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The magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and thermal conductivity measurements in a wide temperature range have been performed on UCoGa 5 single crystals. On the basis of the susceptibility maximum at 650 K and the phonon part of the thermal conductivity, a mixed-valence state of uranium in this compound has been postulated. On the other hand, a normal positive behavior of magnetoresistivity rules out the possibility of spin fluctuation as a mechanism driving the susceptibility through the maximum. In turn, the thermopower results may support both kinds of many-body behaviors. The electronic structure has also been studied by combining x-ray photoemission spectroscopy results with those obtained in the band structure calculations. In the latter the tight-binding linear muffin-tin orbital method in the atomic sphere approximation has been applied. A very good agreement between the experimental and calculated data has been achieved. A complex satellite structure of the core level spectra supports an idea of the presence of the valence instability in this compound. This idea is also concluded from the comparison of obtained experimental data with some similar rare earth and uranium ternary compounds.

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