Успехи физики металлов (Sep 2005)
Covalent-Band Model of the Condensed Matter
Abstract
The Coulomb interaction of electron pair in ri of neighbour ions at Rj within the tight-binding representation comes either to the covalent-bond energy (Γ) or to the hopping integral (t) that is calculated for two-dimensional systems such as fullerenes (FUL) and carbon nanotubes (CNT). The theory of semiconductor (s/c) systems leads to the dependence of bond energy Γ(T) on temperature T, which is caused by the chemical (covalent) bond fluctuations (CBF). The calculated s/c characteristics (forbidden-band width Eg(T), effective mass of electrons m∗e and holes (|m∗h|>m∗e), electrical resistance (ER), etc.) depend on the set of parameters – Γ and CBF. The catalytic properties of FUL and CNT, the hydrogen accumulation into them, the work function are expressed through Γ(T). The calculation precision is conditioned by the definiteness of introduction of the many-electron operator spinors (MEOS) in the Fock spaces. Fe atomic and magnetic diagrams are caused by the competition of band and covalent (within the MEOS representation) 3d−t2g- and eg-electrons. Antibonding electrons of neighbour sites in γ-Fe form antiferromagnetic (AFM) order. Its Neel temperature TN102 K) that is explained by the |Γe| increase on a particle surface. At T<TM, the t2g-electrons’ localization in the covalent state with Sr spin at the r site leads to the ferromagnetic (FM) order of α-Fe when T<Tc∼Atex(T). The dependence TM(B) on magnetic field B (even in the presence of FM phase) is strengthened by the competition of band and covalent energies of t2g-electrons. The observed nonlinearities for magnetization M2(T) and susceptibility χ−1(T) are interpreted as the effect of Atex(T) renormalization by CBF spectrum. The theory of ferroelectric (FE) phase of dielectrics within the deformation FE model interprets the square-law dependence of FE polarization P(T) and its jump Р(Тс)∼Р(0) in the first-kind transition points Tc for BaTiO3 and other FE crystals.
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