The intrinsic origin of the grain-boundary resistance in Sr-doped LaGaO3

Abstract  

In this paper I summarize our recent investigations (Park and Kim, Phys Chem C 111:14903, 2007; Solid State Ionics 179:1329, 2008) on the origin of the grain-boundary resistance in a doped LaGaO₃, a perovskite-structured solid electrolyte. The partial electronic and ionic resistances of the bulk and the grain boundaries, as well as the total resistance, in 1 mol% Sr-doped LaGaO₃ were measured separately by means of a dc-polarization method and ac-impedance spectroscopy. Both of the partial resistances at the grain boundaries were greater than the bulk counterparts, indicating that the grain boundaries impede the ionic as well as the electronic transport in this material. The transference number of the partial electronic conductivity at the grain boundary was however greater than that in the bulk. This fact strongly suggests that both electronic and ionic charge carriers deplete at the grain boundaries to form the space-charge zones and that the grain-boundary cores in this material are positively charged. In light of the fact that the effective charge of the oxygen vacancy (+2) is greater than that of the electron hole (+1), the oxygen vacancies deplete more sharply in the space-charge zones compared to the electron holes such that the grain boundaries become more mixed conducting relative to the bulk. These observations verify that the electrical conduction across the grain-boundaries in 1 mol% Sr-doped LaGaO₃ is governed by the space charge.     

An atomistic simulation study of oxygen-vacancy migration in perovskite electrolytes based on LaGaO3

Abstract  Static lattice simulation techniques were used to calculate the energetic barriers for oxygen-vacancy migration in the perovskite-type oxide LaGaO₃ substituted with alkaline earth cations. The calculated migration energies are found to vary with the number and size of the substituting cations in the immediate neigbourhood of the migrating defect. It is argued that not only the size but also the charge of the cations constituting the saddle-point configuration play a role in determining the migration energy. Graphical abstract        

Structure and conductivity in CeNb<Subscript>3</Subscript>O<Subscript>9-δ</Subscript>

Abstract  In the search of new materials for solid oxide fuel cells, a study of the structure and electrical conductivity of Mg-doped and nominally pure CeNb₃O_9-δ was undertaken. This material exhibits an orthorhombic crystal structure as determined by Rietveld refinement. Through a combined study of 4-point DC and AC impedance spectroscopy, it was determined that the material presents oxygen ion conductivity, electron conductivity and electron-hole conductivity according to the partial pressure of oxygen and temperature in agreement with a simple defect chemistry model. Finally, some experiments seem to indicate the presence of proton conduction. Graphical Abstract        

A highly efficient and ecofriendly procedure for tetrahydropyranylation of alcohols and phenols in the presence of in-situ generated I2 under heterogeneous and neutral conditions

Abstract  Molecular iodine generated in situ from Fe(NO₃)₃·9H₂O/NaI acts as a highly efficient catalyst for tetrahydropyranylation of various alcohols and phenols with 3,4-dihydro-2H-pyran in almost quantitative yields. The reaction occurs rapidly in dichloromethane at room temperature, and use of toxic molecular iodine is avoided. Graphical Abstract        

Very fast and efficient synthesis of some novel substituted 2-arylbenzimidazoles in water using ZrOCl2·nH2O on montmorillonite K10 as catalyst

Abstract  A simple and eco-friendly protocol for the synthesis of some novel substituted 2-arylbenzimidazoles was developed. In this process, these compounds were prepared in water as the solvent using ZrOCl₂·nH₂O supported on montmorillonite K10 as an efficient water tolerating Lewis acid. The reaction was performed under mild conditions with good to excellent yields and remarkable chemoselectivity in the absence of any byproduct. Graphical Abstract        

An efficient and convenient protocol for the synthesis of novel 1′H-spiro[isoindoline-1,2′-quinazoline]-3,4′(3′H)-dione derivatives

Abstract  An efficient and direct procedure for the synthesis of novel spiro[isoindoline-1,2′-quinazoline]-3,4′(3′H)-dione derivatives is described. The process employs a condensation reaction of 2-aminobenzamides and isatins in the presence of a catalytic amount of KAl(SO₄)₂.12H₂O (alum) in ethanol under reflux. Graphical Abstract        

Influence of interface structure on mass transport in phase boundaries between different ionic materials

Abstract  Internal and external interfaces in solids exhibit completely different transport properties compared to the bulk. Transport parallel to grain or phase boundaries is usually strongly enhanced. Transport perpendicular to an interface is usually blocked, i.e., transport across an interface is often much slower. Due to the high density of interfaces in modern micro- and nanoscaled devices, a severe influence on the total transport properties can be expected. In contrast to diffusion in metal grain boundaries, transport phenomena in boundaries of ionic materials are still less understood. The specific transport properties along metal grain boundaries are explained by structural factors like packing densities or dislocation densities in the interface region. In most studies dealing with ionic materials, the interfacial transport properties are merely explained by the influence of space charge regions. In this study the influence of the interface structure on the interfacial transport properties of ionic materials is discussed in analogy to metallic materials. A qualitative model based on the density of misfit dislocations and on interfacial strain is introduced for (untilted and untwisted) phase boundaries. For experimental verification, the interfacial ionic conductivity of different multilayer systems consisting of stabilised ZrO₂ and an insulating oxide is investigated as a funtion of structural mismatch. As predicted by the model, the interfacial conductivity increases when the lattice mismatch is increased. Graphical abstract  

