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The atomic mass ratio of ca. 2 between deuterium and hydrogen is the highest for any pair of stable isotopes and results in significant and measurable H/D isotope effects in high temperature proton conductors containing these species. This paper discusses H/D isotope effects manifested in O-H/O-D vibration frequencies, the mobility of H+/D+ carriers, the kinetics of the electrochemical oxidation of H2/D2, the solubilities of H2O/D2O and, finally, the spontaneous electromotive force that appears across H2/D2 cells with proton conducting electrolytes. Comparable work on tritium-exchanged materials is also discussed. The results highlight the usefulness of isotope effects in the study of high temperature proton conductors.

Microbial fuel cells (MFCs) can be used for electricity generation via bioconversion of wastewater and organic waste substrates. MFCs also hold potential for production of certain chemicals, such as H2 and H2O2. The studies of electricity generation in MFCs have mainly focused on the microbial community formation, substrate effect on the anode reaction, and the cathode's catalytic properties. To improve the performance of MFCs, the initiation process requires more investigation because of its significant effect on the anodic biofilm formation. This review explores the factors which affect the initiation process, including inoculum, substrate, and reactor configuration. The key messages are that optimal performance of MFCs for electricity production requires (1) understanding of the electrogenic bacterial biofilm formation, (2) proper substrates at the initiation stage, (3) focus on operational conditions affecting initial biofilm formation, and (4) attention to the reactor configuration.

The high temperature properties of Rb2SeO4 have been studied by calorimetry, impedance spectroscopy and X-ray powder diffraction. As synthesized, Rb2SeO4 includes a second phase of Rb2SeO3, which can be eliminated upon heating the compound. As expected, no conductivity is observed in dry (pH2O < 0.001 bar) air. By changing to humidified (pH2O = 0.1 bar) air at 176 °C, the conductivity increases sharply from 8.6·10−8 to 1.7·10−6 S cm−1. Under humidified (pH2O = 0.1 bar) reducing atmosphere (9%H2 in N2), the conductivity increases to 2.0·10−4 S cm−1 at 317 °C. Degradation of Rb2SeO3 and Rb2SeO4 to form RbOH, which is known as a proton conductor, are thought to be responsible for the observed conductivity in humidified atmospheres. Our observations may explain the conductivity rise in other solid acid electrolytes, including sulfate and selenate groups, around their decomposition temperatures, in humidified atmospheres.

Electricity production from microbial fuel cells fueled with hydrolysate produced by hydrothermal treatment of wheat straw can achieve both energy production and domestic wastewater purification. The hydrolysate contained mainly xylan, carboxylic acids, and phenolic compounds. Power generation and substrate utilization from the hydrolysate was compared with the ones obtained by defined synthetic substrates. The power density increased from 47 mW m −2 to 148 mW m −2 with the hydrolysate:wastewater ratio (R HW in m 3 m −3 ) increasing from 0 to 0.06 (corresponding to 0–0.7 g dm −3 of carbohydrates). The power density with the hydrolysate was higher than the one with only xylan (120 mW m −2 ) and carboxylic acids as fuel. The higher power density can be caused by the presence of phenolic compounds in the hydrolysates, which could mediate electron transport. Electricity generation with the hydrolysate resulted in 95% degradation of the xylan and glucan. The study demonstrates that lignocellulosic hydrolysate can be used for co-treatment with domestic wastewater for power generation in microbial fuel cells.

We report on the structural, magnetic and magnetocaloric properties of the Ni50Mn38Sb12Bx alloys in term of boron addition with x = 1, 3 and 5. We have found that both the paramagnetic–ferromagnetic austenitic transition (TC) and the ferromagnetic–antiferromagnetic martensitic transition (TM) are sensitively influenced by the boron addition: TC tends to increase, while TM decreases with increasing boron concentration. Temperature dependent X-ray diffraction in the range of 200–500 K clearly shows an evolution of the structural transformation from orthorhombic to cubic structure phase transition on heating for the x = 1 and 3 samples. Strikingly, the addition of boron atoms into the lattice favours the ferromagnetic ordering relatively to the antiferromagnetic arrangement below TM. This consequently affects on the magneto-structural transition as well as on the size of magnetocaloric effect.

A new metal oxyhydride; neodymium oxyhydride, NdHO, has been synthesized from a reactant mixture of metal hydride (CaH2 or NdH3) and neodymium oxide (Nd2O3). The unit cell dimensions decrease smoothly in the series from LaHO, CeHO, PrHO to NdHO, in line with the lanthanide contraction. The crystal structure of NdHO is described on the basis of Rietveld refinement on neutron powder diffraction data: Space group: P4/nmm (no. 129, D4h7). Axis lengths: a=7.8480(5) A, c=5.5601(8) A. Volume: V=342.46(6) A3. The tetragonal structure is derived from the fluorite structure, showing complete ordering of hydride and oxide ions over the anion sublatttice. The formation of NdHO was further substantiated by Raman spectroscopy.

