Activation Energy For Ionic Conduction Research Articles

Oxide ion transport in undoped and Cr-doped LaCoO 3− δ

The results of chemical and self-diffusion coefficient of oxygen vacancies, oxygen ionic conductivity and ionic transport numbers measured as a function of oxygen partial pressure p O 2 and temperature in the ranges − 4 ≤ log( p O 2 , atm) ≤ 0 and 900 ≤ T, °C ≤ 1050, respectively, are presented for the perovskite-type undoped LaCoO 3− δ and doped with chromium LaCo 0.7Cr 0.3O 3− δ cobaltites. The dependencies of these properties on oxygen partial pressures were shown to have monotonic character. This can, therefore, indicate that defect clusters or associates containing oxygen vacancies do not form in the oxides over complete p O 2 range investigated. The predominant charge carriers in both undoped and Cr-doped lanthanum cobaltite are electron defects, since oxygen vacancies transport numbers do not exceed 2 · 10 −3 %. The substitution of Cr for Co was found to lead to decrease of both ionic conductivity and oxygen chemical diffusion coefficient. Activation energy of ionic conductivity of the oxides studied decreases with the oxygen nonstoichiometry increase. Self-diffusion coefficient of oxygen vacancies and their mobility were shown to be independent of oxygen partial pressure and nonstoichiometry most likely due to lack of the defects interaction in the oxide studied.

Effect of divalent dopants on crystal structure and electrical properties of LaAlO 3 perovskite

Oxide ion solid electrolytes are materials which exhibit high oxide ion conductivity. In this study, inexpensive perovskite-type oxide, LaAlO 3 was doped with various types of divalent cations. The objective was to investigate the effect of dopants on the crystal structure and conductivity of LaAlO 3. As a result, the solubility of Ca ion into the La cation sublattice was found to be 5 mol% and the solubility of Sr ion could reach 20 mol%. However, only less than 1 mol% Ba ion could be dissolved. In this study, Mg ion was substituted for Al ion in the B-site. The solubility of Mg ion was about 3 mol%. With double doping for A and B parent cations, the addition of Ca, Sr, Ba ion tend to enhance the solubility of Mg ion from 3 to 10 mol%. Although the addition of Mg ion increased the solubility of Ca ion, the solubility of Sr and Ba ion was suppressed. The concentration of oxygen vacancy increases with the increasing amount of divalent cation dopants, within their solubility limits. However, the second phases were found to be stoichiometric compounds without oxygen defects. Thus, the conductivity of second phases was significantly lowered. In the LaAlO 3 perovskite systems, the activation energies for ionic conduction were also significantly influenced by the addition of dopants. The activation energy for singly and doubly doped samples, were about 89–108 and 90–126 kJ/mol, respectively, which is lower than that for undoped LaAlO 3 (∼127 kJ/mol).

Sintering of Ce 0.8Sm 0.2O 1.9

Ce 0.8Sm 0.2O 1.9 (SDC) powder was prepared with an oxalate coprecipitation route. SDC solid solutions were sintered at various temperatures ranging from 1100 ∼ 1450 °C, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, and electrical conductivity measurements. The optimized processing parameters for densification were to uniaxially press the sample at 200 ∼ 400 MPa and sinter it at 1350 ∼ 1400 °C for 4 h. The density of the sintered pellets was > 90% of the theoretical density; their soakage was <0.5%; and the average grain size was 1 ∼ 2 μm. The conductivities of the typical sintered specimen were 0.0133 and 0.0211 S ˙ cm −1 at 550 and 600 °C, respectively; Its activation energy for ionic conductivity was 0.62 eV. The dense SDC bulk material could be used as the electrolyte layer of low temperature solid oxide fuel cells.

Grain size effect on diffusion processes in superionic phases Cu1.75Se, Li0.25 Cu1.75Se, and Li0.25 Cu1.75S

Ionic conduction and chemical diffusion in Cu1.75Se, Li0.25 Cu1.75Se, and Li0.25Cu1.75S at 140–240°C are studied. The ionic conduction of Cu1.75 Se is shown to increase with the average grain size. With coarsening of grains, the activation energy for ionic conduction decreases in Cu1.75Se and increases in Li0.25Cu1.75S. The reasons for the diffusion effects observed in the studied materials are discussed.

