Resistivity and thermal conductivity measurements were made of bulk samples prepared by using a standard method or a 1-step technique. The latter samples, due to their high density and purity, exhibited residual resistivity values as low as 0.5μΩcm and thermal conductivity values as high as 215W/mK. These were higher than single-crystal values. The thermal and electrical data of all the samples were analyzed within the framework of the Bloch–Gruneisen equation, giving reliable parameter values. In particular, the temperature resistivity coefficient, obtained both from resistivity and thermal conductivity, was 10 times larger in dirty samples than in clean samples. This result supports the hypothesis that π and σ bands conduct in parallel, with prevailing π conduction in clean samples and σ conduction in dirty samples.

Two-Band Effects in the Transport Properties of MgB2. M.Putti, V.Braccini, E.Galleani, F.Napoli, I.Pallecchi, A.S.Siri, P.Manfrinetti, A.Palenzona: Superconductor Science and Technology, 2003, 16, 188-92