Electrical properties and proton conduction of gadolinium doped ceria

The electrical properties and proton conduction of Gd_0.1Ce_0.9O_1.95 (10GCO) were investigated via impedance spectroscopy in different atmospheres and various gas concentration cells. In oxygen atmosphere, GCO is nearly a pure oxygen ionic conductor, while in hydrogen GCO behaves as a mixed conductor of oxygen ions, electrons and protons. Depending on the temperature, the total conductivity is usually enhanced by one to two orders of magnitude in hydrogen than in air/oxygen due to mixed conduction. By examining ionic transport properties of oxygen ions and protons using gas concentration cells we have discovered that the ionic transport properties depend largely on the gas atmospheres and change from one type to the other. Proton conduction generally exists in GCOs, and becomes significant in hydrogen atmospheres, which normally results in a contribution between 5 to 10 % of the total conductivity for 10 GCO. A maximum value of 17 % of the contribution by protons has been observed. The reduction of Ce⁴⁺ to Ce³⁺ of the sample in reduced atmospheres causes the formation of additional oxygen vacancies and electrons, associated also with the creation of protons. All these charge carriers are responsible for the electrical and transport properties of the investigated GCO materials. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Electric conduction properties of boron-doped ceria

In the present study, the effect of the addition of boron on the electrical conduction properties of nanocrystalline cerium oxide (CeO₂) was investigated. Pellets consisting of pure CeO₂ and a mixture of CeO₂ and 10 mol.% of boron oxide (B-CeO₂ samples) were sintered at 800 °C as well as 1100 °C and their electrical conduction properties investigated by impedance spectroscopy at different temperatures and oxygen partial pressures. The nanocrystalline B-CeO₂ samples exhibit a higher electronic grain boundary conductivity and higher activation energy compared to a pure CeO₂ sample (1.41 eV for B-CeO₂ vs. 1.21 eV for pure CeO₂). According to electron energy-loss spectroscopy analysis, (i) boron can be detected only at the grain boundaries and (ii) cerium cations are lightly reduced at the grain boundaries. The results are consistent with both the formation of a space charge layer with a positive space charge potential but also with conduction along a glassy cerium-boron-oxide phase.     

Solid electrolytes with oxygen ion conduction

Oxygen ion conductors constitute an important class of solid electrolytes and have been extensively studied from scientific and technological standpoint. Most of the oxygen ion conductors (eg. those based on ZrO₂, ThO₂, CeO₂ and Bi₂O₃) have a perfect or distorted fluorite type structure. Some oxides with a perovskite type structure also exhibit oxygen ion conduction. All these materials show enhanced conductivity when doped with aliovalent impurities. The defect structure of these materials and the resulting transport properties (electrical conductivity, diffusion and transference number) are discussed as a function of temperature, oxygen partial pressure and composition. Some of the important measurement methods are briefly surveyed. Interface phenomena receive attention as they affect transport behaviour at the electrode - electrolyte combination. Defect interactions in these massively defective solids are presented through an analysis of theoretical models. Finally, some of the important applications of the oxygen ion conductors in fuel cells, oxygen probes and pumps and electrochemical decomposition of water are indicated.     

Electrical properties of nanocrystalline Sm-doped ceria ceramics

Electrical properties of nanocrystalline materials are usually different than that of microcrystalline. This phenomenon is not fully understood and therefore it is of continuous interest in the scientific community. In this paper, the results of investigation of nanocrystalline Sm-doped ceria prepared by a net shape technology are presented. The net shape technology is a relatively new ceramic preparation method, which combine powder and polymer precursor methods. The ceramics prepared in this way can be dense and nanocrystalline. Net-shaped prepared Sm-doped ceria was fabricated in the form of bulk ceramics and film on platinum foil. Their electrical properties were investigated and compared with the results obtained from microcrystalline sample.     

