On electron transport in ZrB12, ZrB2, and MgB2 in normal state

We report on measurements of the temperature dependence of resistivity, ρ(T), for single-crystal samples of ZrB12, ZrB2, and polycrystalline samples of MgB2. It is shown that the cluster compound ZrB12 behaves as a simple metal in the normal state, with a typical Bloch-Gruneisen ρ(T) dependence. However, the resistive Debye temperature, TR=300 K, is three times smaller than TD obtained from specific heat data. We observe the T2 term in ρ(T) of all these borides, which could be interpreted as an indication of strong electron-electron interaction.