The exploration of superconducting iron-free pnictides with a ThCr2
-type or related structure and the study of their superconducting properties are important in order to get a deeper understanding of the pairing mechanism of 122 iron pnictides. Here we review the properties of 122-type iron-free pnictides superconductors with structures similar to that of BaFe2
. Evidence of fully gapped nature of superconducting state has come from the specific heat and thermal conductivity measurements for BaNi2
, and nuclear magnetic and quadrupole resonance measurements for CaPd2
etc. Combined with the fact that no magnetism is observed in 122-type iron-free pnictides superconductors, the majority of evidence suggests that most of these compounds are conventional electron–phonon-mediated superconductors.
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