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Correlation Mechanism to Change Lattice Parameters and Phase Transitions in Compounds with Intermediate Valency
Author(s) -
Manakova L. A.,
Ionov S. P.
Publication year - 1989
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221550208
Subject(s) - valency , coulomb , condensed matter physics , lattice (music) , electron , impurity , phonon , chemistry , phase transition , anderson impurity model , physics , quantum mechanics , linguistics , acoustics , philosophy , organic chemistry
For compounds with intermediate valency (IV) a microscopic mechanism of changing the parameters of crystal lattice depending on the impurity concentration (or pressure) and temperature is suggested. The mechanism is based on the exact account of the Coulomb correlation and hybridization between f‐ and d‐electrons. For that the “non‐Fröhlich” terms in the electron—phonon interaction proportional to the first and second derivatives of the Coulomb interactions and overlapping integrals of f‐ and d‐electrons are considered. These terms in the electron—phonon interaction contain an explicit dependence on the interatomic distance and cause additional (as compared to the termal) shifts of the lattice sites on account of the Coulomb correlations. The corresponding additions for the lattice parameter depend on the concentration of the impurities x (or pressure) and temperature T . The dependences of the lattice parameter on x and T are obtained for both, the semiconductor and metallic phase. The equation for the transition temperature into the state with IV and the existence condition of this state with concentration are obtained. A comparison of the dependences with experimental ones obtained on the basis of the correlation mechanism is made on the example of the solid solutions Sm 1− x R x 3+ S (R 3+ is a rare earth element for instance Gd, Y etc.).