Top PDF Defect chemistry and proton conductivity in Ba-based perovskites

Defect chemistry and proton conductivity in Ba-based perovskites

Defect chemistry and proton conductivity in Ba-based perovskites

As we mentioned earlier in Fig. 3-3, the variation in cell vomume with Ba content implies that there is some compositional range, Ba:(Ce+M), over which the perovskite phase exists, and that this range is dependent on the specific dopant. The observation of a composition independent lattice constant for Yb doped samples (with the exception of one apparently anomalous data point) is consistent with a perovskite phase of fixed stoichiometry, and almost no Yb on the A-site. This is consistent with the fact that ceria precipitates were observed for the Yb doped, barium deficient samples. In contrast, the Gd, Sm, Nd and, to some extent, the La-doped samples show measurable dependence of the cell volumes on stoichiometry, consistent with the presence of a single phase of variable composition. The increase in volume with increasing barium content is furthermore consistent with the increasing concentration of dopant on the B-site. The trends obtained from the two types of samples, solid state reaction synthesized and chemical route synthesized, are similar, but the absolute values of the cell volumes are measurably different. The different processing routes likely yield samples with different final barium contents. Similarly, the slight site incorporation difference between calcined and sintered samples listed in Table 3-3 may be attributable to the loss of Ba at high processing temperature.
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Modified strontium titanates : from defect chemistry to SOFC anodes

Modified strontium titanates : from defect chemistry to SOFC anodes

Figure 14 shows the changes of OCV and performance at 0.7 V, of the cell as a function of the numbers of redox cycles. Impressively, after 200 redox cycles, the OCV only decreased by 1.3%, indicating the high robustness and stability of the cell. In contrast, state-of-the-art SOFCs based on Ni cermets usually collapsed, or had apparent losses of OCV after just one redox cycle 9 . However, the performance of the cell decreased by 35% after 200 redox cycles. The reason is most likely the gradual loss of electrical conductivity after each redox cycle either due to an irreversible decrease of charge carriers, or due to the slow kinetics between the reduced and oxidized state of YST materials. As previously mentioned, the conductivity of YST sintered in reducing atmosphere, as well as other SrTiO 3 based materials, depends
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The defect chemistry of pyrochlore structured oxides

The defect chemistry of pyrochlore structured oxides

The measurements on which the simulations in this thesis are largely based (Moon 1980) were made on polycrystalline samples and so it is first necessary to distinguish between the contributions made to the total conductivity by the separate electrical process such as bulk, grain-boundary and electrode impedance. These have different characteristic time constants and may be separated using complex impedance spectroscopy, which measures frequency dependent electrical impedance. The underlying theory involved in modelling this technique is described in a paper by Bauerle (1969). Data on impedances for the conventional model of a polycrystalline ceramic can be represented as a series of semicircles in a plot of real against imaginary impedance and the plots obtained for the pyrochlore samples measured by Moon correspond well to this pattern with little overlap of the different arches. The bulk resistance (from which the total bulk conductivity is calculated), corresponds to the intercept of one of these semicircles with the real impedance axis and so it is possible to determine this value accurately and unambiguously.
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AB-INITIO STUDY OF BULK MODULUS AND CHARGE DENSITY OF CUBIC SrMO 3

AB-INITIO STUDY OF BULK MODULUS AND CHARGE DENSITY OF CUBIC SrMO 3

material for various uses incorporating a number of perovskite-based ferroelectric, dielectric, and conductive films. Yet, numerous studies have shown that this is no longer the case for some promising TMO such as ruthenates and molybdates. These oxides are observed to exhibit unconventional superconductivity [8] and research is going on to understand the mechanism [9] of this new quantum order due to strong electron-electron interaction. In addition to this, non-Fermi liquid behavior has been observed in SrRuO 3 [10]. Pseudo gap

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The defect chemistry of UO2±x from atomistic simulations

The defect chemistry of UO2±x from atomistic simulations

in supercells sufficiently large for the calculation of accurate defect energies. Therefore, spin-polarization with a 1-k antiferromagnetic ordering has been used to provide a reasonable description of the lowest en- ergy ordering. Spin orbit coupling has been shown to be over an order of magnitude weaker than coulombic interactions in 5f systems [54] justifying the use of 1-k antiferromagnetic ordering. A 500 eV plane-wave cut-off energy was used. A 2 × 2 × 2 Monkhorst-Pack k-point mesh [55] was used for k space integration with Gaussian smearing of 0.05 eV.

