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.

High Power Factor and Enhanced Thermoelectric Performance of SnTe-AgInTe2: Synergistic Effect of Resonance Level and Valence Band Convergence

Abstract: Understanding the basis of electronic transport and developing ideas to improve thermoelectric power factor are essential for production of efficient thermoelectric materials. Here, we report a significantly large thermoelectric power factor of ∼31.4 μW/cm·K2 at 856 K in Ag and In co-doped SnTe (i.e., SnAgxInxTe1+2x). This is the highest power factor so far reported for SnTe-based material, which arises from the synergistic effects of Ag and In on the electronic structure and the improved electrical transport properties of SnTe. In and Ag play different but complementary roles in modifying the valence band structure of SnTe. In-doping introduces resonance levels inside the valence bands, leading to a significant improvement in the Seebeck coefficient at room temperature. On the other hand, Ag-doping reduces the energy separation between light- and heavy-hole valence bands by widening the principal band gap, which also results in an improved Seebeck coefficient. Additionally, Ag-doping in SnTe enhances the...

Metallophilic interactions in closed-shell copper(I) compounds--a theoretical study.

Abstract: Cuprophilic interactions in neutral perpendicular model dimers of the type (CH 3 CuX) 2 (X = OH 2 , NH 3 , SH 2 , PH 3 , N 2 , CO, CS, CNH, CNLi) were analyzed by ab initio quantum-chemical methods. The basis set superposition error for the weakly interacting CH 3 CuX subunits is significant and is discussed in detail. A new correlation-consistent pseudopotential valence basis set for Cu, derived at the second-order Moller - Plesset level suppresses considerably the basis set superposition error in Cu-Cu interactions compared to the standard Hartree-Fock optimized valence basis set. This allowed the first accurate predictions of cuprophilicity, which has been the subject of considerable debate in the past. The dependence of the strength of cuprophilic interactions on the nature of the ligand X was addressed. The Cu-Cu interaction increases with increasing o-donor and π-acceptor capability of the ligand and is approximately one-third of the well-documented aurophilic interactions. By fitting our potential-energy data to the Hershbach-Laurie equation, we determined a relation between the Cu-Cu bond length and the Cu-Cu force constant; this is important for future studies on vibrational behaviour. The role of relativistic effects on the structure and the interaction energy is also discussed. Finally we investigated cuprophilic interactions in (CH 3 Cu) 4 as a model species for compounds isolated and characterized by X-ray diffraction.

Ferromagnetism in magnetically doped III-V semiconductors.

Abstract: The origin of ferromagnetism in semimagnetic III-V materials is discussed. The indirect exchange interaction caused by virtual electron excitations from magnetic impurity acceptor levels to the valence band can explain ferromagnetism in GaAs(Mn) in both degenerate and nondegenerate samples. Formation of ferromagnetic clusters and the percolation picture of phase transition describes well all available experimental data and allows us to predict the Mn-composition dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.