Cation arrangement in a few oxides with crystal structures of the spinel type

Verwey, E. J. W.; Boer, J. H. de

doi:10.1002/recl.19360550608

Cited by 455 publications

(126 citation statements)

References 14 publications

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“…The electrical conduction in ferrites can be explained by the Verwey model of electron hopping (Verwey and de Boer 1936) which involves exchange of electrons between ions of the same element present in different valence states, and distributed randomly over crystallographically equivalent lattice sites. In the present system, the conduction is taken to be due to the exchange of 3d electrons between ferrous (Bradley 1971).…”

Section: Frequency F(khz)mentioning

confidence: 99%

Dielectric and electrical properties of Cr substituted Mg ferrites

Zakaria

Nesa

Khan

et al. 2015

J Bangladesh Acad Sci

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The spinel ferrites MgCr x Fe 2-x O 4 (0.0    1.0) were prepared through the solid state reaction using conventional ceramic method at 1300C in air. The homogeneous phase of the ferrite samples was observed from the X-ray diffraction study. Lattice parameter of the samples was found to decrease with increasing Cr concentration in the system obeying Vegard's law. The ac electrical resistivity, measured as a function of temperature, decreases with the increase of temperature indicating the semiconducting nature of all the samples. The activation energies were calculated and found to decrease with increasing Cr content. The lower activation energies are associated with higher electrical conductivity. With the increase of temperature, dielectric constant () and dielectric loss tangent are observed to be increased; while with the increase of frequency, dielectric constant () and dielectric loss tangent decrease for all the samples.

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Section: Frequency F(khz)mentioning

confidence: 99%

Dielectric and electrical properties of Cr substituted Mg ferrites

Zakaria

Nesa

Khan

et al. 2015

J Bangladesh Acad Sci

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“…Since the mean oxidation state of Mn in LiMn 2 O 4 is +3.5, the simplest scheme would be a disproportionation into Mn 3+ and Mn 4+ in equal fractions. However, the spinel-type structure, where the B-site ions are located at the nodes of a corner-linked tetrahedral network, does not allow alternative (Verwey and de Boer 1936;Verwey and Haayman 1941;Sasaki 1997;Senn et al 2012). The structural complexity of the low-temperature LiMn 2 O 4 thus arises from frustrated charge disproportionation on the tetrahedral B-site network, which has not been fully solved to date.…”

Section: Introductionmentioning

confidence: 99%

Bond-length fluctuation in the orthorhombic 3 x 3 x 1 superstructure of LiMn2O4 spinel

Ishizawa

Tateishi²,

Oishi

et al. 2014

American Mineralogist

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Single-crystal synchrotron X-ray diffraction experiments are conducted on spinel-type LiMn 2 O 4 at 230 and 320 K to investigate the effect of charge disproportionation of Mn ions on phase transition near room temperature. The orthorhombic 3a c × 3a c × 1a c superstructure of the low-temperature form, where "a c " is the ideal cubic cell edge, has a network of Mn 4+ ions at the vertices of a slightly distorted truncated square tessellation comprising one square and two octagonal prisms; the square prism and one type of octagonal prism house Mn 3+ ions with Jahn-Teller (JT) elongated Mn-O bonds almost parallel to the c and b axes, respectively, whereas the other octagonal prism houses Mn ions with JT-induced bond-length fluctuation for the Mn-O bonds lying almost parallel to the a axis. The Mn ions in the latter octagonal prism are assumed to exchange their oxidation states dynamically between 3+ and 4+ in a time ratio of ~3:1, forming a polaron centered at a Mn 4 O 4 heterocubane cluster with orbital and spin orders. The high-temperature cubic form contains an inherent positional disordering of oxygen ions. The effect of the molecular polarons on the phase transition mechanism is discussed on the basis of a spin blockade in the form of truncated square tessellation.

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“…The electrical conduction in zinc ferrite can be explained on the basis of Verwey mechanism [8] involving electron exchange between ions of the same element which are present in more than one valence state and distributed randomly over crystallographically equivalent lattice sites. Depending upon the sintering conditions, a number of such ions may be produced during the preparation of ferrite samples.…”

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confidence: 99%

Effect of aluminium substitution on electrical conductivity and physical properties of zinc ferrite

Prakash

1987

J Mater Sci Lett

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The polycrystalline ferrites, which have high resistivity and low eddy current losses, play a useful role in many technological applications ranging from microwave frequencies to radio frequencies. Their properties are strongly dependent on the method of preparation and the amount and type of substitution. A detailed study has been carried out on the relationship between structure and various properties of ferrites [1]. Several investigators have studied the influence of cadmium [2], chromium [3], titanium [4] and tin [5,6] substitution on the properties of zinc ferrite. Recently, Prakash [7] reported a M6ssbauer effect study of trivalent aluminium-substitution zinc ferrite. The aim of the present work is to investigate the effect of A13+ substitution on electrical conductivity and other physical properties of zinc ferrite.Ferrite samples of composition ZnAlxFe2_xO4 (x = 0 to 1.2, in steps of 0.3) were prepared by the standard dry ceramic method. Details of the preparation were given in an earlier publication [7]. X-ray diffraction results showed the presence of a single spinel phase in all the samples. Lattice parameters were calculated from the observed d values. The X-ray density was determined using the formula dx = 8M/(Na 3) where M is the molecular weight, N the Avogadro number and a the lattice constant. The experimental density of the samples was determined using the method of hydrostatic weighing. The electrical conductivity measurements were carried out by means of a two-probe d.c. method. Electrical contacts were made using an air-dried silver epoxy. Measurements were made as a function of composition and temperature.The variation of lattice constant, a, with aluminium concentration, x, is shown in Fig. 1: the lattice constant decreases with increasing x. The variation can be explained on the basis of ionic radii of the substituted ions. If the radius of the substituted ion is smaller than that of the displaced ion, the lattice shrinks and the lattice constant decreases. Because the ionic radius of A13+ (0.051 nm is smaller than that of Fe 3+ (0.067 nm), the lattice constant is expected to decrease with increasing aluminium concentration. Fig. 2 shows the variation of experimental density, d, percentage shrinkage, s, and porosity, p, with aluminium content. The linear percentage shrinkage, during sintering, in the diameter of the discs decreases with increasing substitution level, x. The highest value (15.1%) was obtained for ZnFezO4 (x = 0). The same sample shows the highest density. The smallest shrinkage was found for the sample with x = 1.2 (= 1.3%). From the figure it is clear that the density of the samples

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Cation arrangement in a few oxides with crystal structures of the spinel type

Cited by 455 publications

References 14 publications

Dielectric and electrical properties of Cr substituted Mg ferrites

Dielectric and electrical properties of Cr substituted Mg ferrites

Bond-length fluctuation in the orthorhombic 3 x 3 x 1 superstructure of LiMn2O4 spinel

Effect of aluminium substitution on electrical conductivity and physical properties of zinc ferrite

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