Published references
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ID=589| Authors |
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Electrochimica Acta
Volume: 361,
Pages: 137019 Time of Publication: 2020 |
| Abstract | The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in LixTaOy thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 °C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt)5), lithium tert-butoxide (LiOtBu) and water as reactants. The film composition was determined by time-of-flight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity σRT of ~10−8 S cm−1 is obtained for a 169 nm thick Li0.98TaOy film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed. |
| Keywords | Atomic layer deposition; LixTaOy thin films; Solid-state electrolytes; TOF-ERDA; Ionic conductivity |
| Remark | Link |
Examination of Dielectric Properties of BaTiO3-SrTiO3 Based Systems
ID=588| Author |
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Time of Publication: 2020
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| Abstract | This thesis examines the dielectric properties of two systems based on the perovskite materials barium titanate and strontium titanate. A solid solution was created starting with these base materials and then adding varying amounts of bismuth-zinc titanateand sodium niobate. These compositions were calcined and sintered at temperatures determined to be the most phase-pure by x-ray diffraction. Sintered pellets were then tested using equipment to measure their capacitance as a function of temperature and their strain as a function of applied electric field. From these results and the x-ray diffraction data the lattice parameter and dielectric constant was calculated. The system with sodium niobate had the highest capacitance and dielectric constant overall. The composition with the highest capacitance, greater than 4nf at room temperature at all tested frequencies, and dielectric constant, greater than 4000 at all tested frequencies, was 68.6 mol% barium titanate, 29.4 mol% strontium titanate, and 2 mol% sodium niobate. |
| Remark |
A THESIS, Baccalaureate of Science in Electrical and Computer Engineering Link |
Structural and Electrochemical Properties of Tysonite Ce0.95A0.05F2.95 (A = Mg, Ca, Sr, and Ba): Fast-Fluoride-Ion-Conducting Solid Electrolytes
ID=587| Authors |
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J. Phys. Chem. C
Volume: 124,
Issue: 34,
Pages: 18452–18461 Time of Publication: 2020 |
| Abstract | All-solid-state fluoride shuttle batteries (FSBs) present endless possibilities for next-generation rechargeable batteries. However, no standard choice for solid electrolytes and electrodes in FSBs has been established to date. Additionally, details of how F ions travel through the working device are yet to be fully understood. Here, we studied the electrochemical properties of tysonite Ce0.95A0.05F2.95 (A = Ca, Sr, and Ba) and Ce0.95Mg0.05F2.95 (actually, a composite of CeF3 and MgF2) solid electrolytes, and their crystal structures using neutron diffraction data. In particular, Ce0.95Ca0.05F2.95 exhibited the highest electrical conductivity and the shortest bond between F ions. Furthermore, F-vacancies introduced by the substitution of Ca2+ for Ce3+ were accommodated only at the F1 site. The bond valence sum (BVS) analysis results indicated that there was a significant difference in the BVS values of F ions: BVS(F1) = −0.92 on [F1] layers, and BVS(F2) = −1.13 and BVS(F3) = −1.07 on [M (=Ce0.95Ca0.05), F2, F3] layers, which were stacked alternately along the c-axis of the trigonal cell. The BVS(F2) value was relatively lower than the BVS(F1) and BVS(F3) ones, indicating that F2 is tightly bonded to M compared to that of F1 or F3. The findings suggested that F1–F1 and F1–F3 sublattices play a key role in the high mobility of the conducting F ions. |
| Remark | Link |
Synthesis, structure, magnetic behavior and dielectric relaxation of the LaxSr2-xFeхTi1-хO4 (х = 0.5, 0.7) oxide ceramic
ID=586| Authors |
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Journal of Solid State Chemistry
Volume: 292,
Pages: 121687 Time of Publication: 2020 |
