Electronic transport in MgB2,AlB2 and ZrB2 -: a comparative study

We report on the temperature dependence of the resistivity (p) and the absolute thermopower (S) of the polycrystalline title materials and of AlB2 single crystals. For all samples rho(T) exhibits a Bloch-Grilneisen-like temperature dependence, with large characteristic temperatures 0(R) (approximate to0(D)-the Debye temperature). At high temperatures the thermopower S(T) for ZrB2 (n-type) is almost the mirror image of S(T) for MgB2 (p-type) while S(AlB2) is very small for all temperatures. The density of states distribution N(E) around E-F seems to play a dominant role in determining S(T) of these materials. ln(T) terms in the low-temperature rho(T) and S(T) of ZrB2 samples bear evidence for weak localization in 2D. (C) 2002 Elsevier Science B.V. All rights reserved.