Traditional Ceramic Route Research Articles

Sintered microstructure effect on RF-wave shielding properties of a Cu-doped Ni–Zn-polycrystalline ferrite

The shielding properties of a Cu-doped Ni–Zn polycrystalline ferrite in the frequency range 1MHz to 1GHz were explored. Samples of composition (Cu0.12Ni0.23Zn0.65)Fe2O4 were prepared by the traditional ceramic route. The complex relative permittivity (εr=ε′−jε″) and permeability (μr=μ′−jμ″) of the absorber ceramics were measured, and the minimum reflection-loss RL, matching frequency fm, matching thickness dm and bandwidth for RL≤−20 dB were calculated using the theory of the absorbing wall. Effect of the main process parameters (pressing pressure P, sintering temperature T, and sintering time t) on the electromagnetic properties and microwave-absorbing characteristics was deeply investigated. The rise of the three selected process parameters was observed to improve the sintered microstructure of the final specimens (monitored by the relative density ϕ and the average grain size G), provided that abnormal grain growth does not occurred. The increase in sintered relative density and average grain growth modifies complex permeability and permittivity in the explored frequency range, enhancing the shielding properties of the material.

Ferromagnetic resonance induced large microwave magnetodielectric effect in cerium doped Y3Fe5O12 ferrites.

In recent years, multifunctional materials contained simultaneous ferroelectric and ferromagnetic ordering have been realized. Here, a real time room temperature adaptive materials system, which demonstrates an RF magnetodielectric (MD) response, i.e., CexY3−xFe5O12 (x = 0, 0.05, 0.1, 0.15, 0.2), is reported. The magnetic and dielectric properties of Ce-doped YIG microwave ferrites processed by a traditional ceramic route have been measured over a frequency range of 4–8 GHz (C-band). The substitution of Ce not only enhances the microwave electromagnetic properties of the YIG, but also modulates the magnetodielectric response. The maximum magnetodielectric response in Ce-doped YIG sample ranges in magnitude from approximately +5% to −5% under an applied field of 1.78 kOe. This effect was attributed to electron fluctuations on the Fe cation sites. Furthermore, the magnitude of the MD response was shown to be enhanced by the cerium content. It is believed that research of the magnetodielectric effect in YIG ferrites is of great importance to the development of next generation multifunctional adaptive microwave materials, devices and integrated circuits.

Structural and magnetic characteristics of La–Zn doped M-type Sr–Ca hexaferrites with different iron content

In this work, La–Zn doped M-type Sr–Ca hexaferrites Sr0.41Ca0.30La0.29FexZn0.25O19 (x=10.00–10.75) have been prepared by the traditional ceramic route. The phase composition of the magnetic powders was examined by X-ray diffraction. It was found that the magnetic powders with Fe content (10.00≤x≤11.50) consists of only one phase and the hematite (α-Fe2O3) phase is observed in the magnetic powder with Fe content (x) of 11.75. The surface morphology and magnetic properties of the sintered magnets were characterized by a field emission scanning electron microscopy and a magnetic properties test instrument. SEM images of the sintered magnets showed the hexagonal platelet shape. With increasing the Fe content (x), the remanence and maximum energy product were first increased and reached to a maximum and then decreased. While the intrinsic coercivity and magnetic induction coercivity increased with Fe content (x) from 10.00 to 11.75.

In situ formation of coloured M(II)–doped Zn2SiO4–willemite in ceramic glazes (M=Mn, Co, Ni, Cu)

