Properties
CaB6 has been investigated in the past due to a variety of peculiar physical properties, such as superconductivity, valence fluctuation and Kondo effects. However, the most remarkable property of CaB6 is its ferromagnetism. It occurs at unexpectedly high temperature (600 K) and with low magnetic moment (below 0.07 per atom). The origin of this high temperature ferromagnetism is the ferromagnetic phase of a dilute electron gas, linkage to the presumed excitonic state in calcium boride, or external impurities on the surface of the sample. The impurities might include iron and nickel, probably coming from impurities in the boron used to prepare the sample.
CaB6 is insoluble in H2O, MeOH (methanol), and EtOH (ethanol) and dissolves slowly in acids. Its microhardness is 27 GPa, Knoop hardness is 2600 kg/mm2), Young modulus is 379 GPa, and electrical resistivity is greater than 2·1010 Ω·m for pure crystals. CaB6 is a semiconductor with an energy gap estimated as 1.0 eV. The low, semi-metallic conductivity of many CaB6 samples can be explained by unintentional doping due to impurities and possible non-stoichiometry.
Read more about this topic: Calcium Hexaboride
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