A study of the crystallization process of Na1.6Zn0.8Si1.2O4 glass and the ionic conductivity properties of partially crystallized samples

The crystallization process of Na_1.6Zn_0.8Si_1.2O₄ glass was studied by means of differential scanning calorimetry, X-ray powder diffraction and the platinum/carbon replication technique. Partially crystallized samples were made by rapidly cooling samples from elevated temperatures using the DSC apparatus, and the ionic conductivity of the materials was determined by means of impedance measurements conducted at lower temperatures where the crystallization rate was negligible. The glass was found to crystallize at 830 K by precipitation and three-dimensional grain-growth of a crystobalite-type phase with the same composition as the glass. The overall activation energy for the crystallization process was determined from isothermal DSC measurements to be 340 kJ mol^–1. The bulk ionic conductivity for partially crystallized samples increases smoothly from 9.3 x 10^–5( cm)^–1 at 600 K for the glass to 2.4 x 10^–3( cm)^–1 for the crystallized material.     

Small polaron transport in V2O5–NiO–TeO2 glasses

Semiconducting glasses of the V₂O₅–NiO–TeO₂ system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10^–7 to 10^–1 S m^–1, indicating that the conductivity increased with increasing V₂O₅ concentration. A glass of composition 67.5V₂O₅–2.5NiO–30TeO₂ (mol %) having a conductivity of 2.47×10^–2 S m^–1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above _D/2 (_D: the Debye temperature); the electrical conduction at T>_D/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10^–7 to 5.48×10^–5 cm² V^–1 s^–1 at 400 K. The carrier density is evaluated to be 1.85×10¹⁹–5.50×10¹⁹ cm^–3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below _D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.     

Non-stoichiometric disorder in α-Nb2O5 at elevated temperatures

The electrical conductivity of polycrystalline-Nb₂O₅ was determined for the oxygen partial pressure range of 10⁰ to 10^–20 atm and temperature range 700 to 1150 ° C. The data were found to be proportional to the –1/6th power of the oxygen partial pressure for the oxygen pressure range 10^–20 to 10^–9 atm, and proportional toPO ₂ ^–1/4 for oxygen pressures greater than 10^–9 atm. The region of linearity where electrical conductivity varies as the –1/4th power of increased as the temperature was decreased. Thermogravimetric measurements were carried out in the temperature range 950 to 1250 ° C. The deviation from stoichiometry in-Nb₂O₅ (x in Nb₂O_5–x ) as a function of partial pressure of oxygen showed two distinct regions, namely a region with an approximately –1/6th dependence on and a region where the deviation was nearly independent of oxygen partial pressure. The electrical conductivity and thermogravimetric data are consistent with the presence of small amounts of acceptor impurities in-Nb₂O₅.     

Electrical conduction of partially stabilized zirconia Zr0.94Ca0.06O1.94 as a function of temperature and oxygen partial pressure

Partially stabilized zirconia (PSZ), Zr_0.94Ca_0.06O_1.94was prepared by a hot kerosene drying method and a conventional oxide wet-mixing method. The total d.c. conductivities of these zirconia specimens were measured by the three-terminal technique as a function of temperature in the range 1088 to 1285 K and oxygen partial pressure in the range 1 to 10^–24 bar. The specimen prepared by the hot kerosene drying method showed near oxygen ion conduction with four times higher conductivity than the specimen prepared by the conventional mixing method at T=1088–1285 K and bar. The higher oxygen pressure conductivity tended approximately towards a to dependence, indicative of p-type conduction, whereas the lower oxygen pressure conductivity tended to be virtually independent of oxygen pressure, indicative of oxygenion conduction. The activation energy was found to be 130 kJ mol^–1 at T=1088–1285 K, bar (air) for pure electron-hole conduction and 153kJ mol^–1 at T=1088–1285 K for ionic conduction.     

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part II Electrical transport behavior

Electrical transport behaviour of the valence compensated system Ca_1–x La _x Ti_1–x Cr _x O ₃ (x 0.50) has been investigated by studying the Seebeck co-efficient, DC and AC conductivity as a function of temperature. Seebeck co-efficient, DC conductivity of different compositions has been measured in the temperature range 300 K–1000 K. AC conductivity for different compositions were determined in the temperature range 100–550 K and frequency range 10 Hz–10 MHz. Positive values of Seebeck co-efficient show that holes are the majority charge carriers. Conduction seems to occur by correlated barrier hopping of holes among Cr³⁺and Cr⁴⁺ions or V_O and V_O . Almost equal values of activation energies obtained for DC conductivity and dielectric relaxation process show that both the processes occur by the same mechanism.     

Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

Oxygen ion conduction in γ-Bi2O3 doped with Sb2O3

Electrical conduction in bcc-Bi₂O₃ doped with Sb₂O₃ was investigated by measuring electrical conductivity, as a function of temperature and oxygen partial pressure , and ionic transference number. The-Bi₂O₃ doped with 1 to 3 mol% Sb₂O₃ was stable up to 550° C and showed an oxygen ionic conduction in the region of 10⁵ to 10^–9 Pa. As the Sb₂O₃ content increased, ionic conductivity increased up to 2.5 mol % Sb₂O₃ (1.8×10^–3–1cm^–1 at 500° C) and then decreased. However, the activation energy for ionic conduction remained almost unchanged. It was proposed that the-Bi₂O₃ contains a lot of oxygen vacancies and incorporated Sb⁵⁺ ions at tetrahedral sites which affect the concentration of oxygen vacancy effective for conduction.     

Doping of calcium titanate with chromium and indium

The lattice parameters and composition range of orthorhombic CaTi_{1 – x} Cr_xO_{3 –} solid solutions were determined by x-ray powder diffraction. Samples with the nominal compositions CaTi_{1 – y} In_yO_{3 –} , synthesized in the range y=0.05–0.3, consisted of two phases: CaTiO_{3 –} and a CaIn₂O₄-based phase. The compositions of the synthesized phases were checked by x-ray microanalysis. The electrical conductivity of the CaTi_{1 – x} Cr_xO_{3 –} (0 < × 0.2)solid solutions was measured as a function of oxygen partial pressure (0.21 × 10⁴ to 1.0 × 10^–11 Pa) at 900 and 1000°C. Cr doping of calcium titanate was shown to increase its conductivity. A mechanism of defect formation in doped calcium titanate was inferred from conductivity versus data.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 475–478.Original Russian Text Copyright © 2005 by Murashkina, Demina.     

Electrical properties of In doped CdS thin films

Indium doped polycrystalline cadmium sulphide CdS:In thin films have been prepared by the spray pyrolysis technique on glass substrates in an enclosed dome. The different scattering mechanisms such as lattice, impurity and grain boundary scattering for CdS:In films are observed at low temperature, in the range of 303 to 120 K. The experimentally determined mobilities due to these scatterings are well interpreted with those of theoretically calculated mobilities. The d.c. conductivity for CdS:In films has also been studied in the same temperature region. The Mott variable range hopping conduction process followed below the temperature of 150 K. The Mott parameters such as N(E _F ), R, W and are found to be 1.26 × 10¹⁹ eV^–1cm^–3, 9.8 × 10^–-7cm, 0.02 eV^–1 and 2.38 × 10⁶cm^–1, respectively from the conductivity data.     

Proton conducting polymer electrolyte: II poly ethylene oxide + NH4l system

A new proton conducting polymer electrolyte PEO + NH₄l system has been investigated. The solution-cast films of different stochiometric ratios have been prepared and characterized. Proton transport has been established using various experimental studies, namely optical microscopy, X-ray diffraction, differential thermal analysis, infrared, coulometry transient ionic current and electrical conductivity measurements at different temperatures and humidity. The maximum conductivity of the complexed material has been found to be 10^–5 S cm^–1. Both H⁺ ion and I^– anion movements are involved with respective transference numbers and mobilities ast _H+=0.74, ,t _l–=0.09, _H+=4.97 × 10^–6 cm² V^–1 s^–1 and _l–=7.65.     

Dielectric spectra of fresh cement paste below freezing point using an insulated electrode

The spectra of complex dielectric constant were measured on a fresh cement paste with a water/cement ratio of 0.4 sandwiched between insulated electrodes in the frequency range 10 kHz–1 MHz and temperature range between 0 °C and — 30 °C. The bulk dielectric constant, 30–20, and conductivity, 6.14×10^–5–0.65×10^–5, in the temperature range –10 to –28 °C were much lower than those at room temperature, owing to the great decrease of ionic mobility caused by freezing the cement paste. The activation energy of 0.31 eV for the ionic conduction in fresh cement paste was obtained from an Arrhenius plot of conductivity at subzero temperature.     