The family of M(II) substituted ZnO–wurtzite was investigated as potential new ceramic pigments. When MxZn1−xO or (MM׳)xZn1−xO with (M/M′=Mn, Co, Ni, Cu) oxides are incorporated to industrial frits the development of new colour hues is observed. This is attributed to the in situ formation of coloured M(II)–doped Zn2SiO4–willemite in ceramic glazes. The pigments were prepared by solid state reaction through the traditional ceramic route. Prior to enamelling, the materials were characterized by XRD analysis and FTIR spectroscopy. The colour performance and technological properties of the enamels were evaluated by enamelling in batches containing 5wt% with a transparent frit, representative of single firing industrial procedures, and submitting them to thermal treatment at 1000°C. The colours obtained, once the glazes were formed are attributed mainly to the formation of crystalline Zn2SiO4 within the glassy matrix, when chromophore M(II) ions enter into the tetrahedral coordination Zn(II) site available in willemite. The colorimetric CIELab parameters measured are in good agreement with the structural and spectroscopic analyses. The colour of some glassy coatings was interpreted by analysing the reflectance UV–visible electronic spectra of the samples. This study demonstrates that this family of pigment is capable of forming its own Zn-based crystals in a conventional transparent ceramic frit giving rise to a wide palette of colours. When Mn, Co, Ni and Cu are present in the Zn(II) site light brown, deep blue, pale yellow and green, are achieved respectively. Furthermore the simultaneous doping with a combination of MM′ results in various nice new shades of colours, enlarging the palette of green, yellow, brown and blue hues. The homogeneity of the enamels was confirmed by SEM–EDX microscopy. These materials are promising for ceramic applications since a low amount of pigment would be necessary to achieve intense colouration.

Synthesis of Ceramic Pigments ACr<sub>2</sub>O<sub>4</sub> Using the Non-Conventional Method of Co-Precipitation Assisted by Ultrasound and High Energy Milling

In this research ceramic pigments have been synthesized with crystalline spinel structure and chromium based with a stoichiometry ACr2O4. A was an element with +2 valence metal, in this case, metals were zinc and iron, these pigments have been synthesized by non-conventional methods like the co-precipitation assisted by ultrasound and high milling energy. Pigments were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrophotometry, and colorimetric CIELab method. Results showed that it was possible to obtain a crystallin desired structure at temperatures below 900&#176C by non-conventional methods. These results showed the advantages of ceramic pigments obtained by alternative routes, because it was possible to have a better control over stoichiometry and colorimetric structure properties. Furthermore, they were obtained at temperatures lower than those used by the traditional ceramic route.

Foamlike Porous Spinel MnxCo3−xO4 Material Derived from Mn3[Co(CN)6]2⋅nH2O Nanocubes: A Highly Efficient Anode Material for Lithium Batteries

A new facile strategy has been designed to fabricate spinel Mn(x)Co(3-x)O(4) porous nanocubes, which involves a morphology-conserved and pyrolysis-induced transformation of Prussian Blue Analogue Mn(3)[Co(CN)(6)](2)⋅nH(2)O perfect nanocubes. Owing to the release of CO(2) and N(x)O(y) in the process of interdiffusion, this strategy can overcome to a large extent the disadvantage of the traditional ceramic route for synthesis of spinels, and Mn(x)Co(3-x)O(4) with foamlike porous nanostructure is effectively obtained. Importantly, when evaluated as an electrode material for lithium-ion batteries, the foamlike Mn(x)Co(3-x)O(4) porous nanocubes display high specific discharge capacity and excellent rate capability. The improved electrochemical performance is attributed to the beneficial features of the particular foamlike porous nanostructure and large surface area, which reduce the diffusion length for Li(+) ions and enhance the structural integrity with sufficient void space for buffering the volume variation during the Li(+) insertion/extraction.

Efeito da variação estequiométrica na formação de ferritas BaM produzidas pelo método SHS e pelo método cerâmico tradicional

As ferritas do tipo BaM são cerâmicas ferrimagnéticas, usualmente aplicadas em sistemas de gravação magnética e como magnetos duros. Possuem alta estabilidade química, resistência a corrosão e baixo custo de produção. Diante da sua crescente importância, foi estudado o efeito da contribuição do excesso de bário no processamento e formação da fase ferrita BaM por duas distintas rotas: processamento por mistura de óxidos e a síntese por reação de combustão (método SHS) com o uso de carbonato e nitrato de bário. Duas relações de concentração entre bário e ferro foram utilizadas, uma estequiométrica (n = Fe2O3/BaO = 6) e uma outra não estequiométrica (n = Fe2O3/BaO = 5,45). Os pós processados com excesso de bário resultaram na presença da fase intermediária de formação BaFe2O4, a qual permanece após altas temperaturas de calcinação e mesmo após a sinterização de compactos obtidos a partir dos pós calcinados. As conclusões foram baseadas em difratogramas de raios X das ferritas BaM em pó após calcinação e nas amostras conformadas e sinterizadas, além de imagens obtidas por microscopia eletrônica de varredura. Os resultados de medidas magnéticas indicam a diminuição da coercividade, da indução magnética remanente e dos valores de BH Máx dos pós obtidos com a contribuição do excesso de bário, provavelmente devido à presença da fase intermediária não magnética. Este efeito negativo foi mais efetivo nos pós processados pelo método SHS, chegando a uma redução de 28,8% no valor de coercividade e 35,1% no valor de BH Máx. Os pós de ferritas BaM obtidos pelo método cerâmico tradicional apresentaram maiores valores de coercividade (4,28 kOe) e BH Máx (0,87 MOe*emu/g) e a influência do excesso de bário na formulação foi menos prejudicial sobre suas propriedades magnéticas.

