Ionic and electronic conduction of oxygen ion conductors in the Bi2O3−Y2O3 system

The ionic conduction of sintered samples of Bi₂O₃?Y₂O₃ containing 20–30 mol% Y₂O₃ has been investigated by means of ac conductivity experiments and EMF measurement of an oxygen concentration cell using the specimen tablet as electrolyte. Ac conductivity was measured at a frequency of 10 kHz under oxygen partial pressures ranging from 1 to 10^-21 atm. The results show that these materials possess high ionic conduction. The conductivities for samples containing 22.5–30 mol% Y₂O₃ are many times higher than those of stabilized zirconia-based solid electrolyte at corresponding temperatures. The ratio of E_meas./E_calc. of an oxygen concentration cell Pt∣O₂(air)∣Bi₂O₃?Y₂O₃∣O₂(pure oxygen)∣Pt is close to 1 which shows that the materials containing 22.5 to 30 mol% Y₂O₃ are nearly pure ionic conductors. The p-type conductivity is negligible at higher P_O2 values. The n-type conduction for a sample containing 27.5 mol% Y₂O₃ was investigated using the Coulomb titration technique in which the following cell was used: Pt Rh∣O₂(air)∣Bi₂O₃?Y₂O₃∣[O]_sn∣W.log P_é=-767000/T+665. P_é is equal to 2.6×10^-61 atm at 800°C. The n-type conductivity is also very small. Thus these materials are good oxygen ionic conductors.     

Diffusion of 55Fe in Fe2O3 single crystals

The diffusion of ⁵⁵Fe has been measured parallel to the c axis of Fe₂O₃ single crystals at temperatures in the range 708–1303°C and at an oxygen activity of unity. The tracer penetration profiles were determined using sectioning techniques. For temperatures above 900°C the tracer diffusion coefficient is given byD¹(Fe) = 1.6 × 10⁹ exp[?6.0 (eV)/kT] cm² s^?1 and below 900°C by 2.8 × 10^?9 exp[?1.8 (eV)kT]. The high-temperature behaviour is probably characteristic of pure Fe₂O₃, whereas diffusion at lower temperatures may be influenced by impurities. The most likely defects responsible for diffusion of Fe are iron interstitials and, for oxygen, oxygen vacancies, and the observed activation energies are discussed in terms of the properties of these defects. The diffusion data and defect models have been used to predict the rate of growth of Fe₂O₃ and indicate that outward Fe diffusion is the dominant transport process. Previously published data for Fe₂O₃ growth in a variety of experimental situations have been corrected to a single rate constant using a model for multilayer growth. The corrected data are all in good agreement but are approximately two orders of magnitude greater than predicted from diffusion data, which suggests that grain boundary diffusion controls the growth of Fe₂O₃ in practice.     

Novel layered perovskite GdBaCuFeO5+x as a potential cathode for proton-conducting solid oxide fuel cells

A layered perovskite GdBaCuFeO_5+x (GBCuF) was developed as a cathode material for intermediate-temperature solid oxide fuel cells based on a proton-conducting electrolyte of stable BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY). The X-ray diffraction results showed that GBCuF was chemically compatible with BZCY after co-fired at 1,000 °C for 10 h. The thermal expansion coefficient of GBCuF, which showed a reasonably reduced value (15.1?×?10^?6 K^?1), was much closer to that of BZCY than the cobalt-containing conductor. The button cells of Ni–BZCY/BZCY/GBCuF were fabricated and tested from 500 to 700 °C with humidified H₂ (～3 % H₂O) as a fuel and ambient oxygen as the oxidant. A high open-circuit potential of 1.04 V, maximum power density of 414 mW cm^?2, and a low electrode polarization resistance of 0.21 Ω cm² were achieved at 700 °C, with calculated activation energy (E _a) of 128 kJ mol^?1 for the GBCuF cathode. The experimental results indicated that the layered perovskite GBCuF is a good candidate for cathode material.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

Electrochemical properties of intermediate-temperature SOFCs based on proton conducting Sm-doped BaCeO3 electrolyte thin film

