Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

Conductance of symmetrical, unsymmetrical and mixed electrolytes. Part 3.—Examination of new model and analysis of data for symmetrical electrolytes

Abstract: In the first two papers of this series a conductance equation, based on a new model for ions in solution, was derived. The equation described charge transport in solutions containing any number of ionic species of any valency type.In this paper the model upon which the new equation is based is discussed in greater detail and the equation is used to analyse conductance data for a number of symmetrical electrolyte solutions. Excellent agreement is found between experimental results and theoretical predictions and the distance parameter values obtained show clearly the existence of solvent-separated ion-pairs (SSIP's) in many systems.

Effects of exchangeable cations on hydraulic conductivity of a marine clay

Abstract: A laboratory study of the hydraulic conductivity (HC) of a marine clay with monovalent, divalent and trivalent cations revealed large differences in HC. The exchangeable cations employed in this study are Na, K, NH4, Mg, Ca and Al in order of increasing valency. An interpretation of the results derived from consolidation tests suggests that HC is significantly affected by the valency and size of the adsorbed cations. An increase in the valency of the adsorbed cations leads to quicker rates of consolidation and higher HC, while, for a constant valency an increase in the hydrated radius of the adsorbed cations results in a lower rate of consolidation and HC. The reduction in HC was related to the dispersion and deflocculation of clay. Lower valency and higher hydrated radii of the exchangeable cations enable the double layer repulsive forces to predominate, thereby increase dispersion and defloccalation.

Charge compensation and mixed valency in LaAlO 3 /SrTiO 3 heterointerfaces studied by the FLAPW method

Abstract: The electronic structures and properties of heterointerfaces in the perovskite oxide superlattices ${\mathrm{LaAlO}}_{3}∕{\mathrm{SrTiO}}_{3}\phantom{\rule{0.3em}{0ex}}[001]$ are presented using the first-principles all-electron full-potential linearized augmented plane-wave (FLAPW) method. Superlattices with three types of interfaces, (i) electron-doped, (ii) hole-doped, and (iii) both electron- and hole-doped, are studied and compared. For the electron-doped interface, the mixed valency of Ti along with the Jahn-Teller effect are found to explain the metallicity, in agreement with experiment, whereas for the hole-doped interface metallicity is found, in contrast to experiment. Oxygen vacancies introduce an additional $n$-type carrier to compensate the holes present at the interface, which now becomes insulating and agrees well with experiment. For a system with both types of interfaces, the metallicity found for the unrelaxed structure is changed to insulating after relaxation is included. For all cases, the relaxation results in a complicated buckled geometry, which is a good indication of the adjustment due to polarity discontinuity. Our findings support recent experimental results, namely, (i) the mixed-valence character of Ti at the electron-doped interface, and (ii) the existence and importance of oxygen vacancies at the hole-doped interface.

Three-dimensional valency mapping in ceria nanocrystals.

Abstract: Using electron tomography combined with electron energy loss spectroscopy (EELS), we are able to map the valency of the Ce ions in CeO2–x nanocrystals in three dimensions. Our results show a clear facet-dependent reduction shell at the surface of ceria nanoparticles; {111} surface facets show a low surface reduction, whereas at {001} surface facets, the cerium ions are more likely to be reduced over a larger surface shell. Our generic tomographic technique allows a full 3D data cube to be reconstructed, containing an EELS spectrum in each voxel. This possibility enables a three-dimensional investigation of a plethora of material-specific physical properties such as valency, chemical composition, oxygen coordination, or bond lengths, triggering the synthesis of nanomaterials with improved properties.