| Abstract | This study is devoted to the investigation of the high dielectric constant causes in complex oxides with a structure of the K2NiF4 type. А new thermobaric treated ceramics on the basis conjugate LaxSr2-xFeхTi1-хO4 (х = 0.5, 0.7) solid solutions was synthesized and the study their structure, microstructure, magnetic and dielectric properties was performed. It is shown that antiferromagnetic interactions coexist with ferromagnetic, which become dominant towards to low temperatures; the appearance of two types of magnetic interactions may be related to the presence of magnetic ions of different valences. Different values of the dielectric constants ε are observed in wide region of frequencies 10–107 Hz. In obtained at ambient pressure LaxSr2-xFeхTi1-хO4 (х = 0.5, 0.7) ceramics the highest permittivity ε value is only 30–50 in the frequency range from 1 kHz to 1 MHz. After the samples treatment at 1273 K and P = 4 GPa during 5 min ε increases to 5–102–103 at 293 š and independent of frequency in the range (102–106) Hz. At the temperature increase the permittivity as well increases and the ε value becomes ~106 at, approximately, f = 100 Hz and T = 750 K. An obvious change of samples microstructure and polyhedra structure anisotropy in LaxSr2-xFeхTi1-хO4 (х = 0.5, 0.7) was observed after the thermobaric treatment. Described in this article performed dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure, microstructure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and small polaron hopping conduction mechanism. |
| Keywords | Complex oxides; Synthesis; Ceramics; High pressure; Magnetization; Dielectric properties |
| Remark |
https://doi.org/10.1016/j.jssc.2020.121687 Link |
Structural and Electrochemical Properties of Tysonite Ce0.95A0.05F2.95 (A = Mg, Ca, Sr, and Ba): Fast-Fluoride-Ion-Conducting Solid Electrolytes
ID=585| Authors |
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| Source |
J. Phys. Chem. C
Volume: 124,
Issue: 34,
Pages: 18452–18461 Time of Publication: 2020 |
| Abstract | All-solid-state fluoride shuttle batteries (FSBs) present endless possibilities for next-generation rechargeable batteries. However, no standard choice for solid electrolytes and electrodes in FSBs has been established to date. Additionally, details of how F ions travel through the working device are yet to be fully understood. Here, we studied the electrochemical properties of tysonite Ce0.95A0.05F2.95 (A = Ca, Sr, and Ba) and Ce0.95Mg0.05F2.95 (actually, a composite of CeF3 and MgF2) solid electrolytes, and their crystal structures using neutron diffraction data. In particular, Ce0.95Ca0.05F2.95 exhibited the highest electrical conductivity and the shortest bond between F ions. Furthermore, F-vacancies introduced by the substitution of Ca2+ for Ce3+ were accommodated only at the F1 site. The bond valence sum (BVS) analysis results indicated that there was a significant difference in the BVS values of F ions: BVS(F1) = −0.92 on [F1] layers, and BVS(F2) = −1.13 and BVS(F3) = −1.07 on [M (=Ce0.95Ca0.05), F2, F3] layers, which were stacked alternately along the c-axis of the trigonal cell. The BVS(F2) value was relatively lower than the BVS(F1) and BVS(F3) ones, indicating that F2 is tightly bonded to M compared to that of F1 or F3. The findings suggested that F1–F1 and F1–F3 sublattices play a key role in the high mobility of the conducting F ions. |
| Remark | Link |
Structural characterization and electrical/electrochemical studies of Nd1-xBaxCo1-y(Fe, Ti)y O3-δ (0 ≤ x ≤ 0.3, y = 0, 0.2) materials as cathode for SOFCs application
ID=584| Authors |
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Journal of Solid State Chemistry
Volume: 292,
Pages: 121682 Time of Publication: 2020 |
| Abstract | Perovskite oxide powders of Nd1-xBaxCo1-y (Fe, Ti)y O3-δ (0 ≤ x ≤ 0.3, y = 0, 0.2) were synthesized by combustion technique and investigated as cathode materials for SOFCs application. The Rietveld refinement of the XRD data confirms the formation of single phase orthorhombic perovskite structure of Pbnm space group within the compositions (0 ≤ x ≤ 0.1, y = 0, 0.2). The microstructural studies revealed the grains generated are irregular in shape and non uniform in size in the micrometer range. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Co3+/Co4+, Fe3+/Fe4+, Ti4+/Ti3+ and O-Lattice/O-Chemisorbed/O-physisorbed species. The measured average CTE values are varies from 18–25 × 10−6 K−1 in the temperature range 200–900 °C for all the synthesized samples. The electrical conductivity values are found to be 252 Scm−1, 308 Scm−1, 157 Scm−1 at 700 °C for the compositions Nd0.9Ba0·1CoO3-δ (NBC 0.1), Nd0.9Ba0·1Co0·8Fe0·2O3-δ (NBCFO), Nd0.9Ba0·1Co0·8Ti0·2O3-δ (NBCTO), respectively. XRD analysis reveals no chemical reactivity for the compositions NBCFO, NBCTO with 20 mol% gadolinium doped ceria oxide (Ce0.8Gd0.2O2−δ) electrolyte material after firing at 1200 °C for 8 h. The area specific resistances (ASR) were calculated for the symmetrical cells and are found to be 0.67 Ω cm2, 1.07 Ω cm2 at 850 °C for the NBCFO, NBCTO compositions, respectively. Among the compositions evaluated Nd0.9Ba0·1Co0·8Fe0·2O3-δ showed highest total electrical conductivity ~308 Scm−1 and lowest ASR value ~0.67 Ωcm2 compared to all other compositions. Hence the result suggests the synthesized Nd0.9Ba0·1Co0·8Fe0·2O3-δ composition could be a promising cathode material for SOFCs application. |