Dense BaCe_0.8Sm_0.2O_2.90 (BCSO) thin films were successfully fabricated on porous NiO–BCSO substrates by dry pressing process. As characterized by scanning electron microscope, the BCSO films were about 50 μm. With Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) as cathodes, single cells were tested at 600 and 700 °C with humidified (3% HB₂O) hydrogen as fuel and oxygen as oxidant. The open circuit voltage of 1.049 V at 600 °C and 1.032 V at 700 °C were achieved, indicating negligible gas permeation through the BCSO thin films. Maximum power densities of 132 and 340 mW/cm² were obtained at 600 and 700 °C, respectively. The impedance measurements at open circuit conditions showed that there were two rate-limiting processes for the electrode reactions and that the cell performances were essentially determined by the electrode polarization resistances at temperature below 650 °C, which implied that it was essential to reduce the electrode polarization by developing novel electrode materials to improve the performance of ITSOFC based on BCSO electrolyte. Conductivities of BCSO under the cell operating circumstances were obtained as 0.00416, 0.00662 and 0.00938 Scm^− 1 at 500, 600 and 700 °C, respectively. The activation energy of BCSO conductivity was calculated as 29.5 and 43.8 kJ/mol for the temperature range of 550–700 °C and of 400–550 °C, respectively. Endurance test was firstly carried out with 75 μm BCSO electrolyte at 650 °C at the operating voltage of 0.7 V and current density about 0.12 A/cm². Both voltage and current density remained stable for 1000 min.     

PVA-assisted synthesis and characterization of nano-crystalline La3+ and Mg2+ co-doped CeO2 electrolyte for intermediate-temperature solid oxide fuel cells

A series of nano-crystalline ceria-based solid solution electrolyte, Ce_0.8La_0.2?x Mg_xO_2?δ (x?=?0.0, 0.05, 0.10, 0.15, and 0.2), were synthesized via the polyvinyl alcohol (PVA) assisted combustion method, and then characterized to the crystalline structure, powder morphology, sintering micro-structure, and electrical properties. Present study showed that Ce_0.8La_0.2?x Mg _x O_2?δ was exceedingly stable as a cubic phase in all temperature range and exhibited fine crystals ranging from 15 to 20 nm. After sintering at 1,400 °C, the as-prepared pellets exhibited a dense micro-structure with 96 % of theoretical density. The electrical conductivity was studied using AC impedance spectroscopy and it was observed that the composition Ce_0.8La_0.1?Mg_0.1O_2?δ showed higher electrical conductivity of 0.020 S?cm^?1 at 700 °C. The thermal expansion was measured using dilatometer technique in the temperature range 30–1,000 °C. The average thermal expansion coefficient of Ce_0.8La_0.1?Mg_0.1O_2?δ was 12.37?×?10^?6 K^?1, which was higher than that of the commonly used SOFC electrolyte YSZ (~10.8?×?10^?6 K^?1).     

A preliminary study on a new LiBOB/acetamide solid phase transition electrolyte

New solid electrolytes containing acetamide and lithium bioxalato borate (LiBOB) with different molar ratios have been investigated. Their melting points (T_m) are around 42 °C. The ionic conductivities and activation energies vary drastically below and above T_m, indicating a typical feature of phase transition electrolyte. The ionic conductivity of the LiBOB/acetamide electrolyte with a molar ratio of 1:8 is 5 × 10^? 8 S cm^? 1 at 25 °C but increases to 4 × 10^? 3 S cm^? 1 at 60 °C. It was found that anode materials, such as graphite and Li₄Ti₅O₁₂, could not discharge and charge properly in this electrolyte at 60 °C due to the difficulty in forming a stable passivating layer on the anodes. However, a Li/LiFePO₄ cell with this electrolyte can be charged properly after heating to 60 °C, but cannot be charged at room temperature. Although the LiBOB/acetamide electrolytes are not suitable for Li-ion batteries due to poor electrode compatibility, the current results indicate that a solid electrolyte with a slightly higher phase transition temperature than room temperature may find potential application in stationary battery for energy storage where the electrolyte is at high conductive liquid state at elevated temperature and low conductive solid state at low temperature. The interaction between acetamide and LiBOB in the electrolyte is also studied by Raman and FTIR spectroscopy.     