Ionic conduction and chemical diffusion in solid solutions of superionic conductors Cu2X-Me2X (Me = Ag, Li; X = S, Se)

Ionic conduction and chemical diffusion in silver-and lithium-substituted superionic copper selenides and sulfides are studied. Upon substitution of lithium for copper, a strong increase in the activation energy of ionic conduction in copper sulfide and selenide and the concomitant several-fold decrease in the ionic conductivity are observed. The reasons for the deterioration of ionic transport conditions are elucidated. In contrast to the substitution of lithium for copper, the substitution of silver leads to higher ionic conductivity and the appearance of superionic conduction by two types of cations. Structural aspects of diffusion are considered. Different consequences of substitution of atoms into the cationic sublattice are associated with different electronic sheaths of lithium (alkali metal), silver, and copper (noble metals), which give rise to different types and degrees of hybridization of valence electrons of atoms in the disordered sublattice and the anionic frame.

Ionic conduction and effect of cation doping in Tl4HgI6

The ionic conduction properties of undoped and doped Tl4HgI6 were investigated using electrical conductivity, dielectrics, differential scanning calorimetry, and X-ray diffraction techniques. The heavy Tl+-ions diffusion was activated at high temperature, whereas low conductivity at the lower temperature suggested electronic contribution in undoped Tl4HgI6. The partial replacement of heavy Tl+ ion by suitable cations (Ag+ and Cu+) enhanced the conductivity by several orders of magnitude, whereas diminution in conductivity results with increasing dopants’ concentration in Tl4HgI6. These results can be interpreted in terms of a lattice contraction and vacancy–vacancy interaction (leading to the cluster formation), respectively. The dielectric values of undoped Tl4HgI6 system gradually increasing with temperature, followed by a sharp change, were observed around 385 K and can be explained on the basis of increasing number of space charge polarization and ions jump orientation effects. The activation energy of undoped and doped Tl4HgI6 systems were calculated, and it was found that ionic conductivity activation energy for 5 mol% of cation dopants is much lower than that of undoped one, and also 10 mol% doped Tl4HgI6 systems.

The ionic Seebeck effect and heat of cation transfer in Cu2−δSe superionic conductors

The ionic Seebeck coefficients of Cu2−δSe superionic conductors are measured in the temperature range 340–380°C. The data obtained are used to determine the heat of transfer Q i of copper ions as a function of the degree of nonstoichiometry and the temperature. The heat of transfer of copper cations increases from 0.19 to 0.22 eV as the degree of nonstoichiometry δ increases from 0.015 to 0.050. It is noted that the heat of transfer Q i tends to increase with an increase in the temperature. Assumptions regarding the specific features of the cation diffusion in the Cu2−δSe superionic conductors are made from the observed closeness of the heat of transfer and the activation energy for ionic conduction.

Soret effect and heat of silver atom transport in Ag(2 − x) + δCuxSe (x = 0.1, 0.2, 0.4) superionic solid solutions

Thermal-gradient-driven steady-state transport of silver atoms in Ag(2−x)+δCuxSe (x = 0.1, 0.2, 0.4) alloys is studied. The composition gradient along a sample in a thermal gradient is determined to be dδ/dT = (0.2–0.6) tx 10−5 K−1. The heart of ionic transport far exceeds the heat of electronic transport and is close to the activation energy of ionic conductivity.

Ion Transport in the Microporous Titanosilicate ETS-10

Impedance spectroscopy was used to investigate ion transport in the microporous crystalline framework titanosilicate ETS-10 in the frequency range from 1 Hz to 10 MHz. These data were compared to measured data from the microporous aluminosilicate zeolite X. Na-ETS-10 was found to have a lower activation energy for ion conduction than that of NaX, 58.5 kJ/mol compared to 66.8 kJ/mol. However, the dc conductivity and ion hopping rate for Na-ETS-10 were also lower than NaX. This was found to be due to the smaller entropy contribution in Na-ETS-10 because of its high cation site occupancy. This was verified by ion exchanging Na(+) with Cu(2+) in both microporous frameworks. This exchange decreases the cation site occupancy and reduces correlation effects. The exchanged Cu-ETS-10 was found to have both lower activation energy and higher ionic conductivity than CuX. Zeolite X has the highest ion conductivity among the zeolites, and thus the data shown here indicate that ETS-10 has more facile transport of higher valence cations which may be important for ion-exchange, environmental remediation of radionucleotides, and nanofabrication.