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Effect of the Complexing Agent in the Pechini Method on the Structural and Electrical Properties of an Ionic Conductor of Formula La1−xSrxAlO3−δ (x = 0, 0.05, 0.1, 0.15)
ID=583| Authors |
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Advances in Renewable Hydrogen and Other Sustainable Energy Carriers
Pages: 387-393 Time of Publication: 2020 |
| Abstract | The Ion conductors are used as electrolytes in high temperature Solid Oxide Fuel Cells SOFCs. The preparation route has an important role on their structural and electrical properties. In this study, we used a modified Pechini method to prepare an ionic conductor based on lanthanum aluminate doped with strontium La1−xSrxAlO3−δ (x = 0.0.05, 0.1, 0.15). The effect of two complexing agents on structural and electrical properties was studied, we used Ethylene Diamine Tetra Acetic EDTA, and tartaric acid TA as complexing agents. The perovskite phases were obtained at 900 °C and characterized by different techniques; SEM images show that grain size is in the nanometer range, XRD analysis shows that the compounds prepared by use of the two complexing agents crystallize in a perovskite structure with an orthorhombic system and an R3m space group, the doped phases prepared by EDTA have a secondary phase LaSrAl3O7 which is absent in the compounds prepared by tartaric acid. The determination of the ionic conductivity by electrochemical impedance spectroscopy shows clearly the effect of the complexing agent. Indeed we have found that the value of the ionic conductivity is higher for the phases produced by the Pichini method in the presence of tartaric acid as complexing agent. |
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High Cu content LaNi1-xCuxO3-δ perovskites as candidate air electrode materials for Reversible Solid Oxide Cells
ID=582| Authors |
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International Journal of Hydrogen Energy
Volume: 45,
Issue: 53,
Pages: 29449-29464 Time of Publication: 2020 |
| Abstract | High Cu content perovskite-type LaNi1-xCuxO3-δ oxides are evaluated as alternative air electrode materials for Solid Oxide Cells. Auto-combustion synthesis allowed to obtain fine oxide powders up to a Cu content of x = 0.75 under ambient pressure. Investigations of the crystal structure, oxygen deficiency, chemical and thermal stability, as well as transport properties reveal satisfactory characteristics, with high total electrical conductivity and high concentration of oxygen vacancies at elevated temperatures. LaNi1-xCuxO3-δ-based electrode layers show low polarization resistance values in La0.8Sr0.2Ga0.8Mg0.2O3-δ-based symmetrical cells. The lowest values for Cu-rich compositions at 800 °C are 0.056 Ω cm−2 for LaNi 0.5Cu0.5O3-δ and 0.054 Ω cm−2 for LaNi0.25Cu0.75O3-δ with La0.2Ce0.8O3-δ buffer layer. For the reversible cell with LaNi0.5Cu0.5O3-δ air electrode, approx. 870 mW cm−2 power density output at 900 °C is obtained when fueled with wet H2, as well as over 3 A cm−2 current density at 2 V in the electrolysis mode. |
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Electrical properties of gadolinia-doped ceria for electrodes for magnetohydrodynamic energy systems
ID=581| Authors |
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SN Applied Sciences
Volume: 2
Time of Publication: 2020
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| Abstract | High temperature conducting ceramics are of current interest for use as electrode materials for magnetohydrodynamic (MHD) power generation systems for their high conductivity values and their excellent stability under extreme conditions including operating temperatures above 2000 °C. Ceria doped with Gd (GDC) has been extensively studied for intermediate temperature applications and shows promise as an efficient electrode material. A summary of the current understanding of the electrical properties of GDC is provided with an emphasis on the higher temperature limits. Experiments to further validate the conclusions drawn in the literature review confirm that with electrical conductivities near 10 S/m at 1100 °C make GDC a good candidate electrode material for an MHD power generator. |
