Giant Negative Thermal Expansion in the Iron Perovskite SrCu₃Fe₄O₁₂

Big and cold: Strong internal compression of the Sr ion in the novel perovskite SrCu3Fe4O12 (see structure) leads to giant negative thermal expansion (NTE) between 170 and 270 K. Mössbauer spectroscopy shows charge disproportionation of FeIV to FeIII and FeV below 200 K. Thus, the isoelectric substitution of the A-site cation can induce a drastic change of the structural and electronic properties in ACu3Fe4O12 perovskites.