1. Akimov, B.A., Dmitriev, A.V., Khokhlov, D.R., and Ryabova, L.I., Carrier Transport and Non-Equilibrium Phenomena in Doped PbTe and Related Materials,Phys. Status Solidi B, 1993, vol. 137, pp. 9–55.
2. Khomskii, D.I., Electronic Phase Transitions and the Problem of Mixed Valence,Kvantovaya teoriya tverdykh tel (Quantum Theory of Solids), Lifshits, I.M., Ed., Moscow: Mir, 1982, pp. 70–129.
3. Ramakrishnan, T.V., Theory of the Mixed Valent State,J. Magn. Magn. Mater., 1987, vol. 63/64, pp. 529–534.
4. Adroja, D.T. and Malik, S.K., Valence Fluctuation and Heavy Fermion Behavior in Rare Earth and Actinide Based Compounds,J. Magn. Magn. Mater., 1991, vol. 100, pp. 126–138.
5. Wachter, P., Intermediate Valence and Heavy Fermions, inHandbook on the Physics and Chemistry of Rare Earths, vol. 19:Lanthanides/Actinides: Physics-II, Amsterdam: Elsevier, 1994, pp. 177–382.