The influences of the oxygen partial pressure and the LSM/YSZ ratio on the LSM–YSZ interface reactions at 1,000 °C were investigated. Both pellets and diffusion couples were employed in the study. The equilibrium thermodynamics of the LSM–YSZ reactions was clarified based on the pellet study–powder reaction. LSM reacts differently with YSZ in different atmospheres. In air, m-ZrO2 (monoclinic) is formed; while in N2, SrZrO3 and/or La2Zr2O7 are formed depending on the initial LSM/YSZ ratio. The reactions are reversible with varying P(O2) i.e. treating the sample in air after the heat treatment in N2 results in a decomposition of the formed La- and Sr-zirconates. The de-stabilisation of the LSM–YSZ interface under long-term annealing at 1,000 °C originates mainly from the inter-diffusion across the interface. Under reduced P(O2), the Mn diffusion from LSM into YSZ is enhanced. High P(O2) (≥0.21 atm) promotes the m-ZrO2 formation.

The changes in the cathode/electrolyte interface microstructure have been studied on anode-supported technological solid oxide fuel cells (SOFCs) that were subjected to long-term (1500 h) testing at 750 °C under high electrical loading (a current density of 0.75 A/cm 2 ). These cells exhibit different cathode degradation rates depending on, among others, the composition of the cathode gas, being significantly smaller in oxygen than in air. FE-SEM and high resolution analytical TEM were applied for characterization of the interface on a submicron- and nano-scale. The interface degradation has been identified as the loss of LSM coverage and the loss of three-phase-boundary (TPB) length. Firstly, the degradation is caused by the size reduction of the individual LSM/YSZ electrolyte contact points (areas) that are initially of 100–200 nm in diameter. Quantitative microstructure evaluation shows that in the cell tested in air this mechanism contributes to an estimated overall reduction in the LSM coverage and the TPB length by 50 and 30%, respectively. For the cell tested in oxygen the corresponding values are 10 and 4%. Secondly, in the cell tested in air the LSM coverage and the TPB length appear to decrease further due to the more pronounced formation of insulating zirconate phases that are present locally and preferably in LSM/YSZ electrolyte contact areas. The effects of the cathode gas on the interface degradation are discussed considering the change of oxygen activity at the interface, possible changes in the Mn diffusion pattern as well as the LSM/YSZ reactivity. Finally, based on thermodynamic calculations a T – p (O 2 ) diagram predicting the safe and risky operation conditions in terms of the zirconate formation is presented and compared with the experimental observations.

Electricity production from acetate, glucose and xylose with humic acid as mediator was investigated in two chambers microbial fuel cells (MFCs). Acetate produced the highest voltage (570 mV with 1000 Omega) and maximum power density (P(maxd)=123 mW/m(2)) due to a simpler metabolism than with glucose and xylose. Glucose and xylose resulted in P(maxd) of 28 mW/m(2) and 32 mW/m(2) at lower voltage of 380 mV and 414 mV, respectively. P(maxd) increased by 84% and 30%, for glucose and xylose respectively, when humic acid (2g/l) was present in the medium. No significant effect was found with acetate since the internal resistance possessed a limiting effect. The increase of P(maxd) due to humic acid presence was attributed to its ability to act as mediator. Even though pH decreased to 5 with glucose and xylose, due to production of acetate and propionate, the voltage remained on the same level of 250-350 mV.

Oxygen nonstoichiometry, structure and transport properties of the two compositions (La 0.6 Sr 0.4 ) 0.99 CoO 3− δ (LSC40) and La 0.85 Sr 0.15 CoO 3− δ (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, σ , of the materials is high ( σ > 500 S cm − 1 ) in the measured temperature range (650–1000 °C) and oxygen partial pressure range (0.209–10 − 4 atm). At 900 °C the electrical conductivity is 1365 and 1491 S cm − 1 in air for LSC40 and LSC15, respectively. A linear correlation between the electrical conductivity and the oxygen vacancy concentration was found for both samples. The mobility of the electron-holes was inversely proportional with the absolute temperature indicating a metallic type conductivity for LSC40. Using electrical conductivity relaxation the chemical diffusion coefficient of oxygen was determined. It was found that accurate values of the chemical diffusion coefficient could only be obtained using a sample with a porous surface coating. The porous surface coating increased the surface exchange reaction thereby unmasking the chemical diffusion coefficient. The ionic conductivity deduced from electrical conductivity relaxation was determined to be 0.45 S cm − 1 and 0.01 S cm − 1 at 1000 and 650 °C, respectively. The activation energy for the ionic conductivity at a constant vacancy concentration ( δ = 0.125) was found to be 0.90 eV.

