Electrical conductivity and thermoelectric power of nickel-zinc ferrites

Electrical conductivity (σ) and thermoelectric power (Q) of polycrystalline nickel-zinc ferrites of different compositions was investigated as a function of composition and temperature. The electrical conductivity in these ferrites is explained on the basis of the hopping mechanism. Plots of log (σT) versus 10³/T are almost linear and show a transition near the curie temperature. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region. The carrier concentration and mobility of charge carriers has been discussed as a function of composition and temperature.     

Electrical conductivity and thermoelectric power of lithium-cadmium ferrites

The electrical conductivity (σ) and thermoelectric power (Q) of polycrystalline lithiumcadmium ferrites having the chemical formula Li_0.5–x/2Cd_xFe_2.5–x/2O₄ where (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) have been investigated as a function of temperature. Lithium-cadmium ferrite with x = 0.4 is found to possess minimum electrical conductivity and lowest Seebeck coefficient. Plots of log (σT) versus 10³T are almost linear and have shown a transition near the Curie temperature except in the case of cadmium ferrite. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The values of charge carrier concentration and mobility have also been computed. The properties of cadmium-substituted lithium ferrites have been correlated with those of zinc-substituted lithium ferrites, cadmium and zinc being two non-magnetic divalent ions occupying essentially tetrahedral A sites when substituted in ferrites.     

Electrical conductivity and thermoelectric power in amorphous As2Se3Tlx semiconductors

Dc conductivity and thermopower measurements as a function of temperature have been performed on solid As₂Se₃Tl_x glasses with x ranging from 0 to 1.99. Investigations have been extended to low temperatures. By substitution of Tl the conductivity can be increased by more than 5 orders of magnitude without changing the type of transport mechanism. Band-like conduction is observed with holes being the dominant charge carriers. The three-dimensional network of As₂Se₃ is assumed to be modified by the Tl atoms; this leads mainly to a decrease in the activation energy.     

Electrical conductivity and dielectric properties of Bi2O3-GeO2-PbO-MoO3 glasses

Glasses having compositions 40Bi₂O₃-20GeO₂-(40−x)PbO-xMoO₃ (where x = 3, 6, 9, 12 and 15 mol%) were prepared by normal melt quenching technique. The density (d) decreases gradually with the increase of the MoO₃ content in such glasses. This may be due to the lower molecular weight MoO₃ is substituted by a higher molecular weight PbO. The dc conductivity decreases while the activation energy increases with the increase of the MoO₃ content. The dc conductivity in the present glasses is electronic depends strongly upon the average distance, R, between the Mo ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. Dielectric properties (constant ε, loss tan δ, ac conductivity σ_ac, over a range of frequency 0.12-100 kHz and temperature 325-650 K and frequency exponent s) of these glasses have been studied.     

Electrical conductivity of NbN-SiO2 films obtained by ammonolysis of Nb2O5-SiO2 sol-gel derived coatings

The studies of electrical conductivity of NbN-SiO₂ films are reported. To obtain these films, sol-gel derived xNb₂O₅-(100 − x)SiO₂ (where x = 100, 90, 80, 70, 60, 50 mol%) coatings were nitrided at 1200 °C. The nitridation process leads to the formation of some disordered structures, with NbN metallic grains dispersed in insulating SiO₂ matrix. The structure of the samples was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical conductivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The superconducting transition was not observed even for the sample that does not contain silica. All the samples exhibit negative temperature coefficient of resistivity. The results of conductivity versus temperature may be described on the grounds of a model proposed for a weakly disordered system.     

Ionic conductivity of Li2O-BaO-Bi2O3 glasses

Dc and ac conductivities of Li₂O-BaO-Bi₂O₃ glasses have been studied in a temperature range of 263-523 K and a frequency range of 10 Hz-2 MHz and have been compared with those of binary Li₂O-Bi₂O₃ glasses. The frequency dependent conductivity has been studied employing both the modulus and conductivity formalisms. We have observed small changes in the dc conductivity and its activation energy from those of the binary glass when content of BaO is small. However we have observed noticeable changes in the conductivity and the activation energy when BaO content is large. The significant changes in the values of the non-exponential parameter and the power-law exponent of the ac electrical properties have been observed due to introduction of BaO in the lithium bismuthate glasses. The existing relation between the power-law exponent and the non-exponential parameter was also violated in the present glass compositions.     

Low-temperature specific heat of amorphous and crystalline Te0.81Ge0.15As0.04

We have measured the specific heats of amorphous and crystalline specimens of Te_0.81Ge_0.15As_0.04 between 0.2 and 20 K, and of crystalline Te_0.93As_0.07 between 1 and 20 K. Amorphous Te_0.81Ge_0.15As_0.04 shows a low-temperature linear specific heat anomaly whose magnitude, 0.027 mJ/mol-K², is similar to that of other amorphous insulators. Crystalline Te_0.81Ge_0.15As_0.04 exists as a two-phase material comprised of GeTe and As-doped Te. The specific heat of this material is analyzed in terms of a weighted average of the properties of its two constituents.     

