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 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 BaTiO3–MgFe2O4 composites prepared by a Pechini-like process

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Phase Formation ◽  
Low Temperatures ◽  
High Field ◽  
Composite Powders ◽  
One Pot ◽  
Fine Grained ◽  
Crystallite Sizes ◽  
Sintering Behaviour

The synthesis of BaTiO3–MgFe2O4 composite powders by a Pechini-like one-pot process and resultingceramic bodies is described herein. Phase formation during the decomposition of homogenous (Ba, Ti,Fe, Mg)-gels was monitored up to 1200 ?C. Composite powders consisting of BaTiO3 and MgFe2O4 wereobtained after decomposition at 700 ?C for 1 h resulting in crystallite sizes of about 10 nm. The shrinkageand sintering behaviour of compacted powders were examined. Sintering at >1200 ?C leads to theformation of hexagonal BaTiO3 only for composites with a MgFe2O4 content of >30 wt.%. SEM imagesof ceramic bodies reveal that the MgFe2O4 particles are surrounded by BaTiO3 crystallites. Magneticmeasurements of both powders and corresponding ceramic bodies show ferrimagnetic behaviour withlow coercivities. At high-field and low temperatures an additional small paramagnetic contributionwas observed which increases with decreasing MgFe2O4 content and should be considered by the calculationof the saturation magnetization.Finally, the

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 Mechanical Milling-Assisted Spark Plasma Sintering of Fine-Grained W-Ni-Mn Alloy

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1323 ◽  
Author(s):  
Yanlin Pan ◽  
Daoping Xiang ◽  
Ning Wang ◽  
Hui Li ◽  
Zhishuai Fan
Keyword(s):  
Spark Plasma Sintering ◽  
Mechanical Milling ◽  
Bending Strength ◽  
Sintering Temperature ◽  
Interface Fracture ◽  
Composite Powders ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Binding Phase ◽  
Spark Plasma

Fine-grained W-6Ni-4Mn alloys were fabricated by spark plasma sintering (SPS) using mechanical milling W, Ni and Mn composite powders. The relative density of W-6Ni-4Mn alloy increases from 71.56% to 99.60% when it is sintered at a low temperature range of 1000–1200 °C for 3 min. The spark plasma sintering process of the alloy can be divided into three stages, which clarify the densification process of powder compacts. As the sintering temperature increases, the average W grain size increases but remains at less than 7 µm and the distribution of the binding phase is uniform. Transmission electron microscopy (TEM) observation reveals that the W-6Ni-4Mn alloy consists of the tungsten phase and the γ-(Ni, Mn, W) binding phase. As the sintering temperature increases, the Rockwell hardness and bending strength of alloys initially increases and then decreases. The optimum comprehensive hardness and bending strength of the alloy are obtained at 1150 °C. The main fracture mode of the alloys is W/W interface fracture.

Fine-grained BNT-based lead-free composite ceramics with high energy-storage density

2019 ◽  
Vol 45 (16) ◽  
pp. 19895-19901 ◽  
Author(s):  
Weigang Ma ◽  
Pengyuan Fan ◽  
David Salamon ◽  
Suwadee Kongparakul ◽  
Chanatip Samart ◽  
...  
Keyword(s):  
Energy Storage ◽  
High Energy ◽  
Lead Free ◽  
Energy Storage Density ◽  
Composite Ceramics ◽  
Storage Density ◽  
Fine Grained ◽  
High Energy Storage Density ◽  
High Energy Storage

Structure Evolution in Al2O3 - ZrO2(Y2O3) Ceramic Composites during Sintering

2010 ◽  
Vol 65 ◽  
pp. 11-15
Author(s):  
Ya. Dyatlova ◽  
S.S. Ordanyan ◽  
Andrey Osmakov ◽  
V. Pesin ◽  
V. Rumyantsev
Keyword(s):  
Mechanical Behavior ◽  
Ceramic Composite ◽  
Large Angle ◽  
Tetragonal Zirconia ◽  
Ceramic Composites ◽  
Structure Evolution ◽  
Composite Ceramics ◽  
X Ray Diffraction ◽  
Composite Powders ◽  
Microstructure Parameters

The paper demonstrates the possibility to control the degree of tetragonal zirconia stabilization, microstructure and physical and mechanical behavior of Al2O3 -ZrO2(Y2O3) ceramic composite. Control is exerted via the process variables during deposition synthesis of nanosized composite powders from hydroxide salts, and their subsequent heat treatment and consolidation. Morphology features of nanosized powder systems and microstructures of the consolidated nanostructured materials were characterized by BET surface are measurements, scanning electron microscopy (both standard and HR), and large-angle X-ray diffraction. Correlations are established between microstructure parameters, physical and mechanical behavior of composite ceramics and a degree of stabilization of tetragonal ZrO2.

Spark Plasma Sintering of fine-grained YAG:Nd+MgO composite ceramics based on garnet-type oxide Y2.5Nd0.5Al5O12 for inert fuel matrices

2019 ◽  
Vol 226 ◽  
pp. 323-330 ◽  
Author(s):  
L.S. Alekseeva ◽  
A.I. Orlova ◽  
A.V. Nokhrin ◽  
M.S. Boldin ◽  
E.A. Lantsev ◽  
...  
Keyword(s):  
Spark Plasma Sintering ◽  
Composite Ceramics ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma

Effect of Sintering Process on Microstructure of Al2O3/LiTaO3 Composite Ceramics

2007 ◽  
Vol 336-338 ◽  
pp. 2363-2365
Author(s):  
You Feng Zhang ◽  
Yu Zhou ◽  
De Chang Jia ◽  
Qing Chang Meng
Keyword(s):  
Grain Boundaries ◽  
Relative Density ◽  
Theoretical Density ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Hot Press ◽  
Composite Ceramics ◽  
Fine Grained ◽  
N2 Atmosphere ◽  
Hot Press Sintering

Effects of different sintering methods such as pressureless sintering and hot press sintering on relative density and microstructure of the Al2O3p/LiTaO3 (ALT) composite ceramics were investigated to obtain a preferable sintering process. Relative densities of all ALT composites are below 90% when sintered with the cold isostatical pressing followed by pressureless sintering at temperatures of 1250 to 1350°C. The relative densities and microstructure of ALT composite ceramics with the hot press sintering process in a N2 atmosphere at 1150 and 1300°C were investigated. The relative density of ALT composite hot pressed at 1150°C is only 77%, and almost theoretical density at 1300°C. This indicates that sintering pressure plays an important role in the densification of ALT composite ceramics in temperature range of 1150 to 1350°C. Investigation on morphologies of the composites shows that the Al2O3 particles distributed along grain boundaries of LiTaO3, which leads to a fine-grained microstructure in the ALT composite ceramics

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