Stack tests were run at 850 °C for periods from 80 hours to 1,150 hours to develop contacting procedures and at the same time evaluate the performance of a 5 μm electroplated nickel coating on a ferritic Fe22Cr interconnect. The metallic nickel coating reacted relatively quickly during the initial heating to 1,030 °C. During this time, 20–70 μm thick surface layers of austenitic steel were formed, which were covered by a 1–4 μm chromia layer on the anode side and by a layer of mixed Cr-Fe-Ni-spinels over a 1–4 μm chromia layer on the cathode side. The microstructure and composition of the protective scale on the cathode side was susceptible to pitting-type corrosion patterns, which may limit the life expectancy to less than 2,000 hours for the 200 μm thick interconnect tested. The initial area-specific resistances (ASR) at the interconnect/cathode current collector interface and the interconnect/anode current collector interface were very low (2 and 10 mΩ cm2, respectively). The cathode side interface resistance increased over the 1,150 hours by ∼7 mΩ cm2/103�h, but the anode side interface resistance decreased during the first 600 hours of the experiment before it started to show a slight increase

Sr0.7La0.3TiO3−α specimens were prepared in reducing atmosphere, and the structural and electrical properties were studied. The lattice parameter of Sr0.7La0.3TiO3−α at room temperature was larger than that expected from Vegard’s law between SrTiO3 and LaTiO3 due to the reductive expansion. The conductivity of this specimen was 100 S cm−1 at 1000°C, pO2 = 10−13 Pa. However, the conductivity was not preserved after an oxidation-reduction cycle. Over pO2 = 102 Pa, the conductivity drastically dropped with increasing pO2. The thermal expansion coefficient of Sr0.7La0.3TiO3−α was 11.8 × 10−6 K−1 in 9% H2/N2 (room temperature – 1000°C). In this Sr0.7La0.3TiO3−α, the chemical expansion on oxidation reached Δl/lo = 0.51%, when changing pO2 from 10−11 Pa to 2 × 104 Pa (air) at 1000°C.

In this study, La-doped SrTiO 3 specimens were prepared in air, and the structural and electrical properties were studied. The lattice parameter of the Sr 1– x La x TiO 3 , which was sintered at 1723–1923 K in air, increased proportionally with increasing x . This proportionality relation agreed with a Vegard's law between SrTiO 3 and LaTiO 3 . As a result of comparison with other literature data, it was proved that the lattice parameter in Sr 1– x La x TiO 3 is highly dependent on the condition of sample preparation. Sr 0.9 La 0.1 TiO 3 displayed a remarkable hysteresis in the temperature dependence of the conductivity under reducing atmospheres. On the other hand, Sr 0.7 La 0.3 TiO 3 showed very low dependence of the conductivity on temperature and P O 2 . It is considered that the presence of point defect clustering and/or Ruddlesden–Popper phase in highly La-doped SrTiO 3 specimens blocked the rapid diffusion of oxygen and electronic conduction between titanium ions.

Pr 0.7 Sr 0.3 Fe 1− x Ni x O 3− δ (PSFN; x =0.2–0.5) compounds were synthesized and characterized by powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) measurements, electrical conductivity and electrochemical impedance spectroscopy on cone-shaped electrodes on a Ce 0.9 Gd 0.1 O 1.95 (CGO10) electrolyte. The main phase of the powders belongs to the orthorhombic crystal system. The conductivities are fairly high, e.g., around 450 Scm −1 at 600 °C for the x =0.3 compound. The TEC of the compounds is close to the values of ceria-based electrolytes. PSFN showed hysteresis in the temperature dependence of the conductivity, TEC and area-specific polarization resistance R pol . It is considered that the hysteresis was caused by relatively slow adjustment of the oxygen stoichiometry. The electrochemical performance R pol −1 of the PSFN compounds is similar to that of La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3− δ .

Three high temperature structural phase transitions have been identified in the perovskite-structured phase SrSnO3 using differential scanning calorimetry and dilatometry, and have subsequently been structurally characterised using high-resolution neutron powder diffraction. Between 298 and 905 K, SrSnO3 is orthorhombic, space group Pmcn before undergoing a continuous phase transition to a second orthorhombic phase in space group Incn. At 1062 K there is a first order phase transition to a tetragonal phase in space group I4/mcm before finally transforming to the aristotype phase at 1295 K. Using the magnitude of the anti-phase tilt as a measure of the order parameter for the transition from I4/mcm to P m 3 ¯ m suggests this transition is tricritical in nature. Crystal structures are reported for the three hettotype phases.