Highly Efficient Electron Stimulated Desorption of O+ from Gadolinia-Doped Ceria Surfaces

Highly efficient electron stimulated desorption of O+ from gadolinia-doped ceria (GDC) surfaces annealed at 850 K in ultrahigh vacuum is observed and investigated. O+ desorption has a major threshold of approximately 40 eV and an intrinsic kinetic energy of approximately 5.6 eV. Since the threshold energy is close to Ce 5s and Gd 5s core levels, Auger decay of core holes is likely associated with O+ desorption from sites related to oxygen vacancies. The interactions of water and molecular oxygen with GDC surfaces result in a decrease in O+ desorption, suggesting that water and oxygen molecules adsorb mainly to oxygen vacancies. The dependence of O+ kinetic energies on the incident electron energy and temperature reveals surface charging as a result of electron trapping, hole trapping, and electron-hole recombination. The activation energy for surface charge dissipation is found to be 0.43 eV, close to the activation energy for ionic conduction (0.47 to 0.6 eV) in the same material.

Anhydrous Proton-Conducting Polymeric Electrolytes for Fuel Cells

The need to design proton-conducting electrolytes for fuel cells operating at temperatures of 120 degrees C and above has prompted the investigation of various "water-free" polymeric materials. The present study investigates the properties of "water-free" proton-conducting membranes prepared from high-molecular-weight polymeric organic amine salts. Specifically, the properties of bisulfates and dihydrogenphosphates of poly-2-vinylpyridine (P2VP), poly-4-vinylpyridine (P4VP), and polyvinylimidazoline (PVI) have been investigated over the temperature range of 25-180 degrees C. Nanocomposites of these polymeric organic amine salts and hydroxylated silica have also been investigated in this study. These polymers are found to be stable and proton-conducting at temperatures up to 200 degrees C. In all the polymer examples studied herein, the phosphates are more conducting than the bisulfates. The activation energy for ionic conduction was found to decrease with increasing temperature, and this is associated with the increased polymer mobility and ionization of the proton. This is confirmed by the high degree of motional narrowing that is observed in proton NMR experiments. The measured values of conductivity and the differences in pKa values of the polymeric organic amine and the mineral acid are clearly correlated. This observation provides the basis for the design of other water-free acid-base polymer systems with enhanced proton conductivity. The results presented here suggest that anhydrous polymer systems based on acid-base polymer salts could be combined with short-range proton conductors such as nanoparticulate silica to achieve acceptable conductivity over the entire temperature range.

Lithium Ion Conductivity of Polymer Electrolytes Based on Insoluble Lithium Tetrakis(pentafluorobenzenethiolato)borate and Poly(ethylene oxide)

Lithium ion conductivity and the ion transport mechanism for heterogeneous polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato)borate (LiTPSB), which has weak interaction between the lithium ion and the counteranion, and high molecular weight poly(ethylene oxide) (PEO) have been investigated. In addition, the ionic conductivity of polymer electrolytes based on low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME) or amorphous poly[tetra(ethylene glycol) methyl ether methacrylate] (PEGM) was also researched. LiTPSB is not soluble in any solvents and polymers, however its composites with poly(ether)s exhibited ionic conductivity. The lithium ion transport mechanism in the interfacial phase between LiTPSB and PEO was proposed. The apparent activation energy of ionic conductivity was smaller for LiTPSB/PEO (salt ) than lithium trifluoromethanesulfonate (Litrif)/PEO. A high lithium ion transference number of 0.65–0.75 was also obtained for the insoluble LiTPSB/PEO system. A new peak of the melting point of PEO was observed in differential scanning calorimetry measurements of LiTPSB/PEO polymer electrolytes, and it suggested the formation of a new ion conducting phase in the interfacial region between LiTPSB and PEO.