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Domain wall conductivity as the origin of enhanced domain wall dynamics in polycrystalline BiFeO3
ID=580| Authors |
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Journal of Applied Physics
Volume: 128,
Pages: 064104 Time of Publication: 2020 |
| Abstract | Despite their primary importance in modern nanoelectronics, conductive domain walls (DWs) can also have a marking effect on the macroscopic response of polycrystalline ferroelectrics. In particular, a large nonlinear piezoelectric response at sub-Hz driving-field frequencies has been previously observed in BiFeO3, which was linked to the conductive nature of the DWs but whose exact origin has never been explained. In this study, by carefully designing the local conductivity in BiFeO3 using chemical doping, we found that the low-frequency piezoelectric nonlinearity is only observed in the sample with a large fraction of conductive DWs. Supported by nonlinear Maxwell–Wagner modeling, we propose that this large response originates from DW displacements inside a specific set of grains or grain clusters in which the internal electric fields are enhanced due to M-W effects. We thus show that these effects likely arise due to the pronounced local anisotropy in the electrical conductivity, varying from grain to grain, whose origin lies in the conductive DWs themselves. The results demonstrate the possibility of controlling the global nonlinear properties of polycrystalline ferroelectrics by engineering local properties. |
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Thermal, optical and electrical properties of MnO2-doped mixed sodium potassium phosphate glasses
ID=579| Authors |
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Journal of Thermal Analysis and Calorimetry
Time of Publication: 2020
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| Abstract | Glasses in the system (1 − x)(0.5NaPO3–0.5KPO3)–xMnO2, with 0 ≤ x ≤ 50 mol%, have been prepared using a melt-quench route. The glasses exhibit a yellow to dark color with the increase in manganese content owing to the presence of Mn2+ and Mn3+ ions in the network. The amorphous state of the glasses is evidenced by the X-ray diffraction. In order to get an insight into the physical and structural aspects of these vitreous materials, we have determined some of their parameters such as density, molar volume and glass transition temperature. From differential thermal analysis scan on heating, we evaluated the glass transition temperature (Tg) of each glass, which corresponds to the phase transition temperature from solid to viscous liquid. The density (ρ) as a structural index is found to increase while the corresponding molar volume decreases with MnO2 content. The structural approach of the studied glasses is evaluated by infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies. IR technique allowed us to identify the coexisting bond vibration modes in the glass network, and it has shown that many structural phosphates units coexist, mainly pyrophosphate and metaphosphate structural groups. EPR experiments have shown the presence of Mn2+ centers in the glasses. The UV–Visible absorption is utilized to estimate the values of the optical band gap (Eg) and Urbach energy (ΔE). The optical band gap energy is determined from both the absorption spectrum fitting (ASF) and Tauc’s methods. These optical parameters are composition dependence. The dc conductivity of the glasses is determined in the temperature range from 303 to 473 K. It decreases with increasing manganese content. It is thermally activated and followed an Arrhenius behavior. The crystallization of glasses is realized by submitting them to heat treatments, and the crystallized phases are identified by XRD analysis. The crystallization kinetic was studied under non-isothermal conditions. The activation energy (Ec) and the Avrami parameter (n) were determined. |
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In-situ Ni exsolution from NiTiO3 as potential anode for solid oxide fuel cells
ID=578| Authors |
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International Journal of Hydrogen Energy Volume: 45, Issue: 43 Time of Publication: 2020 |