Many metal oxides of fluorite and perovskite related structures are oxide ion conductors, which have practical applications in devices such as oxygen sensors, solid oxide fuel cells (SOFC) and electrolysers. Several structural and thermodynamic parameters such as (1) critical radius of the pathway for the oxide ion movement, (2) free lattice volume, and (3) average metal-oxide bond energy have been proposed as predictors of high oxide ion conductivity. We discuss how these parameters all depend on ionic radii, and therefore, some of these may be redundant. Furthermore, we explore the interrelations among such parameters for fluorite and perovskite oxides by considering their sensitivities to the individual ionic radii. Based on experimental data available in the literature, it is argued that lattice distortion (lattice stress and deviation from cubic symmetry) due to ion radii mismatch determines the ionic conductivity to a very large extent, and that lattice distortion is of much greater importance than many other proposed parameters. In case of the perovskites, the charge of the B-site ion is also of major importance.

The perovskites (La0.85Sr0.15)0.98CoO3 − δ and (La0.85Sr0.15)1.00CoO3 − δ have been investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical conductivity relaxation (ECR). This system was chosen in order to investigate the influence of cation vacancies on the transport properties in the materials. From ECR-measurements it is concluded that no difference in the chemical diffusion coefficient for oxide ions between the two samples can be found. The activation energy for the chemical diffusion coefficient has been found to be 107 ± 5 kJ mol− 1. However, the surface exchange coefficient differs between the two samples. The Co-rich sample has a significantly higher surface exchange coefficient than the A/B-stoichiometric sample. For both samples the surface exchange coefficient was almost independent of the temperature. At all temperatures the Co-rich sample had a significantly higher electrical conductivity. The difference in electrical conductivity between the two samples diminished when going to higher temperatures. Both materials can be assigned to a single phase hexagonal perovskite. An annealed sample of (La0.85Sr0.15)0.98CoO3 − δ did however contain an unidentified secondary phase on the surface.

Four types of cellulose, in particular carboxy methyl cellulose (CMC), are tested as potential binding materials in graphitic anodes for lithium ion batteries. It is shown that a minimum content of a cellulose which gives acceptable anode properties (reversible capacity>300 mA h g−1 during the first 10 cycles, irreversible loss

A short review of IR-spectroscopy on protons in perovskite structure oxides is given. The nature of possible proton sites, libration and combination tones and degree of hydrogen bonding is emphasised. Three new spectroscopic experiments and/or interpretations are presented. An IR-microscopy experiment was performed on the protonic conductor Ba3(Ca1+xNb2−x)O9−δ, x=0.18. The H/D concentration profile of a cross-section of the sample after partial isotopic exchange can be visualised; proton containing La0.9Ca0.1ErO3 was studied up to 200 °C by Raman spectroscopy. At 200 °C, the OH-stretch cannot be observed due to thermal broadening, but the peak reappears upon cooling; the OH and OD absorption bands in BaCe1−xNdxO3 are very broad and, in addition, an electronic transition of Nd+3 is observed at 1900–1930 cm−1; finally, IR reflectance spectroscopy on BaZr0.9Y0.1O3, La0.8Sr0.2ScO3, La0.9Sr0.1Sc0.9Mg0.1O3 and SrCe0.95Y0.05O3 shows at least three types of proton positions.

The chemical and physical nature of the hydride ion is briefly treated. Several reactions of the hydride ion in oxides or oxygen atmosphere are given. A number of perovskites and inverse perovskites are listed, which contain the H − ion on the oxygen or B-anion sites in the archetype ABO 3 system. H − is stable with respect to oxide and halide anions but, among cations only with respect to oxides and halides of strongly electropositive metals such as alkaline, alkaline-earth and main group III metals. H − is only stable in combination with transition metal ions of certain elements in their lowest positive oxidation state. Mixed oxide/hydride containing perovskites may thus exist. Steinsvik et al. have recently suggested a defect model for a perovskite including substitutional hydride ions on the oxygen site, H O ⋅ , and protons associated with a lattice oxygen, OH O ⋅ . The defect equations for this acceptor doped A(II)B(IV)O 3 model compound are solved without using the conventional Brouwer approximations. One case is presented where hydride formation is suppressed, and another case where it is promoted. Plots of concentration versus water and oxygen partial pressures show new interesting features; these are discussed.

