Contactless conductivity of nanoparticles from electron magnetic resonance lineshape analysis

A contactless method to determine the electrical conductivity of nanoparticles is presented. It is based on the lineshape analysis of electron magnetic resonance signals which are ‘Dysonian’ for conducting samples of sizes larger than the skin depth. The method is validated by measurements on a bulk sample of La_0.67Sr_0.33MnO₃ where it gives values close to those obtained from direct measurement of conductivity and is then used to determine the conductivity of nanoparticles of La_0.67Sr_0.33MnO₃ dispersed in polyvinyl alcohol as a function of temperature.     

Investigation of film-thickness dependent thermal conductivity of Gd2Zr2O7 thin films

Gadolinium zirconium oxide (Gd₂Zr₂O₇) films, a promising candidate for thermal barrier coatings and buffer layers in superconductors, are deposited on Al₂O₃ substrate by using an RF-magnetron sputtering method for the study of thermal conductivity. Thermal conductivity is measured by both methods of time domain thermoreflectance and 3 omega methods, which can give rise to the difference in the heat penetration depth. Since phonon mean free path in Gd₂Zr₂O₇ is smaller than lattice constant due to oxygen vacancy, the film thickness variation in 100–500 nm does not affect thermal conductivity seriously unless interfacial thermal resistance is involved. The interfacial effect can be included or excluded in thermal conductivity depending on the heat penetration depth of heat waves. There is discrepancy between the experimental results of thermal conductivity obtained by the two methods, due to the effect of interfacial thermal resistance. The interfacial effect on thermal conductivity is verified through comparison of the two experimental results, and the Debye–Callaway modeling.     

Mixed ion effects in Na/Cu-NaZr2(PO4)3

The mixed ion effect by which the conductivity minimum of a crystal with three dimensional diffusion path is observed is firstly reported for Na/Cu-NaZr₂(PO₄)₃. The phase diagram is also obtained by estimating the frequency dependence of ionic conductivity. The behavior is in agreement with the conductivity result. NMR spectra (²³Na MAS) showed the formation of an ordered distribution among different kinds of ions. The ionic conductivity of the mixed ion system Na/Cu was calculated for a two dimensional honeycomb lattice by means of the path probability method (PPM). It suggested that the mixture of two ions led to the conductivity minimum. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Nanostructure,conductivity, and reflectivity of thin iron and (Fe) X (BaF2) Y films

Fe and (Fe) _X (BaF₂) _Y films 10- to 160-nm-thick are grown on a polymer substrate by vacuum evaporation. The surface relief and nanostructure of the films are examined. The dependence of the conductivity on the film thickness is obtained, and a correlation between the conductivity and surface relief is found. The influence of the BaF₂ dielectric phase on the conductivity and reflectivity of the Fe films is studied. It is shown that the BaF₂ layer to some extent slows down oxidation and maintains the reflectivity of the Fe films compared with pure iron films exposed to air.     

Influence of dispersed alumina particles on the transport characteristics of mechanochemically synthesized NaSn2F5

The composite solid electrolytes, NaSn₂F₅, dispersed with submicron size Al₂O₃ fillers of various concentrations and particle sizes have been synthesized through mechanochemical milling technique. X-ray diffraction and microstructure results indicate the biphasic nature of the composite materials. The transport properties of the present composite materials have been investigated by means of impedance spectroscopy, and the results show that the improvement in conductivity increases with decrease in the particle size of the filler. An enhancement in conductivity of two orders in magnitude is obtained for NaSn₂F₅ with Al₂O₃ dopant concentration of 10 mol%. The activation energy responsible for conductivity relaxation, calculated from the modulus spectra, is found to be almost the same as the value obtained from temperature variation of dc conductivity. The scaling result of the imaginary part of the modulus shows the temperature-independent relaxation behavior.     

Vitreous solid state electrolytes in the system of RNO3–Zn(NO3)2–KHSO4–P2O5

The structure and electric conductivity of glasses in the system RNO₃–Zn(NO₃)₂–KHSO₄–P₂O₅ (R = Na, K) obtained at different temperatures were investigated by IR and impedance spectroscopy. Glasses fused at 250–350 °C demonstrated an increase of their ionic conductivity in 10³ times in comparison with the same compositions fused at 550 °C. The influence of the chemical composition on the structure and properties of the obtained glasses was analyzed. It is proposed that the high ionic conductivity of glasses obtained at low temperatures is related to the incorporation of the nitrate ions between long (PO₃)_n chains, similar to the iodide ions; this resulted in a maximal coordination of the local conduction space for the cation associated with a disordered glass network.     