Electrical conductivity of the system Y2O3CeO2

The electrical conductivity of the system Y₂O₃CeO₂ was measured in the temperature range 500–1100°C and P_o2 range 10^–7?10^?1 atm. Possible defect models were suggested on the basis of conductivity data, which were investigated as a function of temperature and of P_o2. The observed activation energies were 0.40 eV and 1.79 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on P_o2 were in the temperature range 500–750°C and at temperatures from 750–1100°C. It is suggested that the system Y₂O₃CeO₂ shows a mixed ionic plus hole conduction due to an O^″_i defect and an electronic hole conduction due to a V^'''_Y defect in the low- and high-temperature regions, respectively.     

Synthesis and electric properties of perovskite Pr0.6Ca0.4Fe0.8Co0.2O3 for SOFC applications

In this study, polycrystalline powder Pr_0.6Ca_0.4Fe_0.8Co_0.2O₃ (PCFC) was synthesized by a sol–gel process. This oxide was analyzed by X-ray powder diffraction. Synthesized Pr_0.6Ca_0.4Fe_0.8Co_0.2O₃ showed up to be single phase and belongs to the orthorhombic crystalline system with a Pbnm space group. The microstructural features of the synthesized products display particles having an irregular morphology and a size in the range of 50–100 nm. X-ray diffraction (XRD) analysis shows the chemical compatibility between the PCFC cathode and the electrolyte Sm-doped ceria since no reaction products were honored when the material was mixed and co-fired at 1,000 °C for 168 h. The thermal expansion coefficient of PCFC 16.9?×?10^?6 °C^?1 is slightly higher than that of Ce_0.8Sm_0.2O_1.9 (SDC) over the studied temperature range. The greater contribution to the total resistance of the electrode is the electrochemical resistance associated with oxygen exchange in the cathode surface (0.96 Ωcm²). The dc four-probe measurement indicated that PCFC exhibits fairly high electrical conductivity, over 100 S cm^?1 at T?≥?500 °C, making this material promising as a cathode material for intermediate temperature solid oxide fuel cells.     

Conductivity of β″ and ion rich β alumina.I.H.+(H2O)n compounds

The conductivity and thermal stability of H⁺(H₂O)_n β″ and ion rich β alumina single crystals have been measured by the complex impedance method in the 25–700°C temperature range. Two mechanisms of conductivity were assumed: proton transfer at lower temperatures and H₃O⁺ diffusion in the high-temperature range. Both structures have similar properties, but ion rich β alumina possesses the best stability and the lowest activation energy (β: 0.15 eV, β″: 0.20 eV below 400 and 300°C respectively). The room-temperature conductivity is ≈5×10^?6 Ω^?1 cm^?1. The conducting properties and mechanisms are discussed and compared to other protonic or ionic conductors.     

Ionic conductivity of Zr1−xIn2xO2−x

As x in Zr(In)O_2?x is increased from 0.08 to 0.16 (9–19 mole per cent In₂O₃) the activation energy E(x) for ionic conduction increases from 1.05 to 1.51 eV; the concuctivity decreases from 2 × 10^?5 to 3 × 10^?6Ω^?1cm^?1at 400°C, is composition-independent at about 580°C, and increases from 1 × 10^?2 to 4 × 10^?2Ω^?1cm^?1 at 800°C. The pre-exponential term of the Boltzmann-type conductivity equation depends exponentially on E(x), a much stronger dependence on x than theoretically expected with a model for ionic conductivity that includes nearest-neighbor defect interactions. Analysis of reported conductivity data for Zr(M)O_2?x (M = Sc, Y, Ca and rare earth metals) and other doped oxide electrolytes with fluorite-type structure reveals that the same relationship is observed with these materials when x γ0.08. It is shown that ionic conduction in these oxides is consistent with nearest neighbor vacancy-cation defect interaction forx < 0.08 but that an additional complex interaction with composition-dependent free energy ΔG(x) occurs when xγ 0.08.The lattice constant of Zr(In)O_2?x with the cubic fluorite-type structure is independent of composition, 5.114 ± 0.002 Å, in agreement with ionic size considerations.     