Pyrochlore oxides of the composition Y2Ti2−yZryO7, with y= 0, 0.3, 0.6, and 0.9, were studied using Raman spectroscopy. Doping with Zr+4, a homovalent ion, gradually induces the material to undergo a structural change from the perfect pyrochlore structure to a defect pyrochlore structure and ends at an oxygen deficient fluorite structure with the formula (Y, Ti, Zr)1O1.75. Invoking the bigger Zr+4 ion on the Ti+4 site causes this structural transformation. We have also investigated highly Ti-doped YSZ ceramic samples, which all have an oxygen deficient cubic fluorite structure. These samples have formula units between (Y, Ti, Zr)1O1.675 and (Y, Ti, Zr)1O1.90. It is argued that a band observed at 750 cm−1 in both the Ti-doped pyrochlore samples and in the Ti, Y, Zr fluorite samples is due to oxygen in seven fold coordination around Ti. Local structures are accordingly observed by Raman in these samples. We finally report a Raman spectrum of orthorhombic Y2TiO5. A defect chemistry model has been formulated, which qualitatively describes the observed pyrochlore–fluorite structural transition.

The densification, microstructure and phase evolution of Sr4Fe6−xCoxO13 (0≤x≤4) materials have been investigated by powder X-ray diffraction, electron microscopy and thermal analysis. Powders were prepared by the solid state reaction method or by the EDTA precursor method. Pure Sr4Fe6O13 is stable above 775±25°C in air until it melts peritectically at 1220±5°C. Below 775°C, Sr4Fe6O13 is unstable with respect to the formation of Sr1−xFeO3−δ and SrFe12O19. Co substituted Sr4Fe6O13 is only stable in a narrow temperature region near 900°C. At higher or lower temperature, the Co-content is reduced due to formation of the perovskite SrFe1−zCozO3−δ and the solid solutions Co3−yFeyO4 (below 900°C) or Co1−yFeyO (above 900°C). A plate-like morphology of Sr4Fe6−xCoxO13 grains was observed both in calcined powders and in sintered ceramics. Ball milling of the calcined powders was necessary prior to the sintering in order to achieve dense materials in the temperature region 1120–1170°C. Only pure Sr4Fe6O13 appeared as a single-phase material after sintering. Increasing amounts of the phases SrFe1−zCozO3−δ and Co1−yFeyO were observed with increasing sintering temperature and increasing Co-content due to the limited solubility of Co in Sr4Fe6−xCoxO13. The thermal expansion coefficient of the materials deviates from linear behavior due to the decreasing oxidation state of iron with increasing temperature. The present investigation demonstrates that Sr4Fe4Co2O13 materials with high oxygen permeability are not single-phase materials when sintered at high temperature.

Pyrochlores with praseodymium as the A-site cation and zirconium, tin, cerium and manganese cations on the B-site were prepared in air and their electrical conductivities were investigated as a function of oxygen partial pressure and temperature. Pure Pr2Zr2O7±δ as well as samples modified on the B-site with 5% Mn or 20% Ce show conductivities, which are lower than 2×10−3 S/cm at 1000°C in H2/H2O atmospheres. Electronic p-type conductivity was indicated for these materials in oxygen/nitrogen mixtures. The electrically conducting pyrochlore solid solutions Gd2TiMoO7±δ and Gd2Ti0.6Mo1.4O7±δ were synthesised and investigated in 1% H2/3% H2O/96% N2. No formation of a new phase by reaction with YSZ was indicated after exposure to this atmosphere at 1000°C for 1000 h. Pr2Sn2O7±δ modified with 5% indium on the B-site exhibited a conductivity in air of 6.5×10−3 S/cm at 1000°C. The pure material was found to decompose in mixtures of 9% H2/3% H2O/88% N2.

Two precise algorithms are devised for the calculation of defect concentrations in A-site acceptor doped ABO 3 perovskites. The two models contain nine species including cation vacancies on the A- and B-site. The small polaron model is based on three redox levels of the B-ion. A large polaron model, based on delocalised electrons, electron holes and all B-ions being trivalent is given in Appendix A . The sequential mathematical method allows us to calculate the high temperature oxygen partial pressure dependent properties of (La 1− x Sr x ) y MnO 3± δ in a unified manner irrespective of the type of defect regime. Simulations are shown for a pO 2 span from 10 −30 to 10 5 atm. The three required equilibrium constants for (La 1− x Sr x ) y MnO 3± δ had to be changed significantly from values given in literature in order to match the observed stoichiometry span. The main results shown are calculated by the small polaron model containing only ionic species – the B-ion may be Mn B ′ (Mn 2+ ), Mn B x (Mn 3+ ), and Mn B ⋅ (Mn 4+ ). The A/B-ratio= y greatly influences the oxygen stoichiometry, oxygen ion vacancy- and cation vacancy concentrations and the total conductivity. Calculations are given for the range 0.87≤ y ≤1.13 for a Sr doping of 10% at 1000°C. The defect model can simultaneously describe the observed stoichiometry and conductivity dependence on pO 2 , if the electronic mobility is decreased by up to 50% at pO 2 −10 and pO 2 >10 −2 atm.