Electrical property of nanocrystalline γ-Fe2O3 under high pressure

Using a microcircuit fabricated on a diamond anvil cell, in situ conductivity measurements on nanophase (NP) γ-Fe₂O₃ are obtained under high pressure. For NP γ-Fe₂O₃, the abrupt increase in electrical conductivity occurs at a pressure of 21.3 GPa, corresponding to a transition from maghemite to hematite. Above 26.4 GPa, conductivity increases smoothly with increasing pressure. No distinct abnormal change is observed during decompression, indicating that transformation is irreversible. The temperature-dependence of the conductivity of NP γ-Fe₂O₃ was investigated at several pressures, indicating the electrical conductivity of the sample increases with increasing pressure and temperature, and that a remarkable phenomenon of discontinuity occurs at 400 K. The abnormal change is attributed to the electronic phase transitions of NP γ-Fe₂O₃ due to the variation of inherent cation vacancies. Besides, the temperature-dependence of the electrical conductivity displays semiconductor-like behavior before 33.0 GPa.     

Influence of Gd3+ and Dy3+ co-doping and sintering regime on enhancement of electrical conductivity of ceria-based solid electrolyte

In order to improve the conductivity of ceria-based solid electrolytes, effect of co-doped Gd³⁺ and Dy³⁺ was evaluated. For this purpose, nano-crystalline Gd_0.2???x Dy _x Ce_0.8O_1.9 powders with various composition ranges (x?=?0.05, 0.1, 0.15, 0.2) were initially synthesized by high-energy milling method. The effect of micro-structural evolution and co-doping on electrical properties of the dense sintered samples fabricated by two-step sintering and conventional sintering of the synthesized powders were investigated. Electrical conductivity of the samples was discussed based on the results obtained by AC impedance spectroscopy at temperatures in the range of 300–700 °C. The co-doping and sintering regime were found to significantly influence the conductivity of the electrolytes. The electrical conductivity of the co-doped samples depends on Dy³⁺ content and the maximum conductivity obtained by 0.15 mol% Dy and 0.05 mol% Gd. The conductivity of Gd_0.2???x Dy _x Ce_0.8O_1.9 (x?=?0.15) was 0.03 S/cm at 700 °C. A thorough discussion was made, based on the present experimental data.     

Conductivity of Wigner liquid

The conductivity of two-dimensional electron systems with low carrier concentration is considered on the basis of the previously suggested model (Fermi liquid with a soft mode) under the assumption that the equilibrium in each of the (fermion and boson) subsystems is established faster than the impurity relaxation and the relaxation between the subsystems (hydrodynamic approximation). The conductivity of the system depends on three characteristic times: τ₁(τ₂) is determined by the fermion (boson) impurity scattering and τ₁₂ is determined by the friction between the subsystems; the respective temperature dependences are obtained. The conductivity is related to the relaxation time τ in the usual way, and τ obeys the relationship τ^?1=τ ₁ ^?1 +(τ₂+τ₁₂)^?1. It follows from the results obtained that the resistivity of pure samples should increase with temperature and tend towards saturation.     

Optimised NASICON ceramics for Na+ sensing

NASICON dense ceramics were obtained from solid state reaction between SiO₂, Na₃PO₄·12H₂O and two different types of zirconia: monoclinic ZrO₂ and the yttria-doped tetragonal phase (ZrO₂)_0.97(Y₂O₃)_0.03. Higher temperatures were needed to obtain dense samples of the yttrium free composition (1265 °C). The electrical conductivity, at room temperature, of the yttria-doped samples sintered at 1230 °C (0.20 S/m) is significantly higher than the value obtained with the material prepared from pure ZrO₂. The impedance spectra show that the differences in conductivity are predominantly due to the higher grain boundary resistance of the undoped ceramics, probably due to formation of monoclinic zirconia and glassy phases along the grain boundary. Further improvement of the electrical conductivity could be achieved after optimization of the grain size and density of grain boundaries. A maximum conductivity value of about 0.27 S/m at room temperature was obtained with the yttria-doped samples sintered at 1220 °C for 40 h. Yttria-doped and undoped ceramics were tested as Na⁺ potentiometric sensors. The detection limit of the yttria-doped sample (10⁻⁴ mol/l) was one order of magnitude lower than the obtained with the undoped material. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Thermoelectric power of mixed electronic-ionic conductors II. Case of titanium dioxide