| Abstract | Sample NiTiO3 (NTO) is prepared by the molten salts synthesis route as a potential anode material for solid oxide fuel cell (SOFC) applications. An additional sample impregnated with 5 mol%Ni (N-NTO) is also presented. Structural characterization reveal a pure NiTiO3 phase upon calcination at 850 °C and 1000 °C. Redox characterization by temperature programmed reduction tests indicate the transition from NiTiO3 to Ni/TiO2 at ca. 700 °C. Ni nanoparticles (ca. 26 nm) are exsolved in-situ from the structure after a reducing treatment at 850 °C. Catalytic activity tests for partial oxidation of methane performed in a fixed bed reactor reveal excellent values of activity and selectivity due to the highly dispersed Ni nanoparticles in the support surface. Time-on-stream behavior during 100 h operation in reaction conditions for sample N-NTO yield a stable CH4 conversion. Electrolyte supported symmetrical cells are prepared with both materials achieving excellent polarization resistance of 0.023 Ω cm2 in 7%H2/N2 atmosphere at 750 °C with sample N-NTO. The maximum power density achieved is of 273 mW cm−2 at 800 °C with a commercial Pt ink used as a reference cathode, indicating further improvement of the system can be achieved and positioning the N-NTO material as a promising SOFC anode material. |
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Support effects on catalysis of low temperature methane steam reforming
ID=577| Authors |
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RSC Adv.
Volume: 10,
Pages: 26418-26424 Time of Publication: 2020 |
| Abstract | Low temperature (<500 K) methane steam reforming in an electric field was investigated over various catalysts. To elucidate the factors governing catalytic activity, activity tests and various characterization methods were conducted over various oxides including CeO2, Nb2O5, and Ta2O5 as supports. Activities of Pd catalysts loaded on these oxides showed the order of CeO2 > Nb2O5 > Ta2O5. Surface proton conductivity has a key role for the activation of methane in an electric field. Proton hopping ability on the oxide surface was estimated using electrochemical impedance measurements. Proton transport ability on the oxide surface at 473 K was in the order of CeO2 > Nb2O5 > Ta2O5. The OH group amounts on the oxide surface were evaluated by measuring pyridine adsorption with and without H2O pretreatment. Results indicate that the surface OH group concentrations on the oxide surface were in the order of CeO2 > Nb2O5 > Ta2O5. These results demonstrate that the surface concentrations of OH groups are related to the proton hopping ability on the oxide surface. The concentrations reflect the catalytic activity of low-temperature methane steam reforming in the electric field. |
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Defects and polaronic electron transport in Fe2WO6
ID=576| Authors |
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Physical Chemistry Chemical Physics
Issue: 27
Time of Publication: 2020
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| Abstract | We report the synthesis of phase pure Fe2WO6 and its structural characterization by high quality synchrotron X-ray powder diffraction, followed by studies of electric and thermoelectric properties as a function of temperature (200–950 °C) and pO2 (1–10−3 bar). The results are shown to be in accordance with a defect chemical model comprising formation of oxygen vacancies and charge compensating electrons at high temperatures. The standard enthalpy and entropy of formation of an oxygen vacancy and two electrons in Fe2WO6 are found to be 113(5) kJ mol−1 and 41(5) J mol−1 K−1, respectively. Electrons residing as Fe2+ in the Fe3+ host structure act as charge carriers in a small polaron conducting manner. A freezing-in of oxygen vacancies below approximately 650 °C results in a region of constant charge carrier concentration, corresponding to an iron site fraction of XFe2+ ≅ 0.03. By decoupling of mobility from conductivity, we find a polaron hopping activation energy of 0.34(1) eV and a charge mobility pre-exponential u0 = 400(50) cm2 kV−1 s−1. We report thermal conductivity for the first time for Fe2WO6. The relatively high conductivity, large negative Seebeck coefficient and low thermal conductivity make Fe2WO6 an interesting candidate as an n-type thermoelectric in air, for which we report a maximum zT of 0.027 at 900 °C. |
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Tailoring the electrical conductivity and hardening in BiFeO3 ceramics
ID=575| Authors |
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Volume: 40,
Issue: 15,
Pages: 5483-5493 Time of Publication: 2020 |