The conductivity of the materials LaAlO3, LaGaO3, LaScO3 and LaInO3 all doped with 10% strontium on the A-site and 10% magnesium at the B-site has been measured at different temperatures and oxygen partial pressures. The doped LaGaO3 is found to be an almost pure ionic conductor with a conductivity of 95 mS/cm at 800°C. The conductivity of doped LaGaO3 decreases with time due to precipitation of a secondary phase. The doped LaAlO3 and LaScO3 are mixed conductors in oxidising atmosphere. Their ionic conductivities at 800°C are 1.3 and 0.5 mS/cm, respectively. The conductivities given are total conductivities. The large difference in the conductivities of the investigated materials seems to be caused partly by grain boundary resistance.

The prospects of using mixed ionic/electronic conducting ceramics for syngas production in a catalytic membrane reactor are analysed. Problems relating to limited thermodynamic stability and poor dimensional stability of candidate materials are addressed. The consequences for these problems, of flux improving measures like minimization of membrane thickness and minimization of the losses due to oxygen exchange over the membrane surfaces, are discussed. The analysis is conducted on two candidate materials: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- δ and SrFeCo 0.5 O x . Finally, experimental investigations of the dimensional stability of the latter material under reducing conditions are reported.

The acceptor-doped perovskite proton conductor SrCe 1− x Y x O ξ ( x =0.025 to 0.20, ξ =3− x /2) has been prepared and characterised using X-ray diffraction and AC impedance spectroscopy, and the effect of the yttrium dopant concentration on structure and electrical properties has been investigated. X-ray diffraction studies show a decrease in lattice volume with increasing yttrium content. Electrical conductivity studies have been made as a function of oxygen partial pressure, and at a partial pressure of water vapour of 0.007 atm. The total conductivity has been separated into different components by fitting procedures and regions of ionic and p-type conduction have been identified. At 800°C and at the water vapour partial pressure of 0.007 atm, the ionic conductivity showed a maximum at a doping level of x =0.10, reaching a value of 5 mS/cm. The conductivity component appearing at low oxygen partial pressure, which according to recent studies may be regarded as protonic rather than n-type, decreased with doping, while the p-type component at high oxygen partial pressure increased. The relationship between the effect of doping on the conductivity and unit cell volume is discussed.

2MgO–Al2O3–3.3P2O5 glasses with increasing amounts of SiO2 are considered for sealing applications in solid oxide fuel cells (SOFC). The change in chemical durability under SOFC anode conditions and the linear thermal expansion are measured as functions of the SiO2 concentration. Raman spectroscopy analysis of the glasses reveals no sign of important changes in the glass structure upon SiO2 addition. Some increase in glass durability with SiO2 concentration is reported and its cause discussed.

A general numerical method for calculation of concentrations of vacancies and ionic and electronic defects in solids in equilibrium with two gas pressures is presented. The method is applied to 5 at% B-site doped SrCeO3in equilibrium with oxygen and water vapor. The model includes protons and electronic defects, as well as cation vacancies on theAandBsites. The 10 concentrations in the model are determined uniquely by solving the linear and mass action law type equations in a rational sequence. No approximations or truncations of the equations are necessary. No information on the magnitude of the Schottky-equilibrium constant,Ks, controlling the population of cation vacancies is available. Limiting values ofKswere tested to illustrate suppression and enhancement of cation vacancy formation in perovskites. Deviations from Sieverts law are demonstrated. Deviation of theA/Bratio from unity has the same effect on the proton content as an increase of the dopant level.

Acceptor doped perovskites such as strontium cerate form a variety of point defects through reaction with surrounding gases at high temperature, namely protons by dissolution of water vapour, electron holes by dissolution of oxygen and electrons by loss of oxygen. The defect equilibria can be described by three equilibrium constants coupled with electroneutrality and site conservation constraints. This work describes a numerical solution of these equations for arbitrary oxygen and water vapour partial pressures, without the need to neglect minority defects. It further examines the charge compensation mechanisms that dominate under the different regimes and their implications for transport properties.

Thermoelectric power and electrical conductivity of pure and 5, 10 and 20% strontium-doped lanthanum manganite are determined as function of temperature in air and of P o 2 at 1000 °C. At high temperatures the thermoelectric power is negative. Both thermoelectric power and conductivity are found to be nearly independent of doping at high temperatures, but not at low. This can be explained if it is assumed that Mn 3+ disproportionates into Mn 2+ and Mn 4+ . In reducing atmospheres the thermoelectric power is found to be only slightly dependent on P o 2 , which also might be explained by the disproportionation reaction.