The purpose of the present work is the determination of the thermopower components corresponding to different charge carriers (electrons, electron holes and ions) for TiO₂ and the use of these data for evaluation of the effect of symmetry between these two properties. The procedure of the determination of these components was based on the following two approximations:

The first approximation is based on a symmetrical model assuming a consistency between thermopower and electrical conductivity within the n-p transition (minimum of electronic component of the electrical conductivity corresponds to zero value of the electronic component of thermopower).

The second approximation is based on the apparent asymmetry between thermopower and electrical conductivity within the n-p transition as determined from the first approximation.

The analysis, based on the data of the electronic components of thermopower and electrical conductivity for TiO₂ single crystal, results in the band gap (using the Jonker formalism). The determined band gap is equal to 2.77 eV and 2.57 eV at the first and the second approximations, respectively, while the band gap determined from the experimentally measured data is equal 3.35 eV. These values are consistent with the band gap determined from the data of electrical conductivity corresponding to the n-p transition point (E_g=3.16 eV) and for the data measured experimentally and those free of the ionic conductivity component (E_g=2.79 eV). The obtained results indicate that thermopower and electrical conductivity most likely exhibit the effect of symmetry.     

Influence of interlayer coupling and intra-layer Coulomb interaction on electronic transport in bilayer graphene

Calculations of renormalized perpendicular conductivity within Kubo formula employing single particle temperature dependent Green's function formalism for bilayer graphene has been attempted. On the basis of numerical analysis, perpendicular conductivity as a function of temperature, interlayer coupling, onsite Coulomb interaction and carrier concentration per site has been analyzed for both AA- and AB-stacked bilayer graphene. It is found that perpendicular conductivity increases with interlayer coupling and also with temperature at low temperatures while at higher temperatures, there is saturation in perpendicular conductivity. Influences of onsite Coulomb interaction and carrier concentration per site on perpendicular conductivity is just opposite to each other while onsite Coulomb energy suppresses the rate of increase of σ_⊥/σ_⊥0 with temperature, on the other hand increase in carrier density per site enhance this rate significantly. Finally, theoretically obtained results on temperature dependent perpendicular conductivity are viewed in terms of electronic transport data as well as recent theoretical works available in bilayer graphene.     

The vibrational contribution to the thermal conductivity of a polyatomic fluid

A simple analytical expression is proposed in this article to calculate the vibrational contribution to the thermal conductivity of a polyatomic fluid. The analytic expression was obtained based on the assumption that the self-diffusion process is the major mechanism in the transport of vibrational energy. The proposed expression is validated by comparing the thermal conductivity of CO₂ calculated by molecular dynamics (MD) simulations to experimental data over a wide range of temperature and pressure. It is also demonstrated that the proposed analytic expression greatly increases the accuracy of calculated thermal conductivity for CO₂ at the supercritical state.     

Comparative study of solid-state reaction and sol-gel process for synthesis of Zr-doped Li<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> solid electrolytes

We investigated the synergistic influences of synthesis methods (solid-state reaction vs. sol-gel process) and Zr⁴⁺ doping on the structure and ionic conductivity of perovskite-structured Li_0.5La_0.5TiO₃ (LLTO) solid electrolytes. The lithium-ion conductivity of Li_0.5La_0.5Ti_1???x Zr _x O₃ ceramic specimens was evaluated as a function of x value and compared carefully between those two synthesis methods. Regarding the conductivity, sol-gel process is better for the synthesis of LLTO than solid-state reaction. As a result, the highest grain conductivity is obtained in the sol-gel-derived pure LLTO sample with x?=?0, reaching 1.10?×?10^?3 S?·?cm^?1. Partial substitution of Zr⁴⁺ enlarges the LLTO’s grain aggregate size and increases the total superficial area of aggregates. Consequently, Zr⁴⁺ substitution not only affects the grain (bulk) conductivity, but more importantly, also improves the grain boundary conductivity and the total conductivity. The highest total conductivity is 5.84?×?10^?5 S?·?cm^?1 with x?=?0.04 by sol-gel process.     

