Conductivity Isotherms Research Articles

Impedance spectroscopy of Bi-rich BiFeO3: Twin thermal-activations

Transport measurements data are presented on bismuth-rich BiFeO3 ceramic, synthesized by a solid state method. Conductivity isotherms were analyzed using Jonscher’s empirical power-law frequency dependence. Monotonically increasing frequency-exponent n(T) over 413–593 K indicates a small polaron tunnelling mechanism for the charge transport. Distinct linear regimes observed in the Arrhenius σdc vs. T−1 plot suggest that two different charge-carriers/conductivity-relaxations prevail above and below ∼490 K. Twin Arrhenius regimes of ac-conductivity also exhibit a sharp “transition” at 510 K, from the pinned-dipole/hopping-anion dynamics to the free-dipole/oscillating-ions response at higher temperatures. Furthermore, a concurrent behavior-change of the locus traced out by the charge-hopping frequency ωh [with σ(ωh) = 2σdc] also designates 510 K as delineating two different transport characteristics in the adjacent temperature regimes.

Fast Na ion transport triggered by rapid ion exchange on local length scales

The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of non-flammable ceramic electrolytes with very high conductivities. Na3Zr2(SiO4)2PO4-type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the µm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in Na3.4Sc0.4Zr1.6(SiO4)2PO4 that is characterized by an unprecedentedly high self-diffusion coefficient of 9 × 10−12 m2s−1 at −10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τNMR of only 2 ns. The underlying asymmetric diffusion-induced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely rapid Na+ jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.

PROPERTIES OF 1-BUTYL-3-METHYLIMIDAZOLIUM BROMIDE IONIC LIQUID AND ITS BLENDS WITH WATER AND BROMIDES OF SILVER, COPPER AND TANTALUM

Ionic liquids with N,N¢-dialkylimidazolium cation characterized now as "green" solvents are investigated intensively to find their practical application. In this research the physical-chemical, electrochemical and corrosion properties of 1-butyl-3-methylimidazolium bromide (BMImBr) and its blends with water and bromides of silver (I), cupper (II) and tantalum (V) were studied. BMImBr is a hygroscopic ionic liquid and in depending on a water content can exists as a solid, liquid, metastable supercooled melt, and two-phase system – liquid and crystalline hydrate of BМImBr´0.5Н2О composition. At 1:1 components ratio the structural transformation of the melt (СН2О<50 mol%) « the solution (СН2О>50 мол.%) was observed. The BMImBr ionic liquid is a good solvent towards bromides of silver (I), cupper (II) and tantalum (V). These salts destroy the inter- and intramolecular interactions of BMImBr and generate the complex metal-containing ions with Br- anion of ionic liquid. As a result the glass temperature and the density increased, the melting point decreased and on isotherms of dynamic viscosity and specific electro conductivity a distinct minimum was observed at the low concentration range of the salt. Electrochemical window of BMImBr is 1.9 V and it is limited by bromide ions oxidation in the anodic potential range and by imidazolium cations reduction in the cathodic potential range. Additions of the water and the metals salt are an electrochemical active. In their presence the redox processes proceeds inside of the electrochemical window and the discharge-ionization process is the limiting steps. From IL studied the thin films of silver and copper can be deposited with good adhesion on metal substrates including tantalum and titanium. Investigated ionic liquids are a corrosive fluid, and corrosion of the metal increases dramatically in the presence of the same cations.

Ionic-to-Electronic Conductivity Crossover in CdTe-AgI-As2Te3 Glasses: An 110mAg Tracer Diffusion Study.

Conductivity isotherms of (CdTe) x(AgI)0.5- x/2(As2Te3)0.5- x/2 glasses (0.0 ≤ x ≤ 0.15) reveal a nonmonotonic behavior with increasing CdTe content reminiscent of mixed cation effect in oxide and chalcogenide glasses. Nevertheless, the apparent similarity appears to be partly incorrect. Using 110mAg tracer diffusion measurements, we show that semiconducting CdTe additions produce a dual effect: (i) decreasing the Ag+ ion transport by a factor of ≈200 with a simultaneous increase of the diffusion activation energy and (ii) increasing the electronic conductivity by 1.5 orders of magnitude. Consequently, the conductivity minimum at x = 0.05 reflects an ionic-to-electronic transport crossover; the silver-ion transport number decreases by 3 orders of magnitude with increasing x.