The optimum synthesis of high coercivity Pb–M hexaferrite powders using modifications to the traditional ceramic route

PbFe12O19 hexaferrite powders with high coercivities were obtained using modifications to the traditional ceramic route. Mössbauer and X-ray diffraction measurements indicates that the M-type hexagonal phase coexist with the α-Fe2O3 phase at the temperature range of 800<T<900°C and the homogeneous state is reached at 900°C. The optimum values of saturation magnetization and coercive field at this temperature were 62.00 emu/g and 4.0 kOe, respectively. At T>900°C, the magnetic properties are drastically affected as a consequence of the volatility of PbO.

Synthesis of Ferroelectric Bi4Ti3O12 by Alternative Routes: Wet No-Coprecipitation Chemistry and Mechanochemical Activation

Novel synthesis methods have been investigated for the preparation of Bi4Ti3O12 ferroelectric Aurivillius-type powders, namely, the wet no-coprecipitated chemistry using a n-butylamine aqueous solution and two mechanochemical activation techniques (vibrating and planetarium mills). For the sake of comparison, Bi4Ti3O12 powders were also produced by the traditional ceramic route. The syntheses of the crystalline phases were obtained by annealing of the precursors at different temperatures and times. Both the precursors and the thermally treated products were characterized by means of X-ray powder diffraction, thermal analysis, and scanning electron microscopy. The Aurivillius phase was found to appear at 600 °C for vibrating and 500 °C for planetarium-milled precursors. These temperatures are 250−350 °C lower than those reported for the traditional ceramic route (850 °C). Moreover, the stabilization at room temperature of a new fluorite Bi−Ti−O structure was obtained by use of the planetarium milling precu...

Synthesis and electrical conductivity of Y1−xMn1−yO3−δ

Abstract YMnO3-related materials [stoichiometric (Y/Mn =1), and Y or Mn deficient] were synthesized by a traditional ceramic route. Dense pellets obtained after sintering at different temperatures (1400–1500°C) were characterized by XRD, SEM/EDS, dilatometry (up to 1270°C) and dc electrical conductivity measurements in air (between 200 and 1000°C). The electrical conductivities of all compositions were close to each other and within the range 10−4 S/cm at about 200°C to 1 S/cm at about 1000°C. Arrhenius plots show three different slopes with smooth transitions around 300–350°C and 600–650°C. The activation energy increases from about 50 kJ/mol below 300°C to about 90 kJ/mol between 650 and 1000°C. XRD, SEM/EDS and thermal expansion measurements provided enough evidence on phase and mechanical stability constraints, thus questioning potential technological applications.

Zr4+and Ti4+substitution in gallium garnets

A study was undertaken of the formation of solid solutions with the garnet structure in the systems M3Ga5O12–M′O2–CaO (where M = Y3+, Nd3+ and M′= Zr4+, Ti4+). Synthesis of these compounds was performed by the traditional ceramic route as well as through hydroxide coprecipitation. Characterization was mainly carried out by X-ray diffraction, applying automatic structure-refining techniques. The Zr4+ and Ti4+ cations were shown to substitute for Ga3+ in octahedral sites, although there might be a degree of tetrahedral site distribution in the case of Ti4+, and the formation limits of the solid solutions for the systems were established. The application of concepts such as ionic size and charge was seen to be fundamental for understanding the behaviour of these garnets.