Thermoelectric power and electrical conductivity of CeO 2 doped with 2.5, 5 and 20 mole % CaO and 10 mole% Gd 2 O 3 were determined as function of oxygen partial pressure (Po 2 ) at 1000 °C and as function of temperature at three different Po 2 s. The conductivity measurements show ionic conduction at high Po 2 2 and n -type conduction in reducing atmospheres. The thermoelectric power is positive in the ionic conducting regime and negative for the n -type conduction. The thermoelectric power depends on temperature, except for very low Po 2 , and shows a contribution from electronic conduction already at very small electronic transference numbers.

It is shown how the thermoelectric power of an oxide with pure oxide ion vacancy conduction can be derived. The result differs somewhat from earlier works on the same subject. Measurements of the thermoelectric power of yttria-stabilized zirconia at 1000 °C were performed as a function of dopant concentration. The results of the measurement are presented together with literature data. They are found to be in acceptable agreement with the presented theory.

Thermoelectric power and electrical conductivity of LaAl 0.95 Mg 0.05 O 3-8 and ErAl 0.95 Mg 0.05 O 3-δ have been determined as a function of oxygen partial pressure between 1 and 10 -15 atm at 1000°C and as a function of temperature in air and in a hydrogen-water buffer. In oxidizing atmospheres these compounds are found to be p-type conductors and in reducing atmospheres ionic conductors. The thermoelectric power at 1000°C depends strongly on oxygen partial pressure. In both reducing and oxidizing atmospheres the thermoelectric power depends on temperature. In this work a new method for calculating ionic transference numbers directly from measurements of the thermoelectric power is discussed.

Rb2SeO4 is synthesized by slow evaporation of aqueous solutions of Rb2CO3 and H2SeO4 (50 °C, 2 d) and characterized by calorimetry, impedance spectroscopy, and powder XRD.

Membrane electrode assemblies (MEAs) were incorporated into the cathode chamber of a submersible microbial fuel cell (SMFC). A close contact of the electrodes could produce high power output from SMFC in which anode and cathode electrodes were connected in parallel. In polarization test, the maximum power density was 631 mW/m 2 at current density of 1772 mA/m 2 at 82 Ω. With 180-Ω external resistance, one set of the electrodes on the same side could generate more power density of 832 ± 4 mW/m 2 with current generation of 1923 ± 4 mA/m 2 . The anode, inclusive a biofilm behaved ohmic, whereas a Tafel type behavior was observed for the oxygen reduction. The various impedance contributions from electrodes, electrolyte and membrane were analyzed and identified by electrochemical impedance spectroscopy. Air flow rate to the cathode chamber affected microbial voltage generation, and higher power generation was obtained at relatively low air flow less than 2 mL/min.

The Seebeck coefficient of nine strontium ferrate ceramics with the nominal compositions: SrFeyO3−x (where y=0 .909, 0.952, 1, 1.05, 1.10), and NazSr1−zFeO3−x and LazSr1−zFeO3−x (where z=0.05, 0.1) were measured in air from 300–1000°C. The deficiency in oxygen stoichiometry, x, adjusts itself in air from approximately 0.15 to 0.35 in this temperature range. Most of the materials have reasonably high electronic conductivities, and some samples of lanthanum-doped ferrate reached conductivities of 50–90 S/cm at 25°C. The total spread in conductivity between the 9 samples was 4 decades at 25°C. Negative temperature coefficients for the total conductivity were observed above 5–600°C. The thermopowers (−5 to +120 μV/K) show similar (strong) temperature dependencies for all materials and increase with increasing temperature. The temperature dependency of conductivity and thermopower can be explained by the strong variation of oxygen content (hole concentration decreases with increasing temperature). A simple defect model for SrFeO3−x at high PO2 was consistent with the observed oxygen partial pressure dependence of the conductivity at 800°C.