Square-planar mixed ligand nickel dithiolenes as second-order non-linear chromophores: synthesis and characterisation of [Ni(Me<Subscript>2</Subscript>pipdt)(dddt)]

Abstract  The novel [Ni(Me₂pipdt)(dddt)] complex based on the Me₂pipdt (1,4-dimethylpiperazine-3,2-dithione) and dddt (5,6-dihydro-1,4-dithine-2,3-dithiolate) ligands has been synthesised and characterised. Structural data, vibrational marker, solvatochromic behaviour of the typical absorption in the near infrared region, and approximate theoretical calculations suggest that an unbalanced electron distribution at the dithiolene core occurs in the ground and excited states. In particular, the dddt ligand gives a prevailing contribution to the HOMO, and Me₂pipdt to the LUMO. The charge-transfer character of the HOMO–LUMO transition makes this complex a potential second-order non-linear optic chromophore. Graphical Abstract        

A synthesis of diethyl alkylsulfanylmethylmalonates catalyzed by KOH in an ionic liquid

Abstract  1-Ethyl-3-methylimidazolium bromide was used as a green recyclable alternative to volatile organic solvents for KOH catalyzed three-component synthesis of diethyl alkylsulfanylmethylmalonates from aldehydes, diethyl malonate, and alkylthiols. Graphical Abstract  A synthesis of diethyl alkylsulfanylmethylmalonates catalyzed by KOH in an ionic liquid      

The impedance caused by interfacial current constriction: a case study on BaF<Subscript>2</Subscript>/YSZ bicrystals

Abstract  BaF₂/YSZ (yttria stabilized zirconia) bicrystals are investigated by means of impedance spectroscopy. The spectra show two semicircles in the complex impedance plane, and both arcs exhibit very similar temperature dependences. The high frequency semicircle can be attributed to the ideal (quasi one-dimensional) bulk resistance of BaF₂, and the low frequency arc is caused by an additional resistance in BaF₂ due to the current constriction taking place close to the contact spots at the imperfect bicrystal interface. This interpretation is supported by finite element calculations revealing that bicrystals with imperfect contacts indeed exhibit an additional semicircle in the complex impedance plane even without any ion transfer resistance between the two crystals. The low frequency arc of the BaF₂/YSZ bicrystal drastically increases upon bias voltage, but relaxes to its original value after removing the bias. This phenomenon can be associated with a strong decrease of the vacancy concentration in YSZ (close to the interfacial contact spots), which is caused by F⁻ ions being pumped into YSZ and acting as a counter dopant to Y³⁺. Graphical Abstract        

Generalized equivalent circuits for mixed conductors: silver sulfide as a model system

Abstract  The generalized equivalent circuit for Hebb–Wagner polarization in the frequency domain proposed by Jamnik and Maier (J Electrochem Soc 146:4183, 1999) includes the space-charge polarization that was previously neglected. In the present work, using a self-coded Fortran program, the completely generalized equivalent circuit is successfully applied to a mixed conducting silver sulfide with an AgI electrode that suppresses the electronic flow. A whole set of fit parameters, such as geometric capacitance, partial conductivities, chemical capacitance or diffusivity, and the blocking and shunting characteristics of electrodes are independently but self-consistently obtained over a range of silver activities, as controlled by a galvanic cell. The interfacial capacitance was found to be much larger than the diffuse space-charge double-layer capacitance and was thus ascribed to the adsorption capacitance at the core of the interface, which should be connected in parallel with the space-charge double-layer polarization. Two simplified equivalent circuits were shown to be good approximations for the spectra at the extreme low and high silver activity, respectively. Graphical abstract   It was belatedly learned that Derek Johnson, Scribner Ass. Inc., has implemented a “Jamink+Maier/Mixed Conductor” model in Zview 3.1.     

