Properties Of Mixed Valence Compounds Research Articles

New approach to the anomalies of thermodynamic properties of mixed valence compounds

A new interpretation of a specific heat and thermal expansion anomalies is proposed for mixed valence compounds and applied to Sm1−xLaxB6 and Ce1−xLaxNi. These thermodynamic quantities are considered as a superposition of contributions resulting from lattice and electron (f- and conduction electron) excitation spectra.

Theory of the electronic properties of mixed valent compounds

A self-consistent Green function theory of the Anderson lattice Hamiltonian is presented. The approximations include spin and charge fluctuations beyond mean field and are similar to previous approximations made for the impurity problem by Theumann (1969). The self-energy integral equations are solved exactly and the static physical properties are obtained for almost the entire strongly mixed valent regime. The temperature dependence of the electronic specific heat, C(T), gamma (T)=C(T)/T, densities of states, Fermi level and valence are discussed for both one and two electrons per atom. The behaviour of gamma (T) is similar to that found experimentally.

Spectroscopic properties of mixed valence compounds in the impurity model

Abstract Spectroscopic properties of mixed valence compounds are studied using the Anderson impurity model. Recent theoretical developments using the large spin and orbital degeneracy N f of the f-level are discussed. It is shown how exact results for various spectroscopies can be obtained in the limit N f →∞. The behaviour of the f-level spectral density is discussed in detail for T = 0. The occurrence of the ‘Kondo peak’ is shown to reconcile the large values of the coupling Δ between the f-level and the conduction states as obtained by comparison with spectroscopic measurements with former estimates from thermodynamic data. Values for Δ and the f-occupancies, n f , are given for various Ce compounds.

Mixed valencies: Symmetries and phonon phenomena

The consequences of electron-hole symmetry, the structure of phase diagrams and lattice properties of mixed valence compounds are discussed on the basis of the periodic Anderson model which was extended to include the interaction of 4f electrons and lattice vibrations.

Self-consistent alloy treatment of the periodic anderson model: Susceptibility and specific heat of intermediate valence compounds

To describe the electronic properties of mixed valence compounds we study the periodic Anderson model within the frame of the alloy analog approximation. In this approach the model Hamiltonian is replaced by the sum of two single-particle alloy Hamiltonians the parameters of which have to be determined self-consistently. The alloy problem is solved within the coherent potential approximation. In contrast to other treatments of the periodic Anderson model this approximation scheme is exact in both trivially solvable limits of vanishing hybridization and Coulomb repulsion, respectively. For model parameters corresponding to a mixed valence situation only nonmagnetic solutions of the self-consistency equations exist. After discussing the limit of small hybridization analytically we numerically calculate the magnetic susceptibility and the electronic specific heat as a function of temperature for realistic values of the hybridization and Coulomb repulsion. The results are in very good qualitative agreement with experimental data.