| Abstract | In this report, the influence of cobalt doping and annealing atmosphere on the electrical conductivity and polarization switching of BiFeO3 (BFO) ceramics was studied. Electrical conductivity as well as hardening behavior has been found to increase with introduction of acceptor sites. BFO ceramics doped with Co exhibit p-type conductivity, dominated by Fe4+ defects, which can be successfully reduced during high-temperature annealing in N2. However, indications of local reduction were found, presumably on domain walls and grain boundaries. A mechanism of hardening is proposed, which assumes two types of pinning centers: i) and related and ii) and related, most probably bound into complexes, which are shown to play the key role in the hardening behavior and hysteresis loop pinching and biasing. The results of this study could further promote designing local and bulk conductivity and hardening properties of BFO-based materials. |
| Keywords | Ceramics; Ferroelectric; Point defects; Conductivity; Hardening |
| Remark | Link |
Disagreements between space charge models and grain boundary impedance data in yttrium-substituted barium zirconate
ID=574| Authors |
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Solid State Ionics
Volume: 353,
Pages: 115369 Time of Publication: 2020 |
| Abstract | Although the space charge model is commonly used to explain the high grain boundary resistance in proton conducting yttrium-substituted BaZrO3, it fails in its simplest forms with factors 10–40 to fit experimental data with respect to the characteristic frequency of the grain boundary impedance. We suggest modifications to the model, somewhat improving its fit. Including trapping effects of protons near yttrium substituents reduces the error only by factors less than 1.6. Increasing the width of the grain boundary core reduces the error with factors of 1.5–3. Discretizing the space charge layer, such that protons can only reside on specific, discrete sites, reduces the error with another factor of around 2. Considering reduced proton mobility in the GB by reducing its effective area may give a reduction in the fitting error of a factor of 2. Varying the dielectric constant in the GB does not affect the error considerably. Neither each single modification, nor their combined effect, can, however, account for the majority of the discrepancy between the space charge model and experimental data. |
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Insights into Crystal Structure and Diffusion of Biphasic Na2Zn2TeO6
ID=573| Authors |
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ACS Appl. Mater. Interfaces
Volume: 12,
Issue: 25,
Pages: 27821-28924 Time of Publication: 2020 |
| Abstract | The layered oxide Na2Zn2TeO6 is a fast Na+ ion conductor and a suitable candidate for application as a solid-state electrolyte. We present a detailed study on how synthesis temperature and Na-content affect the crystal structure and thus the Na+ ion conductivity of Na2Zn2TeO6. Furthermore, we report for the first time an O′3-type phase for Na2Zn2TeO6. At a synthesis temperature of 900 °C, we obtain a pure P2-type phase, providing peak performance in Na+ ion conductivity. Synthesis temperatures lower than 900 °C produce a series of mixed P2 and O′3-type phases. The O′3 structure can only be obtained as a pure phase by substituting Li on the Zn-sites to increase the Na-content. Thorough analysis of synchrotron data combined with computational modeling indicates that Li enters the Zn sites and, consequently, the amount of Na in the structure increases to balance the charge according to the formula Na2+xZn2–xLixTeO6 (x = 0.2–0.5). Impedance spectroscopy and computational modeling confirm that reducing the amount of the O′3-type phase enhances the Na+ ion mobility. |
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Ferroelectric Phase Transitions in Sr9Tm(VO4)7 upon Substitution of Calcium and Lead for Strontium
ID=572| Authors |
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Physics of the Solid State
Volume: 62,
Pages: 856–859 Time of Publication: 2020 |
| Abstract | In Sr9 – xMxTm(VO4)7 system, solid solutions with M = Ca (0 ≤ x ≤ 2) and M = Pb (0 ≤ x ≤ 1) have been prepared by solid-phase synthesis at 1373 K. At room temperature, the single-phase samples are isostructural to the Ca3(VO4)2 ferroelectric (space group R3c, Z = 6). The materials have been characterized by methods of the X-ray phase analysis (XPA), the second harmonic generation (SHG), and the dielectric spectroscopy. The intensity of the change in the SHG signal is changed within the range of 30–50 units with respect to a quartz standard in the dependence on cation–substitute and its concentration. A reversible ferroelectric phase transition is observed in the temperature range 850–960 K. The transition is accompanied by a sharp maximum in the curve of the dependence of the dielectric permittivity on temperature. The absence of the SHG signal at temperatures higher than the transition temperature indicates the centrosymmetricity of the paraelectric phase. |