Effect of Crystal Structure on the Electrical Properties of CaTi1 – xFexO3 – δ

The electrical conductivity of CaTi_{1 – x} Fe _x O_{3 –} (x= 0–0.5) was measured as a function of temperature and oxygen partial pressure. At 1000°C, the highest conductivity was observed at x= 0.2. The crystal structure of the materials with x= 0, 0.2, 0.25, and 0.3 was studied by x-ray powder diffraction and refined by the full-profile analysis method. The results were used to elucidate the mechanisms of the high-temperature (1000°C) formation, ordering, and transport of oxygen vacancies in CaTiO₃upon substitution of Fe³⁺for Ti⁴⁺. The composition dependences of ionic conductivity calculated for CaTi_{1 – x} Fe _x O_{3 –} agree well with experiment.     

Preparation, characterization and conductivity studies of AgI-Ag2O-(TeO2 + P2O5) fast ionic conducting glasses

Silverphosphotellurate (SPT) quaternary fast ionic conducting (FIC) glasses of compositions AgI-Ag₂O-[(1 – x)P₂O₅ + xTeO₂], x = 0.0 to 1.0 in steps of 0.1, were prepared by melt quenching. All SPT compounds were characterized by X-ray diffraction and the amorphous nature of the samples was confirmed. The structure of all compositions was examined by Fourier Transform Infrared Spectroscopy. The glass transition temperature (T _g) was determined for all SPT samples, using differential scanning calorimetry. Complex impedance measurements were made on all glasses in the frequency range 40 Hz to 100 kHz. Impedance data were analyzed using Boukamp equivalent circuit software and the bulk conductivity was obtained. The highest conductivity ( = 1.59*10^–2 S/cm) was shown by the composition 60%AgI – 26.67%Ag₂O – 13.33% (0.3P₂O₅ + 0.7TeO₂).     

Electrical conductivity in non-stoichiometric titanium dioxide at elevated temperatures

The electrical conductivity of polycrystalline titanium dioxide prepared by a liquid mix technique was measured for the oxygen partial pressure range of 10° to 10^–19 atm and temperature range of 850 to 1050° C. The data were found to be proportional to the –1/6 power of oxygen partial pressure for the oxygen pressure range 10^–19 to 10^–15 atm, and proportional to for the oxygen pressure range >10^–15 atm. The region of linearity where the electrical conductivity varied as the –1/4 power of increased as the temperature was decreased. There was evidence of p-type behaviour for 10^{ - 2}$$ " align="middle" border="0"> atm in the temperature range 950 to 850° C, although the measured data were insufficient to assign a pressure dependence. Electrical conductivity minima in the log against log plot moved to lower as the temperature was decreased in the range 950 to 850° C. The measured oxygen pressure dependence of electrical conductivity in the lowest region supports the oxygen vacancy defect model. The observed data are consistent with the presence of very small amounts of acceptor impurities. A binding energy of 0.67 eV between the acceptor impurity and its compensating oxygen vacancy was also determined.     

Determination of the thermal conductivity of polypyrrole over the temperature range 280–335 K

Samples of polypyrrole were synthesised under galvanostatic conditions to produce films possessing a range of electrical conductivity from 10^–3 to 10 S cm^–1. The electrical and thermal conductivity of these films has been determined between 280 and 335 K. The electrical conductivity was measured using a four probe technique calibrated against ASTM D4496-87. Thermal conductivity was determined from measurements of thermal diffusivity, specific heat and density. Thermal diffusivity was determined using a modified a.c. calorimetry technique, while differential scanning calorimetry (DSC) was used to determine specific heat. The polymer's density was measured using Archimedes' principle. The results were used to calculate the Lorenz number of polypyrrole. A comparison of the predicted behaviour and experimental results was made. Thermal conductivity is found to be large compared to that predicted from the electrical conductivity measurements on low conductivity films. Molecular vibration effects are found to be non-trivial and experimental means for measuring their contribution are mentioned. While polypyrrole has been regarded as a synthetic metal the thermal conductivity results show this classification is wrong.     