Stabilization effects on the thermal conductivity and sorption behavior of earth bricks

The renaissance of earth building is mainly motivated by the thermal and hygric properties of the material. These earthen materials qualities lead to improve the hygrothermal conditions in indoor environment. Today, stabilization of earth bricks by addition of chemical stabilizers is a common approach used to maintain and improve its use for construction. Although the addition of cementitious stabilizing agents enhances the engineering properties of soil, it is not the case for their hygrothermal properties. In this work, an experimental investigation is performed on stabilizers effects on thermal conductivity and moisture sorption isotherms of compressed earth bricks. Four water vapor sorption models are evaluated by fitting the sorption isotherms data of un-stabilized and stabilized compressed earth bricks. Soil blocks have been manufacturing with locally material. They are stabilized with cement or lime contents of 5%, 8%, 10% and 12%.The results show that the thermal conductivity increases as a function of stabilizers contents. The measuredsorption data of earth bricks showed that stabilization induces a reduction of material water vapor permeability. It’s found that Henderson model is the best for fitting sorption isotherms data over the studied range of relative humidity.

Fast Na Ion Transport Triggered By Rapid Ion Exchange on Local Length Scales

The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of nonflammable ceramic electrolytes with very high conductivities. Na3Zr2(SiO4)2PO4-type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the μm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in Na3.4Sc0.4Zr1.6(SiO4)2PO4 that is characterized by an unprecedentedly high self-diffusion coefficient of 9 ' 10−12 m2s−1 at –10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τNMR of only 2 ns. The underlying asymmetric diffusion- induced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely fast Na jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.

Hygrothermal properties of bio-insulation building materials based on bamboo fibers and bio-glues

This study focuses on manufacturing by thermo-pressing new low-environmental-impact bio-insulation fiberboards from bamboo fibers and bone glue, modified with sodium lignosulfonate. The aims are to measure moisture buffer value, water vapor permeability, bending properties, thermal conductivity and vapor sorption isotherms of these materials. The moisture buffer values of these materials belong to the “excellent” category, ranging from 2.5 to 3.9g/(m2.%RH), higher than the value for bamboo fiberboard without glue (1.7g/(m2.%RH). The water vapor diffusion resistance factor ranges from 8 to 17, which is similar with other fiber insulation materials. The bending properties show a significant improvement when 30% (w/w) glue is used, the glue being a mixture between bone and sodium lignosulfonate glues. Moreover, the variation in thermal conductivity of the fiberboards with relative humidity and moisture content is investigated to evaluate the hygrothermal performance of the fiberboards. The results are promising for both thermal insulation and moisture buffering, thus these fiberboards could be used for passive control of indoor environment.

Influence of modifier on dielectric and ferroelectric properties of aluminosilicate glasses

Glasses with compositions SiO2-CaO-Al2O3-TiO2-Na2O were prepared by conventional melt quench technique. The dielectric properties of these glasses with a variation in alkali content over a frequency range from 20Hz to 1MHz and temperature variation of 30–280°C have been investigated. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The present glasses exhibit conductivity in the range of 10−5 to 10−3S/m which is higher than the alkali containing silicate glasses. Hysteresis loop observed at room temperature confirms the ferroelectric nature of glasses.

Determination of oxygen nonstoichiometry in SrFeO3−δ by solid‐state Coulometric titration

AbstractThe oxygen nonstoichiometry of SrFeO3−δ was determined by solid‐state Coulometric titration at 750°C‐1040°C and 10−18≤pO2(atm)≤0.5. At T≤850°C, a hysteresis in the oxygen nonstoichiometry (δ) isotherms indicates the presence of a two‐phase region corresponding to a mixture of a perovskite and an oxygen vacancy ordered phase. The variation of δ with temperature at fixed pO2 values and the variation of log(pO2) with reciprocal temperature at fixed δ are reported. The pO2 at the p‐n transition in the electrical conductivity increases as the temperature increases, and the transition in the conductivity isotherm occurs at a composition of SrFeO2.505(1) at 950°C and SrFeO2.508(1) at 900°C. Since strontium exclusively occupies the A‐site, a simple point defect model that assumes noninteracting defects can describe the isotherms but only at 1040°C; nonideal behavior is observed at lower temperatures. The partial molar thermodynamic quantities for oxygen in SrFeO3−δ were determined.