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Electrochemical promotion of Ru nanoparticles deposited on a proton conductor electrolyte during CO2 hydrogenation
ID=571| Authors |
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Applied Catalysis B: Environmental
Volume: 276,
Pages: 119148 Time of Publication: 2020 |
| Abstract | Recycling CO2 into a carbon-neutral source is a beneficial approach in reducing non-renewable energy sources. Herein, the electrochemical promotion of catalysis (EPOC) has been exploited to enhance the catalytic activity of Ru nanoparticles (0.7−1¯nm) deposited on the proton conductor yttria-doped barium zirconate (BZY), as free-standing nanoparticles and supported on Co3O4 semiconductor, for CO2 hydrogenation. Under 250−450¯°C and atmospheric pressure, both methanation and reverse water-gas shift (RWGS) reaction take place simultaneously over the Ru nanoparticles with a superior selectivity to CO. Under anodic polarization, free-standing Ru nanoparticles displayed an increase in CH4 and a decrease in CO production, while the opposite effect was observed under cathodic polarization. Ru supported on Co3O4 displayed a superior catalytic activity mostly due to enhanced metal–support interactions. The electronic effects induced by the pairing of Co3O4 and BZY resulted in a new approach to EPOC applications that brings it closer to industrial application. |
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Ceramic-based thermoelectric generator processed via spray-coating and laser structuring
ID=570| Authors |
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Open Ceramics
Volume: 1,
Pages: 100002 Time of Publication: 2020 |
| Abstract | Processing technology to improve the manufacturing of thermoelectric generators (TEGs) is a growing field of research. In this paper, an adaptable and scalable process comprising spray-coating and laser structuring for fast and easy TEG manufacturing is presented. The developed process combines additive and subtractive processing technology towards an adaptable ceramic-based TEG, which is applicable at high temperatures and shows a high optimization potential. As a prototype, a TEG based on Ca3Co4O9 (CCO) and Ag on a ceramic substrate was prepared. Microstructural and thermoelectric characterization is shown, reaching up to 1.65 μW cm−2 at 673 K and a ΔT of 100 K. The high controllability of the developed process also enables adaptation for different kinds of thermoelectric materials. |
| Remark | Link |
Negative Thermal Expansion in Lead-Free La-Substituted Bi0.5Na0.5VO3
ID=569| Authors |
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Chem. Mater.
Volume: 32,
Issue: 11,
Pages: 4832–4837 Time of Publication: 2020 |
| Abstract | Negative thermal expansion (NTE) materials, which shrink upon heating, are required in modern technologies. In this study, new lead-free NTE compounds were obtained by substitution of La in PbTiO3 (PT)-type compounds, Bi0.5Na0.5VO3. Decreasing the stereochemical activity by substitution of La for Bi3+ and electron doping by substitution of La for Na+ were found to destabilize the tetragonal phase and cause a temperature-induced transition to a small cubic phase accompanied by NTE. The temperature hysteresis was suppressed because the phase transition was second order-like. |
| Remark | Link |
Studying the Effects of Siloxanes on Solid Oxide Fuel Cell Performance
ID=568| Authors |
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Time of Publication: 2020
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| Abstract | Solid oxide fuel cells (SOFCs) are a promising technology for converting landfill gas into electricity, simultaneously providing a renewable source of energy. However, the contaminants present in landfill gas pose an obstacle to using it for energy generation. The research objective was to examine the effect siloxanes in landfill gas have on the performance of Ni-YSZ/Hionic™/LSM SOFCs, particularly through silica deposition on the Ni-YSZ anode. This was accomplished with voltammetric experiments using the ProboStat™ and anode surface analysis using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). To establish whether siloxanes can be detrimental to SOFC operation, hydrogen spiked with varying concentrations