On electron transport in ZrB$_{12}$, ZrB$_{2}$ and MgB$_{2}$ in normal state

We report on measurements of the temperature dependence of resistivity, $\rho(T)$, for single crystal samples of ZrB$_{12}$, ZrB$_{2}$ and polycrystalline samples of MgB$_{2}$. It is shown that cluster compound ZrB$_{12}$ behaves like a simple metal in the normal state, with a typical Bloch – Grüneisen $\rho(T)$ dependence. However, the resistive Debye temperature, $T_{R}=300$ K, is three times smaller than $T_{D}$ obtained from specific heat data. We observe the $T^{2}$ term in $\rho(T)$ of all these borides, which could be interpreted as an indication of strong electron-electron interaction.