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Abstract. Temperature dependent comparative EXAFS studies of Ba 1Àx K x BiO 3 superconducting oxides and copper based superconductors with hole (La 2Àx Sr x CuO 4 ) and electron (Nd 2Àx Ce x CuO 4Àd ) doping showed the common dynamical local structure nonuniformity observed as the double-well potential of oxygen ion oscillations. Obtained data evidence that these local structure nonuniformity arises from the local dynamic charge ordering due to different electronic structure of the neighbouring BiO 6 or CuO n (n ¼ 4; 6) complexes in perovskite-like lattice. Based on the experimental results, the phenomenological description was proposed which allowed us to establish the correlations between the local and the macroscopic properties and to explain the insulator-metal phase transition and the appearance of the superconductive state with both hole and electron doping of parent BaBiO 3 , La 2 CuO 4 and Nd 2 CuO 4 insulators. The presented results makes clear the role of electron-phonon coupling in the mechanism of high temperature superconductivity.

Samarium sulfide (SmS) belongs to the class of compounds with homogeneous intermediate valence, which is observed in a metal phase at a pressure of տ 0.6 GPa above the point of the dielectric-metal phase transition because of a partial delocalization of the 4 f 6 electron [1]. Upon the transition, the crystal lattice decreased significantly in volume with the retention of the NaCl symmetry. An intermediate-valence state can also be achieved by replacing a portion of samarium ions by other smaller radius rare earth or transition metal ions (Y 3+ , Yb 3+ , Gd 3+ , etc.). It is believed that the resulting chemical contraction serves as an equivalent of external pressure. However, attempts to initiate the dielectric-metal phase transition using chemical contraction upon the insertion of bivalent ions, such as Ca 2+ , were unsuccessful, although x-ray absorption spectroscopic data indicated the appearance of an intermediate-valence state [2]. This suggests that doping and the resulting chemical contraction inevitably affect the electronic and crystal structures at a local level and thereby change the properties of the intermediatevalence state and the macroscopic properties of the compound.The recently growing interest in compounds based on samarium sulfide is considerably related to a number of anomalies observed in these compounds, such as a negative coefficient of thermal expansion in the metallic phase of SmS Thus, in order to reveal the nature of the intermediate-valence state, determine the role of doping, and explain the macroscopic properties of Sm 1 -x Y x S, a study of the local electronic and crystal structure peculiarities is brought to the forefront. For this purpose, in this work, we used a combination of x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) techniques, which allowed us to simultaneously study the valence states and local environment parameters of the test ions.The samples with the yttrium contents x = 0.17 and 0.33 were prepared at the Ioffe Physicotechnical Institute, Russian Academy of Sciences (St. Petersburg, Russia), and the samples with x = 0.25 and 0.45 were prepared at Tohoku University (Sendai, Japan).The x-ray absorption spectra of Sm 1 -x Y x S ( x = 0.17, 0.25, 0.33, and 0.45) were measured over the temperature range 20-300 K above the Sm L III and Y K edges at the beamlines E 4 and A 1 of the HASYLAB synchrotron center (DESY, Germany). The use of a Si (111