Thermoelectric power of (Me4N)2Ag13I15 and (Et4N)2Ag13I15

Thermoelectric power using reversible silver electrodes and electrical conductivity on the compressed pellets of (Me₄N)₂Ag₁₃I₁₅, and (Et₄N)₂Ag₁₃I₁₅ have been measured between room temperature and below 160°C. The results of θ can be expressed by the equations:?θ = 0.115 (10³/T)+0.2905VK^?1 and ?θ = 0.150 (10³/T) + 0.305mV K^?1; and those of conductivity by the equations; σ = 28.7 exp (?0.17eV/kT) ohm^?1cm^?1 and $\text{σ = 216.6 exp (?0.24e}\text{V}\text{kT}\text{)}$ ohm^?1cm^?1; respectively for Me- and Et-electrolytes. The results are discussed and compared with those of previous authors.     

Lithium aluminum nitride,Li3AlN2 as a lithium solid electrolyte

Single phase of Li₃AlN₂ was prepared from the mixture of Li₃N/AlN = 1.2 to 1.5 in molar ratio at 700°C and at 900°C. It crystalizes in the cubic system derived from antifluorite-type structure having the lattice parameter $\text{a = 9.470}\text{A}\text{?}$. It is a pure ionic conductor having conductivity of 5 × 10^?8ω^?1cm^?1 at room temperature and an activation energy of 52 kJ/ mol. Its decomposition voltage was 0.85 V at 104°C. The TiS₂/Li₃AlN₂/Li cell could be discharged at a constant current of 45 μA/cm² at 104°C.     

Covalent distribution of spin in V2O3:O17 nuclear resonance

O¹⁷ nuclear magnetic resonance has been observed in metallic V₂O₃ with frequency shifts from (?0.10 ± 0.02)-(?0.05 ± 0.02) per cent between 170 and 460°K respectively, a linewidth of 37 ± 5 oe and spin-lattice relaxation rate 1/T₁ ≈ 60 sec^?1 at 296°K. From these quantities, covalency parameters f_s/2S = ? 0.35 × 10^?3 and ?_π/2S ≈ ? 0.07 are calculated. One of the two vanadium 3d electrons in the antiferromagnetic state below the 170°K metal-insulator transition is inferred to lie in a non-magnetic state, while covalent charge transfer augments the spin moment of the other 3d electron to the observed 1.2 μ_B.     

Effect of Fe2O3 nanoparticles on combustion of coal surrogate (Anisole): Enhanced ignition and formation of persistent free radicals

This contribution explores the effect of nanoparticles of iron (III) oxide (Fe₂O₃) on the combustion of coal surrogate, i.e., anisole, identifying the changes in ignition features as well as the occurrence of persistent organic pollutants in the initiation channels. The method applies packed-bed reactor coupled with Fourier transform infrared (FTIR) spectroscopy to quantitate the ignition temperature under typical fuel-rich conditions, in-situ electron paramagnetic resonance (EPR) to elucidate the formation of environmentally-persistent free radicals (EPFR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor the chemisorption of organic substrates on the nanoparticles, as well as X-ray diffraction for particles characterisation (PXRD). We employ cluster-based quantum mechanical calculation to map the reaction pathway within the scope of the density functional theory. The results of Fe₂O₃-mediated combustion of anisole depict an excessive reduction in ignition temperature from 500?°C around 220?°C at λ?=?0.8. As confirmed both from EPR and DRIFTS measurements, the chemisorption of anisole on α-Fe₂O₃ surfaces follows the direct dissociation of the O–CH₃ (and OCH₂–H), leading to the formation of surface-bound phenoxy radicals at temperatures as low as 25?°C and incurring an estimated energy barrier of E_a?=?18?kJ mol^?1 and a preexponential factor of A?=?2.7?×?10¹² M^?1 s^?1. This insight applies to free-radical chain reactions that induce spontaneous fires of coal, as coal comprises ferric oxide nanoparticles, and equally to coexistence of aromatic fuels with thermodynamically reactive Fe₂O₃ surface, e.g., in fly ash, at the cooled-down tail of combustion stacks.     

