Wyniki wyszukiwania - BazTech

1

Nowoczesne spojrzenie na konfiguracje elektronowe i układ okresowy pierwiastków, czyli o efektach relatywistycznych w chemii

Orlik Marek

Wiadomości Chemiczne

|

2023

|

[Z] 77, 9-10

833--871

EN

The article describes in an accessible, conceptual way various types of relativistic effects, which are an important part of modern chemical education, practically absent in textbooks, however allowing for a better understanding of the properties of chemical elements and their compounds. This description was preceded by a concise non-relativistic characterization of electrons in multi-electron atoms, in terms of radial probability densities, in order to explain the dependence of electron energies on the principal (n) and orbital (l) quantum numbers. The results of recent quantum chemical calculations are discussed, which show the improved energy sequence of ns and (n-1)d orbitals in transition elements and explain the electron configurations of both neutral atoms and cations of the 3d and 4d block elements. The description of the relativistic effects begins with early Dirac concept of spin-orbit coupling as causing the splitting of the degenerate p, d and f orbitals for two sets of spinors. The role of this splitting in the stability of the respective oxidation states of the cations is discussed. Another important type of relativistic effects, confirmed only in the 1970s, operates in atoms of high nuclear charge (starting from 6. period) in which electrons move at a speed close to the speed of light. The resulting relativistic increase in the mass of the moving electron causes the stabilization of s and p orbitals, and destabilization of d and f orbitals. Representative examples of the influence of all relativistic effects on the properties of elements and their compounds are given (including mercury liquidity or the color of gold). In particular, relativistic effects specific for blocks 5d, 6p, 4f, 5f, 6d, and 7p were discussed. The possibilities of predicting further expansion of the periodic table with elements up to the atomic number of about 170 are outlined, based on taking into account both the relativistic effects for electrons and the stability of superheavy atomic nuclei. The article is addressed to chemists of all branches of this discipline.

2

Ab initio study of GdCo5 magnetic and magneto-optical properties

Mahdi M., Djabri A., Koc M. M., Boukhalfa R., Erkovan M., Chumakov Yu., Chemam F.

Materials Science Poland

|

2019

|

Vol. 37, No. 2

182--189

EN

The full potential linearized augmented plane wave method (FLAPW) including the spin-orbit coupling has been used to study the structural, electronic and magnetic properties of GdCo5 compound. The calculations were performed within the local spin density approximation (LSDA) as well as Coulomb corrected LSDA + U approach. The study revealed that the LSDA + U method gave a better representation of the band structure, density of states and magnetic moments than LSDA. It was found that the spin magnetic moment of Co (2c) and Co (3g) atoms in the studied compound is smaller compared to the one in bulk Co. The optical and magneto-optical properties and the magneto-optical Kerr effect have also been investigated.

3

Electric-dipole spin resonance in wurtzite ZnO

Michaluk E., Wilamowski Z., Błoniarz J., Mycielski A.

Optica Applicata

|

2006

|

Vol. 36, nr 2-3

291-296

EN

The electron spin resonance (ESR) measurements of the electric-dipole spin resonance (EDSR) of donor-bound electrons in ZnO wurtzite crystals are reported. This phenomenon was measured in longitudinal Voigt geometry (E1 | | B0 c) at low magnetic field and at low microwave frequency. The ESR transitions observed consist of two comparable signals: magnetic dipole spin resonance (MDSR) and electric dipole spin resonance (EDSR).

4

Electrically detected spin resonance

Błoniarz J., Wilamowski Z.

Optica Applicata

|

2006

|

Vol. 36, nr 2-3

285-289

EN

An amplitude and a line shape of electrically detected signal of spin resonance are discussed. Since the signal scales with changes of spin polarization under resonance condition it is proportional to longitudinal spin relaxation. The analysis shows that such a method of detection of spin resonance is especially useful for low dimensional semiconductor structures.

5

Spintronics in semiconductors

Wilamowski Z., Werpachowska A.M.

Materials Science Poland

|

2006

|

Vol. 24, No. 3

803--808

EN

For the last years spin effects in semiconductors have been of great interest not only in the context of solid state physics, but also for their potential usage in technology. In this paper we give a short review of spintronic materials, in which electron spin as an additional degree of freedom is exploited. Afterwards, we discuss the properties of classic, non-magnetic semiconductors, where the efforts are put on enriching the traditional semiconductor technology engaging the electrical effects of spin effects. Various phenomena and scientific state of the art is highlighte

6

Spin uncoupling in methane activation

Minaev B. F.

Bulletin of the Polish Academy of Sciences. Chemistry

|

2000

|

Vol. 48, No. 2

131-143

EN

Activation of the C-H bond in methane by interaction with transition metal (TM) atom and organometallic complex can be considered by correlation diagram which involves the triplet 3(oo*) excited state localized on the activated bond in combination with the high-spin state of the TM species. This correlation diagram explains why the low-spin state of the TM species is reactive to such a catalytic process, and why the high-spin state in nonreactive. Complexes of the type MCp(CO), where Cp = CsHs, M = Co, Rh, Ir, and their ability to activate the C-H bond of methane are considered in detail. Following calculations of Siegbahn and others the isovalent complex of cobalt (M = Co) is entirely inert toward methane in contrast to the rhodium and iridium systems. At the same time all complexes are active in reaction with the CO molecule. In addition to Siegbahn's explanation of the triplet ground state nature of the cobalt complex, spin-orbit coupling analysis is given, which demonstrates the importance of spin uncoupling in the singlet state reactivity. A similar concept can be applied for methane activation processes by bare TM atoms.