Synthesis and silica coating of calcia-doped ceria/mica nanocomposite by seeded polymerization technique

Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of the excellent UV light absorption property and low catalytic ability for the oxidation of organic materials superior to undoped ceria. In order to reduce the oxidation catalytic activity further, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique. Generally, nanoparticles of inorganic materials do not provide a good coverage for human skin because of the agglomeration of the particles. The platy particles are required to enhance the covering ability of inorganic materials. This can be accomplished by synthesis of calcia-doped ceria/mica nanocomposite with subsequent silica coating to control catalytic activity of calcia-doped ceria. Calcia-doped ceria/mica nanocomposite was prepared by soft solution chemical method followed by silica coating via seeded polymerization technique. Silica coated calcia-doped ceria/mica nanocomposite was characterized by X-ray diffraction, SEM, TEM, XPS and FT-IR.     

Electrical properties of bulk and grain boundaries of scandia-stabilized zirconia co-doped with yttria and ceria

The electrical properties of bulk and grain boundaries of scandia-stabilized zirconia co-doped with yttria and ceria have been determined as a function of temperature (300 < T/°C < 700) and oxygen partial pressure [10^− 24 ≤ p(O₂)/bar ≤ 1, T = 700 °C] by application of impedance spectroscopy. The yttria and ceria contents of Ce_xY_0.2 − xSc_0.6Zr_3.2O_8 − δ (0 ≤ x ≤ 0.2) have been varied systematically. Homogeneous samples have been prepared by means of a sol-gel (glycine-nitrate) combustion process. The ionic conductivity in air is almost independent of composition with typical values around 0.03-0.04 S cm^− 1 for the bulk at 700 °C. A significant decrease of the ionic conductivities of bulk and grain boundaries is found for samples co-doped with ceria at low oxygen partial pressures [p(O₂) < 10^− 15 bar, T = 700 °C]. Activation energies for the ionic transport in oxidizing (air) and reducing (1%-H₂/Ar) atmospheres have been extracted from Arrhenius-plots. The oxygen nonstoichiometry in 1%-H₂/Ar has been investigated by employing thermogravimetry. The decrease of the ionic conductivity under reducing conditions is accompanied by an increase of the corresponding high temperature activation energy of the bulk, which is interpreted in terms of defect association or clustering.     

Electrical conduction and dielectric properties of vanadium phosphate glasses doped with lithium

AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, σ_ac=Aω^s. The obtained values of the power s lie in the range 0.5≤s≤1 for both undoped and doped with low lithium content which confirms the electron hopping between V⁴⁺ and V⁵⁺ ions. For doped glasses with high lithium content, the values of s≤0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V⁵⁺.     

Electrical conduction properties of rare earth orthophosphates under reducing conditions

Electrical conduction properties of Sr-doped PrPO₄, NdPO₄ and SmPO₄ with the monazite structure were investigated at 500–925 °C under H₂/H₂O reducing conditions. From H/D isotope effects and p(H₂)-dependencies of the conductivities, it was found that the materials dominantly conducted protons under the wet reducing conditions although the materials slightly showed n-type electronic conduction at higher temperatures. Based on p(H₂O) and p(H₂)-dependencies of the conductivities, defect structures of the materials under the reducing conditions were discussed. As a result, it was considered that major positive defects were oxygen deficits at higher temperatures and protons at lower temperatures.     

Electrical properties and conduction mechanism in the sodium nickel diphosphate

The Na_3.6Ni_2.2(P₂O₇)₂ compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction and vibrational and impedance spectroscopy. The AC electrical conductivity and the dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 kHz–1 MHz and 564–729 K, respectively. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The peak positions ω _m of M″ spectra shift toward higher frequencies with increase in temperature. The AC conductivity data fulfill the power law. Application of the correlated barrier hopping model revealed that the ionic conduction takes place by single-polaron and bipolaron hopping processes.     

Electrical conductivity and oxygen permeation properties of SrCoFeOx membranes

The total conductivity and oxygen permeation properties of dense SrCoFeO_x membranes synthesized from the solid state method were studied in the temperature range of 700–900 °C. The SrCoFeO_x membranes consist of an intergrowth (Sr₄Fe_6 − xCo_xO_13 ± δ), perovskite (SrFe_1 − xCo_xO_3 − δ), and spinel (Co_3 − xFe_xO₄) phase. SrCoFeO_x exhibits n-type and p-type conduction at low and high oxygen partial pressures, respectively, and has a total conductivity of 16.5 S/cm at 900 °C in air. The oxygen permeation fluxes for SrCoFeO_x and SrFeCo_0.5O_x membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeO_x membranes than SrFeCo_0.5O_x membranes and can be attributed to a difference in the amount and makeup of the perovskite phase present in each composition. The oxygen permeation fluxes with a carbon monoxide sweep gas were approximately two orders of magnitude larger than the fluxes measured with an inert sweep gas for both compositions. The large oxygen permeation fluxes observed with a carbon monoxide sweep are due to a higher driving force for oxygen transport and a reaction on the sweep side of the membrane that maintains a low oxygen partial pressure.     

