores (13 nm). Viability test results revealed that the particles show only minor intrinsic toxicity, meaning that these particles could be suited for biomedical applications.

scholarly journals A Facile Method Using a Flux to Improve Quantum Efficiency of Submicron Particle Sized Phosphors for Solid-State Lighting Applications

Ceramics ◽  
2018 ◽  
Vol 1 (1) ◽  
pp. 38-53 ◽  
Author(s):  
Jungmin Ha ◽  
Ekaterina Novitskaya ◽  
Gustavo Hirata ◽  
Chenhui Zhou ◽  
Robyn Ridley ◽  
...  
Keyword(s):  
Crystallite Size ◽  
Quantum Efficiency ◽  
Secondary Phase ◽  
Luminescent Properties ◽  
Lattice Parameters ◽  
The Other ◽  
Solid State Lighting ◽  
Submicron Particle ◽  
Flux Composition ◽  
Judicious Choice

This work successfully verified that the addition of a flux (NH4F, NH4Cl, and H3BO3) during synthesis has an impact on the crystallite size and quantum efficiency of submicron-sized particles of CaMgSi2O6:Eu2+ phosphors. The addition of NH4F or NH4Cl increased the crystallite size in the submicron-sized particles, yielding an increase in emission intensity and quantum efficiency. On the other hand, the use of the H3BO3 flux crystallized a secondary phase, SiO2, and changed the lattice parameters, which degraded the luminescent properties. In addition, an excessive amount of NH4Cl was examined, resulting in nucleation of a secondary phase, CaSiO3, which changed the lattice parameters with no improvement in luminescent properties. These results demonstrate that the addition of a flux could be a method to improve the quantum efficiency of submicron-sized particles composed of nanocrystallites; however, a judicious choice of the flux composition and amount has to be carefully considered.

scholarly journals One-pot preparation of poly(styrene-co-divinylbenzene)/silver nanoparticles composite microspheres with tunable porosity and their catalytic degradation of methylene blue in aqueous solution

RSC Advances ◽  
2017 ◽  
Vol 7 (79) ◽  
pp. 50176-50187 ◽  
Author(s):  
Xiaohuan Ji ◽  
Franziska Griesing ◽  
Ruijia Yan ◽  
Bin Sun ◽  
Werner Pauer ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Methylene Blue ◽  
Silver Nanoparticles ◽  
Silver Nanoparticle ◽  
Catalytic Degradation ◽  
One Pot ◽  
Composite Microspheres ◽  
Polymerization Method ◽  
Porous Poly

Porous poly(styrene-co-divinylbenzene)/silver nanoparticle composite spheres with tunable porosity were synthesized by seed swelling polymerization method and show a great catalytic degradation of methylene blue within NaBH4.

STRUCTURAL, SURFACE MORPHOLOGICAL AND MAGNETIC STUDIES OF Zn1−xFexS (x=0.00–0.10) DILUTED MAGNETIC SEMICONDUCTORS GROWN BY CO-PRECIPITATION METHOD

2018 ◽  
Vol 25 (01) ◽  
pp. 1850044
Author(s):  
M. HASSAN ◽  
M. GHAZANFAR ◽  
N. AROOJ ◽  
S. RIAZ ◽  
S. SAJJAD HUSSAIN ◽  
...  
Keyword(s):  
Crystallite Size ◽  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Hysteresis Loops ◽  
Secondary Phase ◽  
Precipitation Method ◽  
Ferromagnetic Behavior ◽  
Magnetic Studies ◽  
Diluted Magnetic ◽  
Co Precipitation

We have fabricated Zn[Formula: see text]FexS ([Formula: see text], 0.02, 0.04, 0.06, 0.08 and 0.10) diluted magnetic semiconductors using co-precipitation method. X-ray diffraction patterns depict that Zn[Formula: see text]FexS appears as a dominant phase with cubic zinc blende structure and nanoscale crystallite size. In addition, a secondary phase of rhombohedral ZnS also appears; however, no additional phase arises that primarily belongs to Fe dopant. Using Debye–Scherrer relation, the crystallite size is found to be in the range of 20–27[Formula: see text]nm, which is in good agreement with the crystallite size calculated using the Williamson–Hall (WH) plot method. The appearance of secondary phase provoked to study the residual strain using Stokes–Wilson equation, which is nearly consistent to that observed using WH plot method. The surface morphology, revealed using scanning electron microscopy, depicts non-uniform surface structure with a variety of grains and void dimensions. Hysteresis loops measured for Zn[Formula: see text]FexS at room temperature (RT) illustrate a paramagnetic behavior at higher fields; however, small ferromagnetic behavior is evident due to the small openings of the measured hysteresis loops around the origin. The measured RT ferromagnetism reveals the potential spintronic device applications of the studied diluted magnetic semiconductors.

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