Microwave dielectric properties of (Bi1−xFex)NbO4 ceramics prepared by the sol–gel method

Devesa, Susana; Graça, M.P.F.; Henry, F.; Costa, L.C.

doi:10.1016/j.ceramint.2015.03.038

Cited by 17 publications

(8 citation statements)

References 15 publications

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“…The obtained results are summarized in Table 1 . The average crystallite sizes of lithium ferrite crystal phase determined by the Scherrer method,

, uses the following Debye–Scherrer equation [ 49 ]:

where

is the wavelength of X-ray radiation (1.54184 Å), N is a numerical factor frequently referred to as the crystallite-shape factor [ 49 ], where n = 0.9 is a good approximation for particles with a spherical habit [ 50 ],

is the diffraction angle, and β is the full width half maximum (FWHM) of the diffracted peaks, corrected by the relation

, where

and

are the experimental and the instrumental width. The instrumental width was determined using the LaB 6 powder standard pattern (SRM 660—National Institute of Standard Technology).…”

Section: Resultsmentioning

confidence: 99%

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

et al. 2021

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The physical properties of the cubic and ferrimagnetic spinel ferrite LiFe5O8 has made it an attractive material for electronic and medical applications. In this work, LiFe5O8 nanosized crystallites were synthesized by a novel and eco-friendly sol-gel process, by using powder coconut water as a mediated reaction medium. The dried powders were heat-treated (HT) at temperatures between 400 and 1000 °C, and their structure, morphology, electrical and magnetic characteristics, cytotoxicity, and magnetic hyperthermia assays were performed. The heat treatment of the LiFe5O8 powder tunes the crystallite sizes between 50 nm and 200 nm. When increasing the temperature of the HT, secondary phases start to form. The dielectric analysis revealed, at 300 K and 10 kHz, an increase of ε′ (≈10 up to ≈14) with a tanδ almost constant (≈0.3) with the increase of the HT temperature. The cytotoxicity results reveal, for concentrations below 2.5 mg/mL, that all samples have a non-cytotoxicity property. The sample heat-treated at 1000 °C, which revealed hysteresis and magnetic saturation of 73 emu g−1 at 300 K, showed a heating profile adequate for magnetic hyperthermia applications, showing the potential for biomedical applications.

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“…The obtained results are summarized in Table 1 . The average crystallite sizes of lithium ferrite crystal phase determined by the Scherrer method,

, uses the following Debye–Scherrer equation [ 49 ]:

where

is the diffraction angle, and β is the full width half maximum (FWHM) of the diffracted peaks, corrected by the relation

, where

and

are the experimental and the instrumental width. The instrumental width was determined using the LaB 6 powder standard pattern (SRM 660—National Institute of Standard Technology).…”

Section: Resultsmentioning

confidence: 99%

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

et al. 2021

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“…Bismuth orthoniobate (BiNbO 4 ) is still of interest after more than half a century due to its microwave dielectric and photocatalytic properties. , BiNbO 4 ceramics containing V 2 O 5 and CuO have excellent dielectric properties, as was shown for the first time in the work revealing high values of the quality factor Q r = 4260 (at 4.3 GHz), dielectric constant ε r = 43, and the coefficient of resonant frequency t f = +38 ppm/°C. In order to obtain high-density ceramics and optimize the dielectric properties of bismuth orthoniobate, sintering additives are added and bismuth or niobium atoms are substituted hetero- and isovalently. − The low temperature of the synthesis (∼1000 °C) of bismuth orthoniobate materials promotes their use as dielectrics for multilayer microwave circuits with silver (copper) inner conductors. Thus, bismuth orthoniobate materials facilitate miniaturization of the resonant devices…”