Electrical and complex dielectric behaviour of composite polymer electrolyte based on PEO, alumina and tetrapropylammonium iodide

In this study, the electrical, dielectric and morphological analysis of composite solid polymer electrolytes containing polyethylene oxide, alumina nano-fillers and tetrapropylammonium iodide are conducted. The temperature dependence of conductivity shows activation energy of 0.23, 0.20 and 0.29 eV for electrolytes containing 0, 5 and 15 wt.% alumina, respectively, when data fitted to the Arrhenius equation. These activation energy values are in good agreement with those determined from dielectric measurements. The result confirms the fact that conductivity is activated by both the mobility and the charge carrier density. The conductivity isotherms demonstrated the existence of two peaks, at 5 and 15 wt.% Al2O3 composition. The highest conductivity values of 2.4 × 10−4, 3.3 × 10−4 and 4.2 × 10−4 S cm−1 are obtained for the sample with 5 wt.% Al2O3 at 0, 12 and 24 °C, respectively, suggesting an enhancement of conductivity compared with that of alumina free samples.

Na+ ion conducting glasses in the NaCl-Ga2S3-GeS2 system: A critical percolation regime

Sodium chalcogenide and chalcohalide glasses exhibit high ionic conductivity and can be used in all-solid-state batteries, chemical sensors and other devices. However, the available information on NaCl-containing chalcogenide glass systems is relatively poor. In this work we will present conductivity results for (NaCl)x(Ga2S3)0.2–0.2x(GeS2)0.8–0.8x glasses over a wide composition range, changing between x=10−4 and 0.3, i.e., 3.5 orders of magnitude. Dc conductivity and ac impedance measurements have been used to study the electric properties of this glassy system. The room temperature conductivity increases by 11 orders of magnitude with increasing sodium concentration, ranging between 10−17Scm−1 (x=0) and 10−6Scm−1 (x=0.3, y=10.1at.% Na). The activation energy decreases from 0.99 to 0.35eV, respectively. The composition dependence of the ionic conductivity shows two drastically different transport regimes at low (x≤0.1, y≤3.1at.% Na) and high (x>0.1) sodium concentrations. A characteristic feature of the conductivity isotherm for diluted glasses is a power law dependence of the ionic conductivity σi(y)∝yT0/T, where T0 is the critical temperature related to connectivity of the host glass. The rapid increase of conductivity in a rather limited concentration range and the power law dependence of σi(y) are thus caused by a percolation-controlled mechanism. Deviations from the critical percolation regime are observed at higher sodium content and presumably related to the change in the ion transport mechanism.

Electric properties of carbon nano-onion/polyaniline composites: a combined electric modulus and ac conductivity study

The complex electric modulus and the ac conductivity of carbon nano-onion/polyaniline composites were studied from 1 mHz to 1 MHz at isothermal conditions ranging from 15 K to room temperature. The temperature dependence of the electric modulus and the dc conductivity analyses indicate a couple of hopping mechanisms. The distinction between thermally activated processes and the determination of cross-over temperature were achieved by exploring the temperature dependence of the fractional exponent of the dispersive ac conductivity and the bifurcation of the scaled ac conductivity isotherms. The results are analyzed by combining the granular metal model (inter-grain charge tunneling of extended electron states located within mesoscopic highly conducting polyaniline grains) and a 3D Mott variable range hopping model (phonon assisted tunneling within the carbon nano-onions and clusters).