Practical and general method for the direct synthesis of alkyl fluorides from alcohols under mild conditions: a reinvestigation

Abstract  In contrast to the results presented in a previous report, the direct conversion of alcohols to alkyl fluorides with triphenylphosphine and potassium fluoride in CCl₄/DMF under mild conditions failed. Graphical Abstract        

DFT study on the preactivation reaction of a palladium catalyst precursor in phosphine-free Heck reactions

Abstract  The mechanism of the preactivation process of trans-dichlorobis(diethanolamine-N)palladium(II) complex is investigated using density functional theory. The role of diethanolamine (a solvent for the reaction in the absence of a strong base) and acetonitrile (solvent for the reaction in the presence of a strong base) is analyzed by using a discrete model. The Onsager model is applied to assess the effect of the bulk medium. Both models show that diethanolamine activates the complex and thus is a better suited solvent for the Heck reactions of the investigated complex. Graphical abstract        

Microstructure and electrical properties of aluminium-substituted La(Sr)Ga(Mg)O3–δ-based solid electrolytes

Abstract  A study of the influence of the substitution of Al for Ga in the ceramic processing and electrical properties of La_0.95Sr_0.05Ga_0.90–x Al _x Mg_0.10O_3–δ (0 ≤ x ≤ 0.3) solid electrolytes is presented. The materials retained orthorhombic symmetry over the entire substitution range, whereas a deviation from Vegard’s law for x > 0.20 suggested a maximum Al solubility of x = 0.20. Scanning electron microscopy analysis of ceramic samples revealed that grain growth was inhibited for x ≥ 0.2. This microstructural change was related to an apparent deterioration of mechanical properties, as suggested by room-temperature Vickers hardness measurements. Impedance spectroscopy revealed a significant degradation of the grain-boundary electrical properties for x ≥ 0.20, whereas the bulk conductivity was enhanced for 0.10 ≤ x ≤ 0.15. Oxygen-permeability measurements confirmed that the studied materials remain essentially pure ionic conductors. An ionic conductivity maximum of 0.047 S/cm at 700 °C was obtained for x = 0.10. The effect of aluminium in the grain-bulk ionic conductivity is discussed in terms of defect cluster models and assuming fast oxygen diffusion along domain walls. Graphical Abstract        

A diol-functionalized ionic liquid: an efficient, simple, and recoverable “capture and release” reagent for aldehydes

Abstract  A new diol-functionalized ionic liquid, 2,2-bis(1-(1-methylimidazolium)methylpropane-1,3-diol hexafluorophosphate, was synthesized and applied as a facile, efficient, and recoverable “capture and release” reagent for aldehydes. This method has the advantages of homogeneous reaction, heterogeneous separation, and recyclable uses. Graphical abstract        

Application of various ionic liquids as cosolvents for chloroperoxidase-catalysed biotransformations

Abstract  Chloroperoxidase from Caldariomyces fumago catalyses oxidation of indole and thioanisole in reaction mixtures containing up to 40% (v/v) of different ionic liquids (ILs). Results indicate that ILs containing tosylate, trifluoroacetate, chloride, and methylsulfate anions are suitable cosolvents for these transformations, yielding high enantiomeric excess and good conversion rates. Graphical abstract       

Fluorescent probe for Zn<Superscript>2+</Superscript> with light-harvesting pyrenyl groups: sensitization via intramolecular energy transfer

Abstract  Bis[N-(1-pyrenylmethyl)salicylideneaminato]zinc(II) emits intense fluorescence on excitation of the pyrenyl group. This fluorescence originates from the excited state of the salicylideneamine moiety, indicating that efficient intramolecular energy transfer takes place. The occurrence of such efficient energy transfer is accounted for by significant spectral overlap between the emission from the S₁ state of the pyrenyl group and the absorption of the salicylideneamine–zinc complex. Graphical abstract        

Amino acid derivatives, X [1]: synthesis and antimicrobial evaluation of α-amino acid esters bearing a N1-protected tryptophan side chain

Abstract  A series of peptide derivatives conjugated with N¹-protected tryptophan residue was synthesized. The prepared compounds were tested for antimicrobial activity against four different bacterial species displaying different degrees of antibacterial activities or inhibitory actions. Graphical Abstract        

Efficient conversion of aldoximes to nitriles using phosphoric acid diethyl ester 2-phenylbenzimidazol-1-yl ester

Abstract  Aromatic aldoximes were converted to the corresponding nitriles in good to excellent yields by employing phosphoric acid diethyl ester 2-phenylbenzimidazol-1-yl ester as reagent. The method was equally effective for oximes bearing electron-donating and electron-withdrawing substituents. Graphical Abstract        

Synthesis and pharmacological activity of some synthesized polyazacyclopenta[<Emphasis Type="Italic">a</Emphasis>]naphthalenes and pyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]pyridines using 2-amino-6-methyl-4-phenylnicotinonitrile as synthon

Abstract  A series of pyridines, pyrimidines, and their derivatives were synthesized using 2-amino-6-methyl-4-phenylnicotinonitrile as starting material. Thirteen new heterocyclics containing a pyridine ring were thus prepared. Pharmacological screening showed that many of these compounds have good anti-inflammatory and analgesic activity comparable with those of diclofenac potassium and valdecoxib as reference drugs. Assignment of the structures of the new compounds was based on chemical and spectroscopic evidence. Synthesis, spectroscopic data, and pharmacological properties of the compounds are reported in detail. Graphical Abstract