Mechanism for the metal-conducting behavior of a CaB4 single crystal

The temperature-dependent resistivity of a pure CaB4 single crystal has been observed to demonstrate metal-conducting behavior. The normal Hall-coefficient measurement is indicative of the electrons as the conducting carriers with a room-temperature density of 4.7×1021 cm−3. The observed metal-conducting behavior can be understood using a simple model, in which the Ca ions are treated as independent Einstein harmonic oscillators embedded in a Debye rigid boron network. The ab initio calculations of band structure and density of states corroborate the experimentally observed metal-conducting behavior of CaB4, showing that it originates mainly from the p orbital of B atom and the hybridized d orbital of Ca atom.