Specific heat of Ca0.33Na0.67Fe2As2

The specific heat of single crystal hole-doped Ca0.33Na0.67Fe2As2, T-c(onset) = 33.7 K, was measured from 0.4 to 40 K. The discontinuity in the specific heat at T-c, Delta C, divided by T-c is 105 +/- 5 mJ/mol K-2, consistent with values found previously for hole-doped Ba0.6K0.4Fe2As2 and somewhat above the general trend for Delta C/T-c vs T-c for the iron based superconductors established by Bud'ko, Ni and Canfield. The usefulness of measured values of Delta C/T-c, as an important metric for the quality of samples is discussed. (C) 2014 Elsevier Ltd. All rights reserved.