High-field conductivity in SnO2 glazes

The conductivity of glazes consisting of SnO₂ in Sb-doped BaAl-borate and BaAl-borosilicate glasses has been studied for fields in the range 10²–10⁵ V/cm at temperatures 4.2 K ? T ? 470 K. The glazes were free of mobile ions such as K, Na, Li and Pb. Conduction takes place between Sb-doped SnO₂ particles concentrated in the fused contact region between the much larger glass particles. At high temperatures (300–470 K), the conductivity is thermally activated of the Frenkel-Poole type. At 77 K, both tunneling and thermally activated conductivity appear to be present.     

Pressure and temperature dependence of the electrical resistivity of bulk Al23 Te77 glass

Electrical resistivity of bulk amorphous Al₂₃T₇₇ samples has been studied as a function of pressure (up to 80 kbar) and temperature (down to 77 K). At atmospheric pressure the temperature dependence of resistivity obeys the relation ? = π₀ exp(δE/RT) with two activation energies. In the temperature range 300 K ? T > 234 K the activation energy is 0.58 eV and for 234 >T ? 185 K the value is δE = 0.30 ev. The activation energy has been measured as a function of pressure. The electrical resistivity decreases exponentially with the increase of pressure and at 70 kbar pressure the electrical behaviour of the sample shows a metallic nature with a positive temperature coefficient. The high pressure phase of the sample is found to be a crystalline hexagonal phase.     

Structure and electrical conductivity of new Li2O-CeO2-B2O3 glasses

Fourier transformation infrared spectra, density and DC electrical conductivity of 30Li₂O · xCeO₂⋅(70 − x)B₂O₃ glasses, where x ranged between 0 and 15 mol%, have been investigated. The results suggested that CeO₂ plays the role of network modifier up to 7.5 mol%. At higher concentrations it plays a dual role; where most of ceria plays the role of network former. The density was observed to increase with increasing CeO₂ content. The effect on density of the oxides in the glasses investigated is in the succession: B₂O₃ < Li₂O < CeO₂. Most of CeO₂ content was found to be associated with B₂O₃ network to convert BO₃ into B O₄⁻ units. The contribution of Li⁺ ions in the conduction process is much more than that due to small polarons. The conductivity of the glasses is mostly controlled by the Li⁺ ions concentration rather than the activation energy for CeO₂ > 5 mol%. Lower than 5 mol% CeO₂ the conductivity is controlled by both factors. The dependence of W on BO₄⁻ content supports the idea of ionic conduction in these glasses.     

AC conductivity of (As2Te3)95Ge5

The elctrical conductivity of amorphous chalcogenide (As₂Te₃)₉₅Ge₅ is investigated at variable frequency, from 1 kHz up to 35 GHz, and a variable temperature, from 77 to 300 K. The low-temperature conductivity is constant with temperature at a fixed frequency. At a fixed temperature, it obeys a ω^0.8 law only at low frequencies. The results are analysed with respect to the polaron problem, but also with a simple model of several dilute localized levels having a wide energy distribution in the forbidden band.     

The structure of liquid As2Se3 and GeSe2 by neutron diffraction

The liquid structures of As₂Se₃ and GeSe₂ have been investigated using the neutron diffraction patterns. In both cases the structure factor showed a low first peak maximum which follows a weak but apparent pre-peak at very low momentum transfer. It was also observed that the radial distribution function of both materials are characterized by the well-defined first neighbor shell because of the deep minimum on its right-hand side although in the liquid state. These results indicate that strong covalent bondings between unlike atoms in the solid state still remain when melting. Both the structure factor and the distribution curves of these alloys are, on the whole, similar to those in the amorphous phase which have already been examined. A slight difference in the coordination number, however, is found between amorphous and liquid phases of these materials.     

Electric conductivity of glasses in the system Na2O/CaO/SiO2/Fe2O3

The addition of polyvalent transition metal ions to the usually insulating traditional soda-lime-silica glasses can lead to semiconducting properties. We report on synthesis of glasses and glass-ceramics in a soda-lime-silicate based system containing Fe₂O₃ in the concentration range from 5 to 30 mol%. Two sub-systems were considered, in one of them the ratio [Na₂O]/[Fe₂O₃] was varied while in the other one, the ratio [SiO₂]/[Fe₂O₃] was changed. The phase composition of the synthesized products was characterized by X-ray diffraction and energy dispersive X-ray analysis, while the electrical properties were studied by impedance spectroscopy. Partially crystallized non-reduced samples are semiconducting even at room temperature while the glassy samples (both reduced and non-reduced) exhibit semiconducting properties at temperatures equal or larger than 100 °C. An attempt is done to predict the physical approximation explaining the conduction process in the glasses.     

Ionic conductivity of Li2OB2O3 thin films

The ionic conductivity of evaporated Li₂OB₂O₃ thin films has been studied. These thin films were found to show a considerably high ionic conductivity of 1 × 10^?7 Ω^?1 cm^?1 at room temperature. The conductivity increases with increasing Li content and exhibits a maximum value near 3Li₂O·B₂O₃. The structure of these films was determined using infrared absorption and laser Raman scattering spectroscopy. Using the results, the correlation between structure and conductivity is also discussed.     

