Dielectric constants of topaz, orthoclase and scapolite and the oxide additivity rule

Shannon, R. D.; Oswald, R.; Rossman, George R.

doi:10.1007/bf00202104

Cited by 7 publications

(3 citation statements)

References 29 publications

(18 reference statements)

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“…Although the measurement of individual ǫ s,⊥ and ǫ s, components for HAp has not been reported, our values are not far from ǫ s,⊥ = 10.5 and ǫ s, = 8.7 which were observed for crystalline fluorapatite. 75 The effective medium approximated dielectric constant is estimated as ǫ s,EMA = 11, regardless the exchange-correlation functional. The experimental static dielectric constant de-termined for HAp powder samples varies widely, and strongly depends on the porosity and amount of water within the samples.…”

Section: Propertymentioning

confidence: 99%

Optoelectronics and defect levels in hydroxyapatite by first-principles

Avakyan

Paramonova

Coutinho

et al. 2018

The Journal of Chemical Physics

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Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.

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Section: Propertymentioning

confidence: 99%

Optoelectronics and defect levels in hydroxyapatite by first-principles

Avakyan

Paramonova

Coutinho

et al. 2018

The Journal of Chemical Physics

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“…The identification of dc conductivity provides a quantifiable explanation of the behaviour of REEs during the electrostatic separation stage [2]. Moreover, the determination of the dielectric parameters (dielectric constant and loss, polarization, relaxation time and resonance frequency) can specify this behaviour [9][10][11][12][13][14]. Accurate and precise concentrations of REEs in the samples were obtained in a previous work [15,16].…”

Section: Introductionmentioning

confidence: 94%

Characterization of the electrical behaviour of rare earth elements during the upgrading of monazite

Radwan¹,

Fawzy²,

Ashry³

et al. 2004

J. Phys. D: Appl. Phys.

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Electrical properties of rare earth elements (REEs) in some geological materials were characterized during the upgrading of monazite from Egyptian black sand. It has been found that there was a significant relationship between concentrations of REEs and dc conductivity. Also, dielectric constant, dielectric loss, polarization, relaxation time and resonance frequency of samples containing REEs, were measured at a frequency range up to 1 MHz. From these measurements, it has been found that the values of electrical conductivity, resonance frequency and dielectric polarization are inversely proportional to the concentration of REEs. For most relations, the correlation coefficients were found to be better than 99%.

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“…Silicates are the most abundant mineral found on the earth’s surface, especially feldspar minerals . Generally silicates, aluminosilicates, and feldspar materials are reported to have a low dielectric constant value of approximately in the range of 3–8, and hence they are extensively used in semiconductor devices, microelectronics, and integrated circuits. − Various studies revealed that the dielectric constant considerably decreases with the increase in the silicate content within the structure. , Moreover, the presence of modifying cations such as K + , Na + , Mg 2+ , Ca 2+ , etc. and their consecutive migration within the structure determine the electrical properties of the aluminosilicates .…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Dielectric Properties of Naturally Formed Microcline and Kyanite: A Size-Dependent Study

Bardhan

Roy

Chanda³

et al. 2019

Crystal Growth & Design

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The present article reports the crystal defect-mediated changes in electrical characteristics, especially, dielectric properties, of naturally formed microcline and kyanite in two different size fractions. A facile top-down synthesis approach has been adopted to achieve the nanosized samples. Structural and morphological studies have been carried out using X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. Phase purity and microstructural characteristics of the samples were investigated by performing the Rietveld refinement method. Microstructural analysis reveals that the sample size has been greatly reduced to the nano regime after the mechanical ball-milling process, and the milling process eventually introduced some defects in the nanosized samples. UV−vis spectroscopy reveals the optical absorption characteristics and the band gap values of the samples. A major outcome of the present study is the enhancement of the defect states naturally formed samples using the mechanical milling method and the defect-mediated electrical response with varying temperature and frequency. Remarkably high dielectric permittivity values (77.3 × 10 3 for AF2 and 8.036 × 10 3 for KY2) in the nanosamples along with low tangent losses and good industrial feasibility of synthesis make the nanosized samples a potential material for fabricating lowcost energy storage devices.

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Dielectric constants of topaz, orthoclase and scapolite and the oxide additivity rule

Cited by 7 publications

References 29 publications

Optoelectronics and defect levels in hydroxyapatite by first-principles

Optoelectronics and defect levels in hydroxyapatite by first-principles

Characterization of the electrical behaviour of rare earth elements during the upgrading of monazite

Microstructure and Dielectric Properties of Naturally Formed Microcline and Kyanite: A Size-Dependent Study

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