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High Performance CsPbI2Br Perovskite Solar Cells with Zinc and Manganese Doping

High Performance CsPbI2Br Perovskite Solar Cells with Zinc and Manganese Doping

Hybrid organic–inorganic perovskites have aroused great concerns because of their excellent electronic and op- tical properties [1–7] such as high mobility of the charge carriers and tunable band gap [8–11]. Notably, the power conversion efficiency (PCE) of perovskite-based organic–inorganic hybrid solar cells has improved from 3.8 to 23.3% through the cation exchange [12–17]. There are still challenges to overcome all environmental deg- radation [18]. Up to now, the cesium lead halide per- ovskite solar cells have been researched by many groups [19–22]. The large band gap of CsPbBr 3 is about 2.3 eV,
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Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates

Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates

Rare earth metal phosphates have been of particular interest to the potential applications in fuel cells, gas sensors and ceramic membranes due to their superior thermal and chemical stability. Recent research has been devoted to exploration of the proton conductivity as potential electrolyte materials for intermediate temperature fuel cells and other electrochemical systems [1,2]. The rare earth metal phosphates exist in nature as monoclinic monazite and tetragonal xenotime. The formula is in both cases MPO 4 , but monazite preferentially incorporates mixtures of larger rare earth elements from La to
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Interfaces, Defect Chemistry, and Resistance Degradation of Dielectric Titanates.

Interfaces, Defect Chemistry, and Resistance Degradation of Dielectric Titanates.

When ionic drift occurs in a system with ionically blocking electrodes (red line in figure 2.4) the result is macroscopic ionic de-mixing of the defects[64, 17, 73, 9, 74, 22, 44, 72, 62, 75] which, in some cases, can lead to significant non-stoichiometry.[64, 60, 76] De-mixing is the process of polarizing defect concentrations, with some regions becoming depleted and others becoming enhanced with that defect species. The system becomes more complex when one of the electrodes are partially or fully permeable to ion transfer. Permeable interfaces will equilibrate with the environment, acting as a source or sink for the defect population at the electrode interface.[72] The steady state (t = ∞) ionic current density still goes to zero, leading to the same concentration gradient with the caveat that the permeable electrode maintains equilibrium with the gas phase which can leads to a net oxidation (green) or net reduction (blue) of the system. When the ionic flux is significant at both terminal electrodes the system is said to be fully ionically permeable, and does not undergo ionic de-mixing (a key challenge of solid oxide fuel cell operation).[31, 32, 77] In some cases the electrode is ionically blocking but the dielectric allows ions to flux anyway. When this happens, oxygen expression can force oxygen gas underneath[78] or into the electrode’s grain boundaries[29, 30] and cause a net reduction of the dielectric.
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Effect of adding Nanoclay (Cloisite-30B) on the Proton Conductivity of Sulfonated Polybenzimidazole

Effect of adding Nanoclay (Cloisite-30B) on the Proton Conductivity of Sulfonated Polybenzimidazole