The dielectric behavior of a thermoelectric treated B2O3-Li2O-Nb2O5 glass

A transparent glass with the composition 60B₂O₃-30Li₂O-10Nb₂O₅ (mol%) was prepared by the melt-quenching technique. Glass-ceramics, containing LiNbO₃ ferroelectric crystallites, were obtained by heat-treatment (HT) above 500 °C, with and without the presence of an external electric field. The dielectric properties of the glass and glass-ceramic were investigated, as a function of temperature (270-315 K), in the 10 mHz-32 MHz frequency range. The presence of an external electric field, during the heating process, improves the formation of LiNbO₃ crystallites. The rise of the treatment temperature and the applied field, during the heat-treatment, leads to a decrease in the dc electric conductivity (σ_dc), indicating a decrease of the charge carriers number. The dielectric permittivity (ε′) values (300 K;1 kHz) are between 16.25 and 18.83, with the exception of the 550 °C HT sample that presents a ε′ value of 11.25. An electric equivalent circuit composed by an R in parallel with a CPE element was used to adjust the dielectric data. The results reflect the important role carried out by the heat-treatment and the electric field during the HT in the electric properties of glass-ceramics.     

Ac conductivity of Ag-doped bulk,glassy As2S3

Measurements of the electrical conductivity of Ag-doped bulk As₂S₃ glasses have been made as functions of temperature, pressure, frequency and Ag doping level. A Debye-like loss peak was observed near 10⁴ Hz. The frequency of the loss peak is dependent on temperature, pressure and doping level, but these dependences are different from those of the dc conductivity. The ac loss is attributed to the Maxwell-Wagner losses characteristic of inhomogeneous materials. The materials are presumed to be inhomogeneous mixtures of As₂S₃ and Ag₂S. We have also searched unsuccessfully for ac conductance in several bulk chalcogenide glasses.     

EXAFS studies of glassy and liquid ZnCl2: A comparison with vitreous GeO2

The Zn-EXAFS (extended X-ray absorption fine structure) above its K-absorption edge has been measured for glassy ZnCl₂ at low temperature, through T_g (375 K), and into the supercooled and normal liquid state (mp = 593 K) at 673 K. By Fourier filtering and fitting the normalized glass spectra using α-ZnCl₂ as a model compound, the Zn²⁺Cl^? distance was determined to be (2.34 ± 0.01) Å and the average coordination number about the Zn²⁺ was found to be 5.1 ± 0.8. The latter value agrees with the value of 4.7 nearest neighbors obtained by the molecular dynamics computer simulation study of Woodcock et al., for liquid ZnCl₂ just above its melting point. The agreement is supportive of the notion that short-range order in the glass is reflective of that of the corresponding liquid from which it was quenched. Spectral measurement as a function of temperature indicates that there is considerable dynamic decoupling of the Zn²⁺ from its nearest Cl^? neighbor even below T_g. This is contrasted with similar data in glassy GeO₂ which show that the motion of Ge is strongly coupled with its four oxygen neighbors all the way to T_g. This difference in dynamic disorder substantiates the notion that glassy ZnCl₂, as well as vitreous BeF₂, provides a further weakened structural analog for glassy GeO₂ and SiO₂.     

Electrical characteristics of materials in the BaO---Fe2O3---B2O3 system

Structural peculiarities, as for example segregation and crystallization in vitroceramic materials, may have a significant influence on the electrical volume resistance of materials. Interesting characteristics can be detected in the case of the system BaO---Fe₂O₃---B₂O₃. This paper presents results showing that very different conductivity behaviours can be obtained by a suitable modification of the composition of the materials and by heat treatment.     

Electrical and photoconductive properties of the As2---Se3---Bix system

The electrical and photoconductive properties of amorphous As₂---Se₃---Bi_x compact samples were studied. The thermal activation energy decreases slightly and the dark conductivity increases with increasing Bi concentration within the region of glass formation which is less than 5 at.%. Photoconductive spectral distribution showed a peak for all bulk samples. A band model can be used to explain these results.     

Synthesis and X-ray structural investigation of K2(H5O2)[UO2(C2O4)2(HSeO3)]

The synthesis and X-ray diffraction analysis of K₂(H₅O₂)[UO₂(C₂O₄)₂(HSeO₃)] single crystals have been performed. This compound crystallizes in the triclinic system with the unit-cell parameters a = 6.7665(4) ?, b = 8.8850(4) ?, c = 12.3147(7) ?, α = 94.73°, β = 90.16°, γ = 92.11°, sp. gr. P[`1]P\bar 1, Z = 2, and R = 0.019. The basic structural units are island [UO₂(C₂O₄)₂(HSeO₃)]³⁻ groups, which belong to the AB ₂⁰¹ M ¹ crystallochemical group of uranyl complexes (A = UO₂²⁺, B ⁰¹ = C₂O₄²⁻, and M ₁ = HSeO₃⁻). Uraniumcontaining complexes are linked through K⁺ and H₅O₂⁺ ions and via a system of hydrogen bonds with the participation of oxonium hydrogen atoms in this structure.