Electric conductivity and oxygen permeability of modified cerium oxides

Electrical conductivities of samarium (Sm), terbium (Tb), praseodymium (Pr) and zirconium (Zr) doped ceria membranes were measured in T = 600–900°C and pO₂ = 10^–22–0.21 atm. Doping Sm and Pr in CeO₂ respectively enhances the ionic conductivity and electron-hole conductivity of ceria. Sm-Pr doped ceria exhibits both n-type (at lower pO₂) and p-type (at high pO₂) electronic and ionic conductivity in the temperature range studied. Adding Tb in the Sm doped ceria causes a reduction in ionic conductivity. Zr-Pr doped ceria is an n-type electronic conductor at low and p-type electronic conductor at high pO₂. The ionic conductivity of Zr-Pr doped ceria is lower than Sm doped ceria but higher than pure ceria. Oxygen permeation flux through the Zr-Pr doped ceria membrane, dominated by the slow oxygen ionic conduction, is similar to the ytttria doped bismuth oxide membrane, and smaller, but close to that of perovskite-type lanthanum cobaltite membrane.     

D. C. electrical properties of hot-pressed nitrogen ceramics

The d.c. electrical properties of some hot-pressed polycrystalline nitrogen ceramics have been measured between 18 and 500° C in applied electric fields up to 1.1×10⁴ Vcm^–1. The materials examined were Si₃N₄, 5wt%, MgO/Si₃N₄ and two sialons havingz=3.2 andz=4.0. The conduction in all the materials showed similar general features. The time dependent charging (I _c) and discharging currents (I _D) were observed which followed a I(t)t_–n law at room temperature withn=0.7 to 0.8. The exponentn forI _c decreased with increasing temperature. The current density-field (J _s-E) characteristics were ohmic in applied fields of less than 3×10³ Vcm^–1; conductivity increased with electric field above that range. Above about 280° C, a was independent ofE, its temperature dependence following log T ^–1. Below about 230° C conductivity fitted a exp (–B/T _1/4) law in both low and high fields. There is a good correlation between the temperature and field variations of time dependent current and the steady current. The conductivities were in the range of 10^–15 to 10^–16–1 cm^–1 at 18° C and rose to 4×10^–10 to 2×10^{–12 –1} cm^–1 at 500° C. The activation energies were in the range of 1.45 to 1.80 eV and 0.05 to 0.15 eV at above 300° C and near room temperature respectively. Various models to explain the data are considered.     

Defect structure of acceptor-doped calcium titanate at elevated temperatures

The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to for the oxygen pressure range < 10^–10 atm and proportional to for the oxygen pressure range ( 10^–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO₃. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO₃. The defect chemistry of CaTiO₃ is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation.     

A model for internal pressurization in cationic solid electrolytes

The possibility of internal pressurization in a cationic solid electrolyte is examined by analysing a three-compartment cell consisting of two solid electrolyte membranes with different ionic and electronic conductivities. The pressure generated in the central chamber is related to the ionic and electronic conductivities of the membranes, the thicknesses of the membranes as well as the current density. By identifying the appropriate equivalent circuit for the three-compartment cell, the transient problem of pressurization is also solved. Finally, the probability of degradation of sodium--alumina used in Na-S cells is assessed using published values of electronic conductivity. The calculations indicate that the pressure generated can be large if the electronic conductivity of sodium-alumina in contact with molten sodium is greater than 10^–3 (ohm m)^–1. Published work, however, indicates that the electronic conductivity at 350° C is 8×10^–10 (ohm m)^–1. Therefore, degradation due to internal pressurization is unlikely. However, on the other hand, it is conceivable that certain impurities or stabilizing elements may impart higher electronic conductivities. Consequently, the chemical composition of sodium--alumina may be an important factor in relation to long-term operation.     

Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C. The electrical conductivity () of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives = 10^–3 S cm^–1 at 25° C. Infrared, nuclear magnetic resonance (¹H and¹³C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH⁺-group in the reaction of nylon 6 with iodine. The temperature dependences of of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol^–1 depending on the iodine content. Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity. Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or -electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10^–5 to 10^–2 S cm^–1. Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 1.5 X 10^–2 S cm^–1 when the adducts contain about 90 wt% iodine.