of decamethylcyclopentasiloxane (D5), a representative siloxane, was used as a fuel gas. Compared to operation under pure H2, which reliably gives a steady state output, the cell showed a 10% loss in voltage after 3 hours each at 1 ppmv D5 and 5 ppmv D5. Another cell operated on H2 gas containing 10 ppmv D5 experienced a 13% loss in voltage output after 6 hours, and SEM/EDS analysis showed the presence of silica deposits on the cell anodes. This was viewed as water generated via electrochemical reaction hydrolyzing siloxanes to silica and poisoning the SOFC anode. However, when humidified methane, a better landfill gas analogue, was spiked with D5, the cell’s voltage output was stable, and silica was not detected on the anode; instead D5 was deposited as silica on surfaces inside the ProboStat™. Thus, the necessity of humidifying the hydrocarbon fuel also provided a protection against anode poisoning by siloxanes. Nevertheless, experiments with humidified Mahoning Landfill gas failed to reach the expected voltage and current output. It was not clear from SEM/EDS analysis what contaminants were responsible for the decreased cell performance; more surface-sensitive techniques are recommended for further studies. |
| Remark |
Master of Science in Chemistry, Youngstown State University, Department of Chemistry. Link |
High ionic conductivity dysprosium and tantalum Co-doped bismuth oxide electrolyte for low-temperature SOFCs
ID=567| Authors |
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| Source |
Ionics
Volume: 26,
Pages: 4579–4586 Time of Publication: 2020 |
| Abstract | A novel double dysprosium- and tantalum-doped bismuth oxide electrolyte synthesized by solid-state reaction for low-temperature solid oxide fuel cells (LT-SOFCs) is here reported. The phase structures at room temperature were defined by X-ray powder diffraction (XRD). A stable δ-Bi2O3 phase was obtained by co-doping Bi2O3 with Dy2O3 and Ta2O5 in specific contents. The effect of the co-dopant total content (5–15 mol%) on the ionic conductivity was measured as a function of temperature (300 to 700 °C). Results revealed that the (Dy2O3)13(Ta2O5)2(Bi2O3)85 system showed the highest ionic conductivity as 0.08 S cm−1 at 500 °C, which is three times higher than the binary system reported in the literature (E2O3)20(Bi2O3)80 (20ESB) and in the same range as the ternary system with the highest conductivity reported so far (Dy2O3)8(W2O3)4(Bi2O3)88 (8D4WSB). The lowest activation energy for our system was 0.20 eV at temperatures higher than 550 °C. |
| Remark | Link |
Ruddlesden-Popper-type Nd2-xNi1-yCuyO4±δ layered oxides as candidate materials for MIEC-type ceramic membranes
ID=566| Authors |
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| Source |
Journal of the European Ceramic Society
Volume: 40,
Issue: 12,
Pages: 4056-4066 Time of Publication: 2020 |
| Abstract | Series of Nd2-xNi1-yCuyO4±δ Ruddlesden-Popper-type oxides is obtained by auto-combustion synthesis method and systematically characterized concerning phase composition, formation of solid state solution, crystal structure, oxygen content, as well as regarding transport properties and oxygen permeability when applied as mixed conducting ceramic membranes. The A-site deficiency x is discussed in terms of structural stability and its effect on the oxygen content, with ongoing modification of total electrical conductivity observed. In selected Nd2-xNi0.75Cu0.25O4±δ oxides the dominating oxygen defects at high temperatures can be changed from oxygen interstitials to vacancies by the induced A-site deficiency, which affects bulk- and surface-related transport coefficients, as it is observed in electrical conductivity relaxation studies. The optimized Nd1.9Ni0.75Cu0.25O4±δ sinters having increased ionic conductivity, as well as fine, well-sintered microstructure allow to achieve one of the higher reported oxygen fluxes for CO2-stable Ruddlesden-Popper-based ceramic membranes (e.g. 0.49¯mL¯cm−2¯min−1 at ca. 880¯°C for 1.05¯mm thickness). |
| Keywords | Ruddlesden-Popper oxides, Nonstoichiometric compounds, Crystal structure, Transport properties, Oxygen permeation membranes |
| Remark |
https://doi.org/10.1016/j.jeurceramsoc.2020.04.054 Link |
Artificial photosynthesisAdvanced nanomaterials and use of biocatalystsfor novel photoelectrochemical cells
ID=565| Author |
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| Source |
Time of Publication: 2020
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| Remark |
Thesis submitted for the degree of Philosophiae Doctor, University of Oslo Link |