Lithium ion conductive polymer electrolyte by side group rotation

Ionic conductive materials are of much interest as an electrolyte for solid-state lithium batteries. Poly(alkylene oxide) and lithium salt complex exhibits high ionic conductivity in terms of its high solubility for lithium salts. However, the temperature dependency of its ionic conductivity is quite large and non-linear, the ionic conductivity drops down at low temperature, especially below glass transition temperature of the polymer. Because its ionic conductive mechanism is derived from its segmental motion of polymer main chain. A novel ionic conductive material, poly[2,6-dimethoxy- N-(4-vinylphenyl)benzamide] is synthesized and confirm ionic conductivity even below glass transition temperature. Ionic conductivity of the polymer with lithium ditrifluoromethylsulfonate imide complex shows 10 −5 S cm −1 from 0 to 60 °C. Its temperature dependency is linear, namely Arrehnius type dependency. Evaluating from these data, activation energy of ionic conductivity for temperature region from 20 to 60 °C is calculated as 31 kJ mol −1 and that for temperature region from −20 to 20 °C is 11 kJ mol −1. Judging from these results, we conclude that the ionic conductivity of the polymer salt complex derived from 2,6-dimethoxyphenyl group rotation, instead of segmental motion of the polymer.

Electrical properties and crystallization processes in AgI–Ag 2O–P 2O 5, [Ag 2O]/[P 2O 5] = 3, glasses

The effect of crystallization processes in the xAgI·0.75(100 − x)Ag 2O·0.25(100 − x)P 2O 5, 50 ≤ x ≤ 75, glasses on the ionic conductivity was investigated, using impedance spectroscopy, X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The crystallization was induced and promoted by thermal processing. It was found out that depending on annealing conditions, the conductivity could be enhanced or lowered. The conductivity enhancement is observed when the glass is annealed near the glass transition temperature T g for relatively short time. In this case, the XRD patterns do no indicate the presence of crystalline phases. The decrease of conductivity is observed for more pronounced crystallization, detectable by X-ray diffraction. The annealing does not affect the activation energy of ionic conductivity.

Mechanochemical synthesis of nonstoichiometric fluorite Ca1−x LaxF2+x nanocrystals from CaF2 and LaF3 single crystals

The nonstoichiometric Ca{sub 1-x} La{sub x}F{sub 2+x} phase (x {>=} 0.1) is obtained by mechanochemical synthesis from CaF{sub 2} and LaF{sub 3} single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the MF{sub m}-RF{sub n} systems (m < n {<=} 4). The average grain size ranges within 10-30 nm. The temperature dependence of ionic conductivity of the mechanochemically synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200-250 deg. C) coincides with the conductivity of the single crystals of the same composition (Ca{sub 0.8}La{sub 0.2}F{sub 2.2}). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.

Synthesis and characterization of niobium phosphate glasses containing barium and potassium

The structural characteristics of phosphate glasses containing different amounts of Nb were investigated by X-ray diffraction, thermal analysis, Raman, and infrared spectroscopy. Phosphate glasses can be produced with relatively high amount of niobium by increasing the cooling rate without crystallization. Niobium is a glass former, is located in octahedral sites, and replaces tetrahedral phosphate groups by P, Nb, and O linked mixed chains. The density increases from 3.32g/cm3 to 3.73g/cm3, the elastic modulus increases from 56GPa to 78GPa, and the linear thermal expansion coefficient decreases from 24.7×10−6°C−1 to 7.9×10−6°C−1 as the amount of Nb increases. The glass transition temperature (Tg) increases from 480°C to 653°C as the amount of Nb increases from 5 to 37mol% because the Nb–O–P and Nb–O–Nb linkages are stronger than the O–P bond, requiring higher temperatures for relaxation. Electrical measurements showed that the activation energy for ionic conduction increases from 0.46eV to 0.59eV for glasses containing 19–32mol% of Nb2O5.

Atomistic simulations of oxide ion diffusion in heavily doped lanthanum cobaltite

Molecular dynamics simulations of perovskite-structured LaCoO 3 doped with alkaline earth and transition metal elements have been performed to provide a theoretical assessment of the relationship between oxide ion conductivity and composition in this system. Conductivities for compositions La 1− x Sr x Co 1− y Fe y O 3− δ (0.8 < x < 0.9, 0 < y < 1.0) at 1500 °C are reported. Several compositions are simulated at other temperatures in order to estimate the activation energies for ionic conductivity. Conductivity is found to increase with increasing strontium content, but exhibits a minimum for iron contents of 50% irrespective of the strontium content. Although substitution of Co 2+ ions for Co 3+ ions increases the volume fraction of oxide ion vacancies, the ionic conductivity decreases as a result of strong interactions between the lower valency dopants and vacancies.

