Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Study of the 4f and valence band density of states in rare-earth metals. II. Experiment and results

Abstract: For pt.I see ibid., vol.11, p.113 (1980). The 4f and valence states of all metallic rare earths have been studied using X-ray photoelectron spectroscopy (XPS) for the occupied part and bremsstrahlung isochromat spectroscopy (BIS) for the unoccupied part. It is found that the bandwidth increases from Gd to Lu, and that the valence band spectra are in fair agreement with APW calculations. The intensities of the 4f final-state multiplets are well described in terms of the coefficients of fractional parentage. There is a symmetry between the fn XPS and f14-n BIS spectra. The observed energies of the 4f excitations correspond to transitions to completely screened final states. These values enable one to predict the elements which are liable to interconfiguration fluctuation when their 4f levels are shifted to EF by the chemical environment or by compression. The large Coulomb correlation energies, U, which prevent the formation of 4f bands in these elements, are directly obtained from the authors' spectra, and are found to be in good agreement with recent calculations. The linewidths and singularity indices of the XPS and BIS 4f lines are determined and discussed.

Ruthenium-based layered cuprates RuSr2LnCu2O8 and RuSr2(Ln1+xCe1−x)Cu2O10 (LnSm, Eu and Gd)

Abstract: We synthesized layered cuprates where the intermediate layer between the CuO 2 blocks consists of vertex sharing RuO 6 octahedra. The (idealized) stoichiometries of these compounds are RuSr 2 LnCu 2 O 8 (Ru-1212) and RuSr 2 (Ln 1+ x Ce 1− x ) Cu 2 O 10 (Ru-1222), where Ln is one of the three neighboring lanthanides Sm, Eu and Gd. The analogy to the isostructural Nb based compounds, as well as simple valence counting, suggest that Ru is pentavalent in these compounds. Both 1212 and 1222 compounds are semiconducting when prepared in air and rapidly cooled to room temperature. Metallic behavior and superconductivity can be achieved for various compositions upon appropriate annealing.

Electron Transfer Mechanisms upon Lithium Deintercalation from LiCoO2 to CoO2 Investigated by XPS

Abstract: Lithium deintercalation of LixCoO2 from x = 1 to x ≈ 0 has been carried out electrochemically. The changes in the electronic structure from LiCoO2 to CoO2 have been investigated by X-ray photoelectron spectroscopy (XPS) to bring some new developments about the electron transfer mechanisms upon lithium deintercalation. All available XPS core peaks (Co 2p, Co 3p, Co 3s, O 1s, F 1s, P 2p, C 1s) and valence spectra have been analyzed. The contributions of the electrode material and of the electrode/electrolyte interface have been clearly distinguished. We show that cobalt and oxygen simultaneously undergo a partial oxidation process and that the sole participation of oxygen atoms to the charge transfer process, as it is sometimes assumed, can be excluded. The surface film consists of organic and inorganic species resulting from degradation of the electrolyte.

Large spin splitting in the conduction band of transition metal dichalcogenide monolayers

Abstract: We study the conduction band spin splitting that arises in transition metal dichalcogenide (TMD) semiconductor monolayers such as MoS${}_{2}$, MoSe${}_{2}$, WS${}_{2}$, and WSe${}_{2}$ due to the combination of spin-orbit coupling and lack of inversion symmetry. Two types of calculation are done. First, density functional theory (DFT) calculations based on plane waves that yield large splittings, between 3 and 30 meV. Second, we derive a tight-binding model that permits to address the atomic origin of the splitting. The basis set of the model is provided by the maximally localized Wannier orbitals, obtained from the DFT calculation, and formed by 11 atomiclike orbitals corresponding to $d$ and $p$ orbitals of the transition metal (W, Mo) and chalcogenide (S, Se) atoms respectively. In the resulting Hamiltonian, we can independently change the atomic spin-orbit coupling constant of the two atomic species at the unit cell, which permits to analyze their contribution to the spin splitting at the high symmetry points. We find that---in contrast to the valence band---both atoms give comparable contributions to the conduction band splittings. Given that these materials are most often $n$-doped, our findings are important for developments in TMD spintronics.

VALENCE: a program for calculating bond valences

Abstract: The DOS program VALENCE is designed to calculate bond valences from bond lengths and vice versa. It can also calculate bond-valence sums and average bond lengths, and can determine bond-valence parameters from the bonding environments of different cations.