Fine-grained BaTiO3–MgFe2O4 composites prepared by a Pechini-like process

Mapping Intimacies ◽

10.31219/osf.io/ec4fg ◽

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

Download Full-text

BaGeO3 as sintering additive for BaTiO3-MgFe2O4 composite ceramics

10.31219/osf.io/rx9z3 ◽

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.

Download Full-text

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

10.31219/osf.io/zrn2m ◽

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.

Download Full-text

Anomalous and anisotropic nonlinear susceptibility in the proximate Kitaev magnet α-RuCl3

npj Quantum Materials ◽

10.1038/s41535-021-00364-z ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Ludwig Holleis ◽

Joseph C. Prestigiacomo ◽

Zhijie Fan ◽

Satoshi Nishimoto ◽

Michael Osofsky ◽

...

Keyword(s):

Low Temperatures ◽

High Field ◽

Magnetic Order ◽

Exact Diagonalization ◽

Nonlinear Susceptibility ◽

Magnetic Response ◽

Leading Order ◽

Rapid Rise ◽

Quadratic Response ◽

Antiferromagnetic Behavior

AbstractThe leading order nonlinear (NL) susceptibility, χ3, in a paramagnet is negative and diverges as T → 0. This divergence is destroyed when spins correlate and the NL response provides unique insights into magnetic order. Dimensionality, exchange interaction, and preponderance of quantum effects all imprint their signatures in the NL magnetic response. Here, we study the NL susceptibilities in the proximate Kitaev magnet α-RuCl3, which differs from the expected antiferromagnetic behavior. For T < Tc = 7.5 K and field B in the ab-plane, we obtain contrasting NL responses in low (<2 T) and high field regions. For low fields, the NL behavior is dominated by a quadratic response (positive χ2), which shows a rapid rise below Tc. This large χ2 > 0 implies a broken sublattice symmetry of magnetic order at low temperatures. Classical Monte Carlo (CMC) simulations in the standard K − H − Γ model secure such a quadratic B dependence of M, only for T ≈ Tc with χ2 being zero as T → 0. It is also zero for all temperatures in exact diagonalization calculations. On the other hand, we find an exclusive cubic term (χ3) that describes the high field NL behavior well. χ3 is large and positive both below and above Tc crossing zero only for T > 50 K. In contrast, for B ∥ c-axis, no separate low/high field behaviors are measured and only a much smaller χ3 is apparent.

Download Full-text

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

Materials ◽

10.3390/ma11081323 ◽

2018 ◽

Vol 11 (8) ◽

pp. 1323 ◽

Cited By ~ 1

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.

Download Full-text

A new form of Cd3TeO6 revealing dimorphism

Acta Crystallographica Section E Crystallographic Communications ◽

10.1107/s2056989018014214 ◽

2018 ◽

Vol 74 (11) ◽

pp. 1561-1564 ◽

Cited By ~ 2

Author(s):

Matthias Weil ◽

Théo Veyer

Keyword(s):

Phase Formation ◽

Low Temperatures ◽

Structure Type ◽

Site Symmetry ◽

New Form

Phase-formation studies in the system CdO–TeO3 using a CsCl/NaCl melt at comparatively low temperatures revealed that tricadmium orthotellurate(VI), Cd3TeO6, is dimorphic. The new modification of Cd3TeO6 is denoted as the β-form and adopts the rhombohedral Mg3TeO6 structure type with one Cd and two O sites in general positions, and two Te sites with site symmetry \overline{3} each. In comparison with the previously reported monoclinic cryolite-type α-form that was prepared at higher temperatures, β-Cd3TeO6 has a much lower density and most likely represents a metastable modification. Whereas the [TeO6] octahedra in both polymorphs are very similar and show only minor deviations from ideal values, the polyhedra around the CdII sites are different, with a distorted [CdO6] octahedron in both modifications but an additional [CdO8] polyhedron with a [4 + 4] coordination in the α-form.

Download Full-text

Sintering of a fine-grained BaCeO3 powder obtained from a co-precipitation method

10.31219/osf.io/zykmx ◽

2018 ◽

Author(s):

Roberto Köferstein

Keyword(s):

Precursor Powder ◽

Coarse Grained ◽

Precipitation Method ◽

Fine Grained ◽

Grain Sizes ◽

Three Phase ◽

Sintering Behaviour ◽

Co Precipitation ◽

Precursor Powders ◽

Powder Compacts

The formation of BaCeO3 by a co-precipitation method is described herein. The coprecipitationroute leads to an orange (BaCe)-precursor powder (1). To improve the sinteringbehaviour, a small amount of Ge4+ was incorporated, leading to a (BaCe0.95/Ge0.05)-precursor(2). Both precursor powders results in fine-grained preceramic powders (1A, 2A) aftercalcination. The shrinkage and sintering behaviour of resulting powder compacts were studiedin comparison to a coarse-grained mixed-oxide BaCeO3 powder (3). Compacts of 2A reach arelative density of 90 % after sintering at 1350 °C with grain-sizes between 0.9−3.2 μm. Onthe other hand ceramics of 1A and 3 have, after sintering at 1500 °C (10 h), relative densitiesof 85 % and 76 %, respectively. Ceramic bodies of 1A consisted of phase-pure orthorhombicBaCeO3, whereas bodies of 2A show reflections of BaCeO3 and a Ba2GeO4 phase. DTAinvestigations of samples 1A and 2A reveal three phase transitions at 255 °C (1A) and 256 °C (2A) as well as 383 °C (1A) and 380 °C (2A). A very weak one can be obtained in the range880−910 °C