Microstructure and electrochemical properties of porous La2NiO4+δ electrodes spin-coated on Ce0.8Sm0.2O1.9 electrolyte

Porous La₂NiO_4+?? electrodes were prepared from superfine starting powder on dense substrates of Ce_0.8Sm_0.2O_1.9 electrolyte by a spin coating technique. The microstructure and electrochemical properties of the electrodes were investigated within the sintering temperature range of 1,000?C1,100?°C. An obvious effect of sintering temperature on the microstructure and electrochemical properties was detected. The variation of the electrochemical properties with sintering temperature was explained in relation to the microstructural evolution of the porous electrodes. It was detected that the electrode processes greatly depended on the microstructure of the electrodes. The polarization of surface oxygen exchange process was found to be the major contribution to the total electrode polarization. The electrode sintered at 1,050?°C showed the optimum electrocatalytic activity among the investigated electrodes. At 800?°C, the electrode exhibited a polarization resistance of 0.42????cm², an overpotential of 48?mV at a current density of 200?mA?cm^?2 and an exchange current density of 121?mA?cm^?2.     

Evaluation of a cobalt-free Ba0.5Sr0.5Fe0.9Nb0.1O3?δ cathode material for intermediate-temperature solid oxide fuel cells

A cobalt-free Ba_0.5Sr_0.5Fe_0.9Nb_0.1O_3??? (BSFNb) perovskite-type oxide was investigated as the cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. XRD results showed that BSFNb cathode was chemically compatible with the electrolyte SDC up to 1,000?°C. The maximum output of anode-supported thin-film SOFC reached 503?mW?cm^?2 at 650?°C when employing humidified H₂ as fuel and static air as oxidizer. The electrode polarization resistance was low as 0.078????cm² at 650?°C, and the activation energy of the electrode polarization resistance was 129.72?kJ?mol^?1. The experimental results indicated that the cobalt-free BSFNb was a promising cathode candidate for IT-SOFCs.     

Raman scattering of high-temperature phase transition in KH2PO4

Raman scattering was applied to study the high-temperature phase transition (near 175°C) in KH₂PO₄. Drastic temperature-dependent changes were observed to take place in the normal modes of B₁ symmetry between 1000–3400 cm^?1. The disintegration of the dominant broad feature near 2500 cm^?1 when temperature rises beyond 150°C suggests that the alteration of the hydrogen-bond network is closely connected with this high-temperature phase transition.     

Polymer electrolytes based on polycarbonates and their electrochemical and thermal properties

Polycarbonates (4a–d) with various side chain lengths were synthesized by the reaction of 1,4-bis(hydroxyethoxy)benzene derivatives and triphosgene in the presence of pyridine. The polymer electrolytes composed of 4a–d with lithium bis(trifluoromethanesulfonyl)imide (LiN(SO₂CF₃)₂, LiTFSI) were prepared, and their ionic conductivities and thermal and electrochemical properties were investigated. 4d-Based polymer electrolyte showed the highest ionic conductivity values of 1.0?×?10^?4?S/cm at 80 °C and 1.5?×?10^?6?S/cm at 30 °C, respectively, at the [LiTFSI]/[repeating unit] ratio of 1/2. Ionic conductivities of these polycarbonate-based polymer electrolytes showed the tendency of increase with increasing the chain length of oxyethylene moieties as side chains, suggestive of increased steric hindrance by side chains. Unique properties were observed for the 4a(n?=?0)-based polymer electrolyte without an oxyethylene moiety. All of polycarbonate-based polymer electrolytes showed good electrochemical and thermal stabilities as polymer electrolytes for battery application.     

Cation self-diffusion and impurity diffusion in Fe2O3+

Cation self-diffusion D¹_Fe, parallel to the c axis has been measured as a function of temperature (1100–1300°C) and oxygen partial pressure p_o2 (2 × 10^?3-1 atm) in the same single crystals of Fe₂O₃ as those used by Chang and Wagner. Whereas the p_o2 dependence of D1_Fe, observed by Chang and Wagner has been confirmed, the absolute value of D¹_Fe and the activation enthalpy for self-diffusion are much higher than those reported by them. The various diffusion studies indicate that cation self-diffusion occurs by an interstitial-type mechanism. However, the sample-to-sample variations in D¹_Fe, suggest that all diffusion measurements may have been performed on samples where the defect concentrations are impurity controlled. Impurity diffusion of ⁶⁰Co, ⁵¹Cr, and ⁸⁸Y has also been measured as a function of p_o2 at 1200°C. The results indicate that these impurities diffuse by an interstitialcy mechanism in Fe₂O₃.