A novel sulfonated polybenzimidazole/organoclay (Cloisite-30B) (SPBI/clay) nanocomposite membranes was successfully synthesized based on aromatic diacide (1) and diaminobenzidine. Nanocomposite membranes were fabricated using 1, 4-bis (hydroxymethyl) benzene (BHMB) as cross-linker, and Cloisite-30B organoclay as the pseudo cross-linker. The cross-linked SPBI/clay nanocomposite membranes were prepared via solution intercalation method. Participation of reactive organoclay in the cross-linking process was established from ion exchange capacity (IEC) measurements and FTIR studies. Wide angle X-ray diffraction (WAXD), field emission-scanning electron microscopy (FE- SEM), and transmission electron microscopy (TEM) techniques confirmed the presence of a combination of the intercalated and partially exfoliated clay platelets in the cross-linked SPBI/clay nanocomposite membrane. The cross- linked SPBI/clay nanocomposite membranes showed higher tensile strength, modulus and lower elongation at break compared to neat cross-linked SPBI. Water and methanol uptake studies revealed superior barrier properties of cross-linked SPBI/clay nanocomposite membranes compared to cross-linked SPBI. Furthermore, thermal stability, residual solvent in the membrane film, and structural ruination of membranes were analyzed by thermal gravimetric analysis (TGA). TGA data indicated an increase in thermal stability of the SPBI/ clay nanocomposite membranes compared to the pure polymer. The oxidative stability of SPBI improved remarkably with cross-linking and subsequent clay addition. These improvements in the thermo-mechanical, barrier and oxidative stability of the membranes could be achieved without significantly affecting the protonic conductivity.
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Field-induced Point Defect Redistribution in Metal Oxides: Mesoscopic Length Scale Phenomena.

Field-induced Point Defect Redistribution in Metal Oxides: Mesoscopic Length Scale Phenomena.

The spatial redistribution of charged point defects under direct-current (DC) biasing can have significant implications for electroceramic device performance and lifetime. The transport behavior of point defects is regulated by the boundary conditions of the electrodes, which can block electronic charge and/or ion transfer across the interface to varying degrees. When the electrodes are impermeable to mass transport, there will be an accumulation of point defects in the near-electrode region that can lead to significant modifications in the local electronic carrier concentrations. Such defect redistribution is responsible for the long- term increases in leakage current in many capacitor devices via modification of the interface Schottky barrier at the reverse-biased cathode.
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Synthesis and Topochemical Manipulation of New Layered Perovskites

Synthesis and Topochemical Manipulation of New Layered Perovskites

was pressed into pellets using a hand press (Sigma Aldrich), sealed under vacuum in a Pyrex tube, and heated at 350 °C for 3 days. The products were washed with copious amounts of hot water to remove unreacted starting material and rubidium by-products, rinsed with acetone, and dried overnight at 100 °C. Efforts were made to obtain the proton and sodium analogues; while preliminary results showed evidence for ion exchange based on the shift of the first reflection towards higher angles along with a change in the overall pattern, the resulting compounds were poorly crystalline.
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New Dion-Jacobson and Ruddlesden- Popper Layered Perovskites prepared by Topochemical Methods

New Dion-Jacobson and Ruddlesden- Popper Layered Perovskites prepared by Topochemical Methods

found by Fukuoka and co-workers to exhibit superconductivity on doping with lithium. 4 A further feature of ion-exchangeable layered perovskites is their ability to readily undergo topochemical reactions under relatively low temperatures (<500 °C). This chemistry can be used for the preparation of low temperature and metastable phases, 1 producing compounds typically not accessible by standard high temperature ceramic techniques. Reaction methods are varied and include ion exchange, intercalation, de-intercalation, grafting, etc. One focus in this topochemistry has been the effort by some researchers to form metal-nonmetal layers within the perovskite hosts. This has resulted in the construction of both transition metal and alkali-metal halide arrays. The co-exchange of cation and anion species for example can be used to build transition metal halide layers (e.g. Cu−Cl in (CuCl)LaNb 2 O 7 ). 5 A three-step method involving
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Effects of Freezing and Thawing on the Structures of Porous Gas Diffusion Media in PEM Fuel Cells

Effects of Freezing and Thawing on the Structures of Porous Gas Diffusion Media in PEM Fuel Cells

degradation Cho and the attributes the environmental chamber that temperature for current and voltage the current and proton of density at conductivity the fuel cell, as behavior 0.6 vol[r]