Electrical conduction and thermodynamic properties of K2NiP2O7

The pyrophosphate K₂NiP₂O₇ has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state ³¹P magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state ³¹P MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at ?17.66 and ?19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz–1 MHz and 603–728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond–West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.     

Electrical conduction of emulsion explosives

Results of experiments to obtain a spatial distribution of electrical conduction of emulsion explosives for different content of a sensitizer are presented.     

Electrical and piezoresistive properties of ion beam deposited DLC films

In present study diamond like carbon (DLC) films were deposited by closed drift ion source from the acetylene gas. The electrical and piezoresistive properties of ion beam synthesized DLC films were investigated. Diode-like current–voltage characteristics were observed both for DLC/nSi and DLC/pSi heterostructures. This fact was explained by high density of the irradiation-induced defects at the DLC/Si interface. Ohmic conductivity was observed for DLC/nSi heterostructure and metal/DLC/metal structure at low electric fields. At higher electric fields forward current transport was explained by Schottky emission and Poole–Frenkel emission for the DLC/nSi heterostructures and by Schottky emission and/or space charge limited currents for the DLC/pSi heterostructures. Strong dependence of the diamond like carbon film resistivity on temperature has been observed. Variable range hopping current transport mechanism at low electric field was revealed. Diamond like carbon piezoresistive elements with a gauge factor in 12–19 range were fabricated.     

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷ Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25 eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3 × 10¹¹ to 3.8 × 10¹² ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25 eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.     

Electrical conduction in copper vanadate

A.C. and d.c. electrical conductivities, thermoelectric power and dielectric constant of copper vanadate (CuV₂O₆) have been measured in the temperature range 300–1000 K in order to discuss the electrical conduction in the compound. The extrinsic conduction, which takes place below 500 K, has been explained by small polaron hopping mechanism while intrinsic conduction, which takes place above 500 K, has been explained by large polaron band mechanism in view of the values of activation energy and charge carrier mobility in the temperature ranges 300–500 K and 500–1000 K.     

Quantum origin of the oxygen storage capability of ceria

The microscopic mechanism behind the extraordinary ability of ceria to store, release, and transport oxygen is explained on the basis of first-principles quantum mechanical simulations. The oxygen-vacancy formation energy in ceria is calculated for different local environments. The reversible CeO2-Ce2O3 reduction transition associated with oxygen-vacancy formation and migration is shown to be directly coupled with the quantum process of electron localization.     

Electrical conduction in manganese tungstate

The a.c. and d.c. electrical conductivity and thermoelectric power of a single crystal of MnWO₄ are reported in the temperature range 300–1200 K. It has been found that the dominant charge carriers are holes over the entire temperature range studied. A break in the log σ-($\text{1}\text{T}$) curve occurs around 600 K. The activation energies below and above this break temperature have been estimated as 0.53 and 0.57 eV. The charge carrier mobilities have also been estimated. The data have been analysed using the polaronic concept of electrical conduction.     

磷离子注入纳米金刚石薄膜的n型导电性能与微结构研究

系统研究了磷离子注入并在不同温度退火后的纳米金刚石薄膜的微结构和电学性能.研究表明,当退火温度达到800 ℃以上时,薄膜呈良好的n型电导.Raman光谱和电子顺磁共振谱的结果表明,薄膜中金刚石相含量越高和完整性越好,薄膜电阻率越低. 这说明纳米金刚石晶粒为薄膜提供了电导.1000 ℃退火后,薄膜晶界中的非晶石墨相有序度提高,碳悬键数量降低,薄膜电阻率升高.薄膜导电机理为磷离子注入的纳米金刚石晶粒提供了n型电导,非晶碳晶界为其电导提供了传输路径. 关键词： 纳米金刚石薄膜 n型 磷离子注入