Organic Vs. Inorganic Cations of Alkali-Metal Halides Containing Ionic Liquids for Sodium-Ion Battery Applications

The power generation from either fossil fuels or preferably renewable energy sources is on the rise throughout the world. The pursuit of electrochemical devices for energy storage during peak power grid utilization is viable. There is great interest in further developing sodium batteries, particularly ZEBRA-type cells with chloroaluminate electrolytes. This lab has worked on understanding of weak-field, low-melting metal-halide based ionic liquids for use in the sodium-ion conducting batteries at a low-temperature of operation. This undertaking employed both organic and inorganic cations of low charge density, including the much-studied dialkylimidazolium cation. The vital issue of decreased ionic conductivity caused by alkali ion-trapping in these electrolytes long known as a qualitative effect was recently quantified, discussed, and reported by us. We have since compared the conductivities of binary bromoaluminates in which large inorganic cations PBr4 + formed by a bromide transfer process were used to replace the former dialkylimidazolium cation and here show the differences in the figure below. Currently, the electrochemical (along with other physical) properties are being characterized in preparations for testing in ZEBRA-type cells. This study leads to improved understanding of the factors determining electrolyte and electrochemical performance of sodium-containing binary electrolytes over a range of temperatures. Figure: The top set of three conductivity isotherms are for [EMIM]AlCl4 - NaAlCl4 solutions, and the bottom set of three are for PBr4Al2Br7 - NaAl2Br7 solutions of varying molar fractions. The completely inorganic electrolyte requires 100oC (top blue line isotherm) to attain the ionic conductivity of the electrolyte containing the organic cation at 60oC (mid black line isotherm). We attribute the difference to incomplete bromide transfer in the formation of the large inorganic cation of the second system. The “alkali cation-trapping” effect probably remains in effect. Figure 1

AC Conduction and Time-Temperature Superposition Scaling in a Reduced Graphene Oxide-Zinc Sulfide Nanocomposite.

We report, herein, the results of an in depth study and concomitant analysis of the AC conduction [σ'(ω): f=20 Hz to 2 MHz] mechanism in a reduced graphene oxide-zinc sulfide (RGO-ZnS) composite. The magnitude of the real part of the complex impedance decreases with increase in both frequency and temperature, whereas the imaginary part shows an asymptotic maximum that shifts to higher frequencies with increasing temperature. On the other hand, the conductivity isotherm reveals a frequency-independent conductivity at lower frequencies subsequent to a dispersive conductivity at higher frequencies, which follows a power law [σ'(ω)∝ω(s) ] within a temperature range of 297 to 393 K. Temperature-independent frequency exponent 's' indicates the occurrence of phonon-assisted simple quantum tunnelling of electrons between the defects present in RGO. Finally, this sample follows the "time-temperature superposition principle", as confirmed from the universal scaling of conductivity isotherms. These outcomes not only pave the way for increasing our elemental understanding of the transport mechanism in the RGO system, but will also motivate the investigation of the transport mechanism in other order-disorder systems.

Commensurate Phases of Kr Adsorbed on Single-Walled Carbon Nanotubes

In this paper, we show that Krypton atoms form a commensurate solid (CS) phase with a fractional coverage of one krypton atom per every four carbons on zigzag carbon nanotubes. This is a unique phase, different from the $$\sqrt{3} \times \sqrt{3}$$ R30 $$^\circ $$ CS monolayer formed on graphite, which has a lower coverage of one krypton atom per every six carbons. Our prediction disagrees with experiments that observe in nanotubes the same solid structure found on graphite. In order to address this discrepancy, we simulated adsorption of Kr on zigzag and armchair single-walled carbon nanotubes with radii ranging from 4.7 to 28.83 A. Our simulations confirm that the CS of coverage 1/4 forms on medium-sized zigzag nanotubes. We also found the 1/6-coverage solid on graphene, which represents the infinite-radius limit of a nanotube. Our findings are key to experiments of adsorption on nanotubes where the interpretation and justification of the results are based on the monolayer coverage, such as mass or conductance isotherms measurements.

The ionic transport mechanism and coupling between the ion conduction and segmental relaxation processes of PEO20-LiCF3SO3 based ion conducting polymer clay composites.

A series of ion conducting polymer-clay composites has been prepared using a solution casting technique. Relaxation dynamics and the ionic transport mechanism are systematically studied employing broadband dielectric spectroscopy over a wide frequency and temperature range. Among different phenomenological and theoretical models for ion conduction in disordered ionic conductors, conductivity isotherm spectra are analysed using the modified Almond-West and random free energy barrier model. Conductivity scaling suggests that the ionic transport mechanism is independent of temperature, and a similar inference is also obtained using scaled electrical modulus spectra. DC conductivity along with conductivity and segmental relaxation time following the Vogel-Tammann-Fulcher relationship suggests coupling between the ionic transport and segmental relaxation processes. Electrical modulus and dielectric formalism are used to understand the conductivity and segmental relaxation processes, respectively. The presence of first and second universality in the ionic transport mechanism is discussed using the real part of conductivity spectra and dielectric loss spectra. The crossover between the first and second universality is explained using the Kramer-Krönig approach. The ion diffusion coefficient is investigated using Ratner's classical approach in combination with the modified Stokes-Einstein relationship to correlate the coupled nature of the ion conduction mechanism and polymer segmental motion.