Ionic conductivity of a poly(vinylpyridinium)/silver iodide solid polymer electrolyte system

A series of quaternized poly(2-vinylpyridine) (PVP) polymers has been synthesized with the general formula [(PVP) R]I, where R=H, Me, Bu. Addition of AgI to the polymers results in new silver ion conducting solid polymer materials. Conductivities as high as 6×10 −3 S/cm have been observed for the 3:1 AgI/[(PVP)Me]I composition. Analogous materials with a 3:1 composition for the protonated and butyl-substituted polymers display lower conductivities near 2×10 −4 S/cm. Conductivity studies, as a function of temperature, show these materials to be thermodynamically stable with a low activation energy for ion conduction. Differential scanning calorimetry experiments suggest that a new phase with the general formula (PVP) RAg 3I 4 forms with silver ions in a new amorphous state.

Comparison of dissolution behavior and ionic conduction between Sr and/or Mg doped LaGaO3 and LaAlO3

Abstract The dissolution of divalent cations plays an important role in the enhancement of conductivity for perovskite-based LaAlO 3 and LaGaO 3 oxygen conductors. In the LaAlO 3 system, the solubility of MgO was less than 10% due to the mismatch of ionic radius between the Mg and Al cations. The substitution of Sr ions in the La-cation sublattice was as high as 20%. With the doubly-doping of SrO and MgO in LaAlO 3 , the enhancement of MgO solubility was also observed. However, further addition of MgO tends to lower the solubility of Sr ion from 20 to 10%. This result can be rationalized by the reduced distance between Mg ion and Sr ion that caused the cation–cation repulsion in the perovskite structure. In the singly-doped LaGaO 3 systems, the solubility of MgO was found to be 20%. However, only less than 10% of the La-cation sublattice could be substituted by Sr ions. With the doubly-doping of SrO and MgO, the solubility of SrO was significantly enhanced by the addition of MgO. It is believed that the solubility enhancement of SrO is due to the expanded lattice caused by the addition of MgO. Within the solubility limit of the aliovalent cations, the ionic conductivities of both LaAlO 3 and LaGaO 3 systems increased with the increasing concentration of foreign cations. After the solubility limits in both doped LaAlO 3 and LaGaO 3 were reached, the segregation of the second phase tends to lower the ionic conductivity drastically. The activation energy for ionic conduction was also dependent on the ionic radius of foreign cations which may affect the space available for the transport of oxygen ions.

Transport properties and Mössbauer spectra of Fe-substituted La 10− x(Si,Al) 6O 26 apatites

Increasing iron content in apatite-type La 9.83Si 4.5Al 1.5− y Fe y O 26+ δ ( y=0.5–1.5) leads to increasing unit cell volume, fraction of Fe 4+, partial oxygen ionic and p-type electronic conductivities, and ceramics sinterability. The oxygen ion transference numbers, determined by Faradaic efficiency (FE) measurements at 973–1223 K in air, are in the range 0.986–0.994. Data on total conductivity and Seebeck coefficient as functions of the oxygen partial pressure, varying in the range 10 −2 Pa to 70 kPa, confirm that under oxidizing conditions the ionic conduction in Fe-substituted La 9.83(Si,Al) 6O 26+ δ apatites is dominant. Due to stabilization of Fe 3+, substantially worse transport properties are observed for A-site stoichiometric La 10Si 4Fe 2O 26, having activation energy for ionic conductivity of 107 kJ/mol and electron transference numbers close to 0.03. The correlation between partial ionic and electron-hole conductivities suggests a significant role of Fe 4+ formation compensated by extra oxygen incorporation into the vacant sites, which are formed due to Frenkel-type disorder induced by La vacancies. The average thermal expansion coefficients of Fe-doped La 10− x (Si,Al) 6O 26+ δ ceramics, calculated from dilatometric data in air, are 8.9×10 −6 to 9.9×10 −6 K −1 at 300–1250 K.