Search results for "ionic"
showing 10 items of 2016 documents
<title>Optical characteristics of doped lithium niobate single crystals</title>
2003
Studing of the Raman spectra was established that an optical parameters of oxygen-polyhedral ferroelectric single crystals can be improved by increasing the degree of structural ordering of the cation sublattice along the polar axis by doping them. In this case the impurity ions with the ionic radii close to the radii of the main cations (Li+ and Nb5+) and charges intermediate between those of main cations (1<Z<5) in the area of rather low concentrations were shown to exert an ordering effect on the cation sublattice of a congruent lithium niobate single crystals. Moreover the crystal resistance to laser radiation is also observed to grow. It was determined that the effect of diminishing ph…
Dopants and defects: local structure and dynamics in barium cerates and zirconates
2010
In this paper we present an overview of state-of-the-art EXAFS measurements and data analysis on Ba, Ce, Zr, Y, In and Gd local environments in Y:BaCeO3, In:BaCeO3, Gd:BaCeO3, Y:BaZrO3, and In:BaZrO3, at different temperatures, hydration degrees and doping levels. This approach allows to reach unprecedented insights on the peculiar role of the dopant, and its interactions with the other lattice defects. In particular, we evidence that each different dopant shows unique behavior, depending mainly on its electronic structure, and that the usual criterion of ionic radius matching is not useful to outline an effective doping strategy of proton-conducting perovskites. As what concerns the struct…
Impact of point defects on the elastic properties of BaZrO3: Comprehensive insight from experiments and ab initio calculations
2018
Abstract Acceptor doped BaZrO3 is the prototype of proton conducting perovskites which are of strong interest as electrolytes for intermediate temperature fuel cells. Elastic properties of both dry and hydrated Y-doped BaZrO3 (1.5–17 mol% Y) were determined using ultrasound time of flight (TOF) measurements, and complemented by ab initio calculations which allow for an analysis of the different contributions. The experimental and theoretical findings are consistent and reveal a strong decrease of the Young's, shear and bulk moduli upon increasing dopant concentration. This decrease is attributed to a combined effect of (i) macroscopic lattice chemical expansion mainly caused by differing io…
Efficient light-emitting electrochemical cells using small molecular weight, ionic, host-guest systems
2015
This work has been supported by the Spanish Ministry of Economy and Competitiveness (MAT2014-55200). Light-emitting electrochemical cells (LECs) based on fluorescent host-guest small molecules system are reported. The LECs show electroluminescence coming solely from the guest, with an external quantum efficiency (EQE) of 2.0%, which is very close to the theoretical maximum EQE (2.2%) for this particular system. This work demonstrates the possibility to obtain high efficiency devices employing low-cost materials, making host-guest systems a real alternative to more traditional semiconducting polymer or transition metal compounds. Postprint Peer reviewed
Kinetic Ionic Permeation and Interfacial Doping of Supported Graphene
2019
Due to its outstanding electrical properties and chemical stability, graphene finds widespread use in various electrochemical applications. Although the presence of electrolytes strongly affects its electrical conductivity, the underlying mechanism has remained elusive. Here, we employ terahertz spectroscopy as a contact-free means to investigate the impact of ubiquitous cations (Li+, Na+, K+, and Ca2+) in aqueous solution on the electronic properties of SiO2-supported graphene. We find that, without applying any external potential, cations can shift the Fermi energy of initially hole-doped graphene by ∼200 meV up to the Dirac point, thus counteracting the initial substrate-induced hole dop…
An original 3D coordination polymer constructed from trinuclear nodes and tetracarboxylato spacers
2021
A novel 3D coordination polymer, ∞3[{Cu3(felden)}4(btec)3]·17H2O, has been assembled using cationic trigonal nodes, [CuII3(felden)]3+, generated by a tricompartmental ligand, H3felden, which results from the Schiff condensation reaction between 2,4,6-triformylphloroglucinol and N,N-dimethylethylenediamine. The tetraanion of the 1,2,4,5-benzenetetracaboxylic acid (H4btec) was employed as a spacer. The structure of 1 shows large icosahedral cavities and channels and the magnetic interaction between the copper(II) ions within the triangles is weak and antiferromagnetic.
A deep-blue emitting charged bis-cyclometallated iridium(iii) complex for light-emitting electrochemical cells
2013
We report here a new cationic bis-cyclometallated iridium(III) complex, 1, with deep-blue emission at 440 nm and its use in Light-emitting Electrochemical Cells (LECs). The design is based on the 2′,6′-difluoro-2,3′-bipyridine skeleton as the cyclometallating ligand and a bis-imidazolium carbene-type ancillary ligand. Furthermore, bulky tert-butyl substituents are used to limit the intermolecular interactions. LECs have been driven both at constant voltage (6 V) and constant current (2.5 mA cm−2). The performances are significantly improved with the latter method, resulting overall in one of the best reported greenish-blue LECs having fast response (17 s), light intensity over 100 cd m−2 an…
Formation and Rupture of Schottky Nanocontacts on ZnO Nanocolumns
2007
In this paper, the electrical transport and mechanical properties of Pt/ZnO Schottky nanocontacts have been studied simultaneously during the formation and rupture of the nanocontacts. By combining multidimensional conducting scanning force spectroscopy with appropriated data processing, the physical relevant parameters (the ideality factor, the Schottky barrier height, and the rupture voltage) are obtained. It has been found that the transport curves strongly depend on the loading force. For loading forces higher than a threshold value, the transport characteristics are similar to those of large-area Schottky contact, while below this threshold deviations from strictly thermionic emission …
Magneto-optical Investigations of Nanostructured Materials Based on Single Molecule Magnets Monitor Strong Environmental Effects
2007
The determination of the magnetic properties of molecular magnets in environments similar to those used in spintronic devices is fundamental for the development of applications. Single-molecule magnets (SMMs) are molecular cluster systems that display magnetic hysteresis of dynamical origin at low temperature. As they behave like perfectly monodisperse nanomagnets and show clear macroscopic quantum effects in their magnetic properties, they are extremely appealing candidates for the forthcoming generation of molecular devices: they have been proposed as efficient systems for quantum computation, ultra-high-density magnetic recording media, and molecular spintronic systems. These attractive …
Hydration Behaviour of Sufonated Polyetheretherketone (SPEEK) Membranes
2018
Polymer electrolyte membranes (PEM) have a potential to become power sources in automotive industry and other household applications. PEM such as sulfonated polyetheretherketone (SPEEK) have acceptable operating temperature range but proton conductivity is dependent on amount of sulfonic groups attached to the polymer backbone (degree of sulfonation). At the same time, the sulfonic groups cause sorption of water from surrounding vapour or liquid. This factor may lead to mechanical failure if membrane absorbs too much water. Modification of PEM by adding ionic liquids (IL) may provide good proton conductivity but presence of water could also be critical factor of membrane stability as in hig…