Download Full-text

Use of Fine-Grained Heat-Strengthened Steels to Increase the Operation Qualities of Bunker Capacities from Thin-Walled Galvanized Profiles

Science and Transport Progress Bulletin of Dnipropetrovsk National University of Railway Transport ◽

10.15802/stp2021/227198 ◽

2021 ◽

pp. 84-93

Author(s):

Y. I. Hezentsvei ◽

D. O. Bannikov

Keyword(s):

Low Temperatures ◽

High Strength Steels ◽

High Strength ◽

Numerical Calculations ◽

Structural Scheme ◽

Plan View ◽

Fine Grained ◽

Steel Sheets ◽

Stiffening Ribs ◽

Corrugated Sheets

Purpose. The work is aimed to study the use efficiency of fine-grained heat-strengthened steels (mainly 10G2FB) for steel bunker capacities. At the same time, the structural scheme of such a structure using corrugated steel sheets is considered as the main variant. Methodology. To achieve this purpose, a series of numerical calculations was carried out for a steel bunker capacity of a pyramidal-prismatic type with overall dimensions in plan view of 6×5.2 m and a total height of 4.5 m. The capacity was designed for complicated working conditions, in particular, increased loads, including long-term dynamic ones. The potential possibility of operating the container under conditions of high or low temperatures was also taken into account. At the same time, both the traditional structural scheme of a bunker capacity with horizontal stiffening ribs and the developed structural scheme based on corrugated steel sheets were analyzed. The calculations were carried out by the finite element method based on the SCAD for Windows project complex. Findings. Based on the results of the analysis and comparison of the data obtained in numerical calculations, it was found that the use of fine-grained heat-strengthened high-strength steels (for example, steel 10G2FB) for bunker capacities, both the traditional structural scheme with stiffening ribs and the developed structural scheme based on corrugated sheets, allows reducing material consumption by about 30% in both cases. At the same time, due to the good performance of fine-grained heat-strengthened steel 10G2FB, both at high and at low temperatures, it can be effectively used for steel bunker capacities that work in difficult conditions. Originality. The possibility and efficiency of the use of fine-grained, heat-strengthened high-strength steels for the construction of a steel bunker capacity is estimated. At the same time, such an estimation was given not only for structures of the traditional structural scheme with horizontal stiffening ribs, but also for bunkers with a developed structural scheme based on corrugated sheets. Practical value. From a practical point of view, quantitative parameters of the stress-strain state were obtained during investigations of various design variants for a steel bunker capacity. The data are presented in a compact form that is easy to evaluate and compare. They allow us to state about the improvement of the operation characteristics of capacities and the potential reduction of the risks of their failures and accidents during operation.

Download Full-text

Microstructure features of the BST/(Mg, Ln)-ceramic

Journal of Advanced Dielectrics ◽

10.1142/s2010135x21600055 ◽

2021 ◽

pp. 2160005

Author(s):

K. P. Andryushin ◽

A. V. Nagaenko ◽

S. V. Khasbulatov ◽

L. A. Shilkina ◽

E. V. Glazunova ◽

...

Keyword(s):

Solid Solutions ◽

Solid Phase Synthesis ◽

Solid Phase ◽

Functional Materials ◽

Ceramic Technology ◽

Phase Synthesis ◽

Fine Grained ◽

Average Grain Size ◽

Crystallite Sizes ◽

Fine Grained Structure

Solid solutions of the composition Ba[Formula: see text](Mg, Ln)[Formula: see text]Sr[Formula: see text]TiO3 ([Formula: see text] = 0.01; 0.025; 0.04; [Formula: see text] = 0.20; 0.50; 0.80; Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb) were prepared by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. The influence of rare-earth elements on the microstructure of the prepared ceramic samples was investigated. It was found that regardless of the type of modifiers introduced, the grain landscape of the studied solid solutions with different amounts of SrTiO3 is refined (in the initial system, the average grain size, [Formula: see text], at [Formula: see text] = 0.20 is 6 [Formula: see text]m; at [Formula: see text] = 0.50 is 4 [Formula: see text]m; at [Formula: see text] = 0.80 is 18 [Formula: see text]m) to crystallite sizes not exceeding (2–3) [Formula: see text]m, and compacted. The using of mechanical activation procedures leads to an even greater decrease in the size and an increase in the density of ceramics. The increasing in the concentration of modifiers in each group (within the considered range of dopant variation) against the background of such a fine-grained structure has little effect on the dynamics of changes in [Formula: see text]. It is concluded that it is advisable to use the data obtained in the development of functional materials based on BST/(Mg, Ln) and devices with the participation of these compositions.

Download Full-text