Section: Introductionmentioning

confidence: 99%

High-Temperature Crystal Chemistry of α-, β-, and γ-BiNbO₄ Polymorphs

et al. 2019

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Thermal behavior of the orthorhombic (α) and triclinic (β) polymorphs of BiNbO4 was studied by the methods of high-temperature powder X-ray diffraction (HTPXRD) and differential scanning calorimetry (DCS) in the temperature range 25–1200 °C. The study revealed the sequence of thermal phase transformations and the new high-temperature modification, γ-BiNbO4, which was formed above 1001 °C and existed up to the melting temperature of BiNbO4. The incongruent melting of BiNbO4 was characterized by the formation of the cubic phase with the approximate composition Bi3NbO7. The HTPXRD method was used in this study to evaluate thermal deformations and to calculate thermal-expansion coefficients (TEC) of the three modifications of BiNbO4 (α, β, and γ). The average volumetric TECs of these three modifications were in the range 19–36 × 10–6 °C–1. The triclinic phase β-BiNbO4 demonstrated the highest anisotropy of thermal expansion. α-BiNbO4 was characterized by the minimal TEC and anisotropy, which indicated its greatest stability. The crystal structure of γ-BiNbO4 was determined at 1100 °C using powder data and was refined using the Rietveld method (the α-LaTaO4 structural type, the space group Cmc21, a = 3.95440(3) Å, b = 15.0899(1) Å, c = 5.65524(5) Å, V = 337.458(5) Å3, R wp = 4.82, R Bragg = 3.61%). The methods of thermal analysis and high-temperature powder X-ray diffraction revealed that, during the heating, bismuth orthoniobate underwent the following sequence of phase transitions: α-BiNbO4 → γ-BiNbO4 → β-BiNbO4 and β-BiNbO4 → γ-BiNbO4 → β-BiNbO4 or, at slow heating, β-BiNbO4 → (α-BiNbO4) → γ-BiNbO4 → β-BiNbO4, where γ-BiNbO4 is the high-temperature phase of bismuth orthoniobate.

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“…The cavity resonant technique is frequently used to calculate the permittivity of materials in the microwave region. The introduction of a sample inside a resonant cavity provokes a perturbation of the electric field, with a shift of the resonance frequency (

Δ f = f_{0} - f_{l}

) which can be related with the real part of the complex permittivity ( ε ′).…”

Section: Methodsmentioning

confidence: 99%

Bi₂O₃–TiO₂–Nd₂O₃ lead‐free material for microwave device applications

Slavov

Teixeira

Graça

et al. 2018

Int J of Appl Glass Sci

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Lead-free Bi 2 O 3 -TiO 2 -Nd 2 O 3 system and its potential application for microwave devices applications were studied. The samples were synthesized using the melt quenching method. According to the X-Ray Diffraction analysis, the samples are polycrystalline with three different crystal phases. Measurements of the dielectric complex permittivity function were made at 2.7 GHz, using a resonant cavity and the small perturbation theory. The values of the dielectric permittivity of the prepared materials were compared with the commercial ones, and we conclude that these new lead-free materials have a good potential to replace lead-containing devices for microwave frequency applications.

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Microwave dielectric properties of (Bi1−xFex)NbO4 ceramics prepared by the sol–gel method

Cited by 17 publications

References 15 publications

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

High-Temperature Crystal Chemistry of α-, β-, and γ-BiNbO₄ Polymorphs

Bi₂O₃–TiO₂–Nd₂O₃ lead‐free material for microwave device applications

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Microwave dielectric properties of (Bi1−xFex)NbO4 ceramics prepared by the sol–gel method

Cited by 17 publications

References 15 publications

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine

High-Temperature Crystal Chemistry of α-, β-, and γ-BiNbO4 Polymorphs

Bi2O3–TiO2–Nd2O3 lead‐free material for microwave device applications

Contact Info

Product

Resources

About

High-Temperature Crystal Chemistry of α-, β-, and γ-BiNbO₄ Polymorphs

Bi₂O₃–TiO₂–Nd₂O₃ lead‐free material for microwave device applications