Thermoelectric power of an yttria stabilized zirconia (YSZ) thermocell, Pt|YSZ|Ptm has been determined at 1273 K in different atmospheres. The atmospheres used have been mixtures of O2-inert gases, CO-CO2 and H2-H2O. Oxygen partial pressures ranged between 1 and 10-21 atm. The yttria content in the YSZ was 8 mol%. The dependence on temperature of the thermoelectric power of YSZ in air has also been measured between 600 and 1100°C. The thermoelectric power was determined to be 0.486 mV/K in air at 1 atm, the colder end was positive relative to the hotter end. The transported entropy of O2- in yttria-stabilized zirconia is calculated from a combination of thermodynamic and measurement data and is found to be 33 JK-1 mol-1, independent of oxygen partial pressure and temperature. It is shown that the major contribution to the measured thermoelectric power comes from the entropy change of the electrode reactions. It is possible, from the thermoelectric power of a YSZ thermocell, experimentally to determine approximative values of the single electrode reversible heat evolution in an SOFC. These calculations give that 60 kJ/mol e- will be evolved at the cathode when air is the cathode gas and 41 kJ/mol e- will be consumed at the anode in a mixture of 98% H2 and 2% H2O, at 1273 K when the total gas pressure at both cathode and anode is 1 atm.

NdHO is synthesized by solid state reaction of CaH2 or NdH3 and Nd2O3 (Ar/7% H2, 650 °C, 20 h) and characterized by neutron powder diffraction and Raman spectroscopy.

Vanadium oxide films have been prepared by RF-sputtering using an oxygen containing sputter gas and a V2O5 target. The main component of these films is orthorhombic V2O5 with poor crystallinity and a tendency for ordering of the crystallites with the c-direction parallel to the substrate. All films were oxygen deficient compared to V2O5. Films prepared in pure argon were reduced to V(4) or lower. The vanadium oxide films were tested in solid-state lithium cells. Films sputtered in oxygen showed electrochemical properties similar to crystalline V2O5. The main differences are a decreased capacity above 3.0 V, showing that V is partially reduced, and a broadening of the capacity peaks, showing that the crystallinity of these films is rather low. The film sputtered in argon behaved differently, discharging at a very low potential, 1.9 V versus Li, in the first cycle. In subsequent cycles the average insertion potential was increased due to a structural distortion of the host.

The formation of the strontium zirconates SrZrO 3 , Sr 4 Zr 3 O 10 , Sr 3 Zr 2 O 7 and Sr 2 ZrO 4 , and of the lanthanum zirconates La 2 Zr 2 O 7 and La 2− x Y x Zr 2 O 7 at 1450°C was investigated by x -ray powder diffraction and DTA. Three different routes of synthesis were tested. In the Sr-zirconate system, single phase orthorhombic SrZrO 3 and somewhat impure, tetragonal Sr 2 ZrO 4 were observed, whereas the formation of ordered Ruddlesden-Popper phases, Sr n Zr n −1 O 3n−2 , where n=4 and 3, could not be verifi ed. The conductivity of La 2 Zr 2 O 7 was 3.7×10 −6 S/cm at 750°C and 3.8×10 −5 S/cm at 1000°C. The conductivity of the Sr-zircon ates increases with increasing Sr/Zr ratio. Samples with a nominal composition corresponding to Sr 2 ZrO 4 have a conductivity of 7.5×10 −5 and 5.9×10 −4 S/cm at 750 and 1000°C, respectively. For all samples one observes low activation energies for ionic conduction (0.5–0.65 eV). Formation of pyrochlore structure La 2− x Y x Zr 2 O 7 from YSZ and La 2 O 3 at 1450 °C was demonstrated.

PrFe 1− x Ni x O 3− δ ( x = 0.4–0.6) compounds were synthesized and characterized by powder XRD, electrical conductivity and electrochemical impedance spectroscopy on point electrodes on a Ce 0.9 Gd 0.1 O 2− δ (CGO10) electrolyte. As a reference, the electrochemical performance of LaFe 0.4 Ni 0.6 O 3− δ was also measured. The main phase in the PrFe 1− x Ni x O 3− δ series was perovskite-type structure and belonged to the orthorhombic crystal system. The conductivities are fairly high, e.g. around 220 S cm −1 at 873 K for the x = 0.4 compound. The electrochemical performance of the PrFe 1− x Ni x O 3− δ series is similar to that of La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3− δ , which is a good candidate as a cathode material for SOFCs operating at intermediate temperature. The electrochemical performance of LaFe 0.4 Ni 0.6 O 3− δ was even higher than that of the PrFe 1− x Ni x O 3− δ series and the polarization resistance was 0.14 Ω cm 2 at 1073 K measured on a point electrode.

Electrode tests and ac impedance measurements presented by Pound on Ni, Co and Mn doped CeO2 are reviewed. We find that the stability of solid solutions in the systems of NiO-CeO2 and CoO-CeO2 are improbable and that therefore the interpretation of ac impedance data and electrode tests should be in terms of two-phase systems.

The formalism developed here furnishes means by which ionic configurations, solid solution limits, and conductivity mechanisms in doped fluorite structures can be described. The present model differs markedly from previous models but reproduces qualitatively reality. The analysis reported is for the case of a MO 2 oxide doped with a divalent oxide MeO.