Dc and ac electrical conductivity of bulk CdSexTe1−x (0x0.4)

Measurements of the dc and ac conductivity were made for polycrystalline CdSe_xTe_1−x (0x0.4) at various frequencies (0.1–100 kHz) and at various temperatures (293–413 K). The temperature dependence of the dc conductivity was measured in the temperature range (293–413 K). It was found that the obtained dc activation energy for the investigated compositions decrease with the increase of Se content. The ac conductivity is found to be frequency and temperature dependent and obeys the Aω^s law, where s decreases with the increase of temperature. The ac conductivity of these compositions are explained on the basis of the correlated barrier hopping model.     

Electrical and thermal studies in the commensurate incommensurate phase region of (NH4)2ZnCl4 single crystal

DC electrical conductivity for a virgin and poled annealed (NH₄)₂ZnCl₄b-axis single crystal shows a defect controlled property. A Schottky mechanism is a probable mechanism of conduction in regions of strong structural transitions. The rise of conductivity in the incommensurate and paraelectric phases is linked to an increase in discommensurations density. The activation energies (ΔE) in the three phases region were calculated. DTA measurements shows that the crystal is stable up to 200 °C and the phase transition temperatures were observed at 42, 94.8 and 137 °C. The effective activation energy (E_e) was obtained using Kissinger and Mahadevan equations. It was found to be equal to 0.49 eV. This correlates with the value obtained through DC conductivity.     

流体静高压下的锂离子导电性

本文改进实验方法,在0.0001—1.23GPa流体静高压下测量了整片非晶锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃(x=0.05;0.15)及其粉末压片的离子电导率及激活体积。发现粉末压片电导率峰值是由非晶微粒间的接触电导及非晶微粒体电导两者叠加;对整片非晶电导率的压力效应用离子迁移通道的物理图象给出初步的微观解释。此外,还观测到氧化铝组分减少使电导率的压力转变点明显降低;测量出不同温度热处理以及300℃等温热处理4—20h后离子电导率-压力曲线的变化规律,仍可归因于非晶态相分离及两种非晶相的先后晶化。 关键词：     

Poly (ethylene oxide) (PEO)-based,sodium ion-conducting‚ solid polymer electrolyte films,dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> filler,for applications in sodium ion cells

The studies on solid polymer electrolyte (SPE) films with high ionic conductivity suitable for the realization of all solid-state Na-ion cells? form the focal theme of the work presented in this paper. The SPE films are obtained by the solution casting technique using the blend solution of poly (ethylene oxide) (PEO) with ethylene carbonate (EC) and propylene carbonate (PC) and complexed with sodium nitrate. Structural and thermal studies of SPE films are done by XRD, FTIR spectroscopy, and TGA techniques. Surface morphology of the films is studied using the FESEM. The ionic conductivity of SPE films is determined from the electrochemical impedance spectroscopy studies. For the SPE film with 16 wt% of NaNO₃ used for reacting with the polymer blend of PEO with EC and PC, the ionic conductivity obtained is around 1.08 × 10^?5 S cm^?1. Addition of the Al₂O₃ as the filler material is found to enhance the ionic conductivity of the SPE films. The studies on the Al₂O₃ modified SPE film show an ionic conductivity of 1.86 × 10^–4 S cm^?1, which is one order higher than that of the SPE films without the filler content. For the SPE film dispersed with 8 wt% of Al₂O₃, the total ion transport number observed is around 0.9895, which is quite impressive from the perspective of the applications in electrochemical energy storage devices. From the cyclic voltammetry studies, a wide electrochemical stability window up to 4 V is observed, which further emphasizes the commendable electrochemical behavior of these SPE films.     

Enhanced electrical transport in LiBrLiI mixed crystals and LiBrAl2O3 composites

LiBrLiI mixed crystals and LiBrAl₂O₃ composites have been studied by means of complex impedance analysis an conductivity, X-ray diffraction, DTA and SEM techniques. The substitution of wrong size I⁻ ions in LiBr increases the conductivity and decreases the migration energy of Li-ion vacancies. These results are consistent with those of the KBr-KI system and earlier predictions. LiBrAl₂O₃ composites exhibit a sharp increase in the conductivity. The highest conductivity obtained was ≈10⁻³ Ω⁻¹ cm⁻¹ at 302°C for LiBr + 10 m/o Al₂O₃.