Thermal, Moisture and Biological Behaviour of Natural Insulating Materials

Besides having positive impact on sustainable development, natural building materials also have technical properties comparable with standard materials and important additional qualities. This article focuses on thermal, moisture and biological properties of thermal insulating materials based on vegetal and animal fibres.There is a lack of data regarding natural building materials and furthermore the properties of these types of materials can be site-dependent. Therefore the natural insulating materials have been tested for thermal, moisture and biological properties. In the research array, there were following materials: treated sheep wool, raw sheep wool, wood fibre, hemp, flax, straw bale and compressed straw panel. The main examined parameters are the thermal capacity, thermal conductivity, volume density and sorption isotherm, which are stated and compared. In addition to that, the microbiological identification tests were made together with the mould growth observation.The results of all tests and measurements are stated and discussed in the article with the emphasis on the situation in the real building stock where the test bordering conditions possibly occur

Electrical conductivity of molten ZnCl2–BeCl2 mixtures

The electrical conductivity of ZnCl2–BeCl2 molten mixtures has been measured for the first time. The measurements are performed over a wide temperature range including supercooling regions. Isotherms of the electrical conductivity of ZnCl2–BeCl2 are found to demonstrate negative deviations from additive magnitudes.

Organic Vs. Inorganic Cations of Alkali-Metal Halide Containing Ionic Liquids for Sodium-Ion Battery Applications

The power generation from either fossil fuels or preferably renewable energy sources is on the rise throughout the world. The pursuit of electrochemical devices for energy storage during peak power grid utilization is viable. There is great interest in further developing sodium batteries, particularly ZEBRA-type cells with chloroaluminate electrolytes. This lab has worked on understanding of weak-field, low-melting metal-halide based ionic liquids for use in the sodium-ion conducting batteries at a low-temperature of operation. This undertaking employed both organic and inorganic cations of low charge density, including the much-studied dialkylimidazolium cation. The vital issue of decreased ionic conductivity caused by alkali ion-trapping in these electrolytes, long known as a qualitative effect was recently quantified, discussed, and reported by us. We have since compared the conductivities of binary bromoaluminates in which large inorganic cations PBr4 + formed by a bromide transfer process were used to replace the former dialkylimidazolium cation and here show the differences in the figure below. Currently, the electrochemical (along with other physical) properties are being characterized in preparations for testing in ZEBRA-type cells. This study leads to improved understanding of the factors determining electrolyte and electrochemical performance of sodium-containing binary electrolytes over a range of temperatures. Figure: The top set of three conductivity isotherms are for [EMIM]AlCl4 - NaAlCl4 solutions, and the bottom set of three are for PBr4Al2Br7 - NaAl2Br7 solutions of varying molar fractions. The completely inorganic electrolyte requires 100oC (top blue line isotherm) to attain the ionic conductivity of the electrolyte containing the organic cation at 60oC (mid black line isotherm). We attribute the difference to incomplete bromide transfer in the formation of the large inorganic cation of the second system. The “alkali cation-trapping” effect probably remains in effect. Figure 1

Phase Equilibria and Ionic Solvation in the Lithium Tetrafluoroborate–Dimethylsulfoxide System

The phase diagram and electrical conductivity isotherms for the lithium tetrafluoroborate (LiBF4)–dimethylsulfoxide (DMSO) system and Raman spectra of DMSO and the LiBF4–DMSO solution were studied. Spectroscopic signatures of a H-bond between DMSO and BF4 − ions were found. The bonds of Li+ ions to the solvent were stronger than the bonds in DMSO dimers because formation of the solvate destroyed dimeric DMSO molecules. The τω values for DMSO molecules in the Li+-ion solvate shell of the LiBF4–DMSO system were similar to those for associated solvent molecules.