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Curie-Temperature Variation and Microwave Absorption in Perovskites Containing Substitutional Impurities

Curie-Temperature Variation and Microwave Absorption in Perovskites Containing Substitutional Impurities

It is easy to control the dielectric properties of BST (Ba x Sr 1-x TiO 3 ) by adjusting [Ba]/[Sr] ratio. The Curie-temperature of BT shifts below room temperature with increasing Sr contents thus making BST a paraelectric with low microwave loss at room temperature 11 . For bulk Ba

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Preparation and Characterization of UV Irradiated SPEEK/Chitosan Membranes

Preparation and Characterization of UV Irradiated SPEEK/Chitosan Membranes

The major function of the membrane can be classified as: i) a proton conductor, ii) a fuel barrier and iii) a mechanical separator between the anode and cathode [6]. Sulfonated polymembrane such as SPEEK is most promising candidate as an alternative to Nafion membrane because it is cheap, possesses good mechanical properties and high thermal stability. However the highly sulfonated membrane tends to swell excessively under the humidified conditions and lose their dimensional stability [7].

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Perovskite Solar Cells

Perovskite Solar Cells

While major challenges indeed exist, perovskite solar cells are still touted as the PV technology of the future, and much development work and research are put into making this a reality. Scientists and companies are working towards increasing efficiency and stability, prolonging lifetime and replacing toxic materials with safer ones. Researchers are also looking at the benefits of combining perovskites with other technologies, like silicon for example, to create what is referred to as “tandem cells”.

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Synthesis of Electroconducting Hydroxy Sodalite/Graphite Composite: Preparation and Characterization

Synthesis of Electroconducting Hydroxy Sodalite/Graphite Composite: Preparation and Characterization

Electroconductive hydroxy-sodalite/graphite composites were successfully syn- thesized by alkali-activation of Jordanian or pure kaolinite clay (JK and PK, re- spectively) in the presence of graphite as a conductive phase. The X-ray diffrac- tion results demonstrated that the intercalation of conducting graphite materials with JK or PK layers occurred in the composite structure formation. The FTIR study also showed the successful incorporation of graphite in the clay structure. The electrical conductivity of the composites increased with the increase in gra- phite percentage in the composite.
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Technical note: Continuous fluorescence based monitoring of seawater pH in situ

Technical note: Continuous fluorescence based monitoring of seawater pH in situ

from 100 min of consecutive measurements during each de- ployment) was 0.009 and 0.007 pH units for the April and December deployments, respectively. The best precision can be achieved by averaging multiple measurements, although this will of course hide real variability. Gradual bleaching is known to influence fluorophores (Lakowicz, 2006), con- tributing to a steady drift. This was accounted for with cor- rections based on samples collected in situ as described above. In this case, the decline in pH was 0.0136 pH units per day which is approximately 3 times the drift associ- ated with measurement-induced bleaching of 0.003 pH units per 1000 measuring points as stated by the manufacturer. The pH measured over summer ranged from 7.95 to almost 8.15 units, some 0.1 units more basic than autumn values (Fig. 5).
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Experimental and Kinetic Study of CO Oxidation Over LaFe1-xCuxO3 (x=0, 0.2, 0.4, 0.6) Perovskite-Type Oxides

Experimental and Kinetic Study of CO Oxidation Over LaFe1-xCuxO3 (x=0, 0.2, 0.4, 0.6) Perovskite-Type Oxides

CO was achieved at 275 ºC with this catalyst. Kinetic studies for CO oxidation were performed based on power law and Mars-van Krevelen mechanisms. According to kinetic calculations, the most probable mechanism is the MKV-D (dissociative adsorption of oxygen) which can predict the experimental data with correlation coefficient of R 2 > 0.995.

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Computational analysis of the defect chemistry of ceria

Computational analysis of the defect chemistry of ceria

To test whether La-doped Ce02 would bo effective for catalysing oxidation/nxluction reactions, first principle energetics were used to determine the energy required to oxi­ dise CO to CO[r]

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