Valency

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

Physical Properties and Behavior of Allotropically Pure α-, β- and γ-Ce

Abstract: Cerium was the first material found to undergo a valency change. X-ray studies in 1949–1950 revealed that when Ce was compressed to modest pressures (> 8 kbar at 300 K)1 or cooled to low temperature ( 12%) while the crystal structure remained the same. When these authors discussed this unusual behavior with their colleagues, both Zachariasen3 and Pauling4 independently suggested that this volume contraction corresponded to a valence change of 3 for γ-Ce to 4 for α-Ce, i.e. the 4f electron of γ-Ce was promoted to the valence band, leaving the 4f level of α-Ce empty. Several other authors subsequently reanalyzed the physical properties of the phases involved in the valence change and they concluded that about 0.5 to 0.67 of an electron per atom is transferred from the 4f level to the valence band.5 Today the consensus of scientists favors the 0.67 value. Furthermore, Gschneidner and Smoluchowski point out that the valences of the two phases involved (γ- and α-Ce) change with temperature and pressure. As a result of this valence change, the γ-α pressure-temperature phase boundary ends at a critical point. Ce is the only solid known to have a critical point.

Effects of the Counter Ion Valency on the Colloidal Interaction between Two Cylindrical Particles

Abstract: In this study, the effects of counter ion valency of the electrolyte on the colloidal repulsion between two parallel cylindrical particles were investigated. Electrostatic interactions of the cylindrical particles were calculated with the variation of counter ion valency. To calculate the electrical repulsive energy working between these two cylindrical particles, Derjaguin approximation was applied. The electrostatic potential profiles were obtained numerically by solving nonlinear Poission-Boltzmann (P-B) equation and calculating middle point potential and repulsive energy working between interacting surfaces. The electrical potential and repulsive energy were influenced by counter ion valency, Debye length, and surface potential. The potential profile and middle point potential decayed with the counter ion valency due to the promoted shielding of electrical charge. On the while, the repulsive energy increased with the counter ion valency at a short separation distance. These behaviors of electrostatic interaction agreed with previous results on planar or spherical surfaces.

Effect of RE ion valency variation in Tb and Dy doped magnetic SrFe 10−x RE x O 19 hexaferrite

Abstract: M-type hexaferrites are focused of much research because of its outstanding properties such as high saturation magnetism (Ms), high coercivity (Hc), high permeability and low conductive looses, excellent chemical stability, and corrosion resistivity. Because of these properties M-type ferrite find wide industrial applications ranging from microwave devices to recording media [1]. The magnetic and electric properties of these ferrites can be tuned by replacing Fe3+ or Sr2+/Ba2+ with magnetic or non-magnetic ion. The result of these substitutions is to alter magnetocrystalline anisotropy and magnetization to suite particular application. Recent reports have shown the effect of high concentration of RE3+ doping in the M-type of ferrite [2, 3, 4, 5]. The work by Wang [5], the magnetism reduced from 64 emu/g to 64 emu/g with doping of lanthanum (La) with x=0.25at 1200°C while the coercivity was increased greatly from 1.95 kOe to 3.4 kOe. Karimi's group [6] showed that the small amount of Ce doping in ferrite leads to variation in the lattice parameter due to dual valence Ce3+/4+. In the present study we have synthesized SrRE x Fe 12-x O 19 (RE=Tb or Dy) where RE ions are known display multivalence. Consequently it is important to understand the concomitant structural and magnetic changes resulting from variation in RE valency. The valency changes in turn changes their ionic radii and anisotropy.