Heat capacity, third-law entropy, and low-temperature physical behavior of bulk hematite (α-Fe2O3)

The constant pressure heat capacity of a bulk hematite powder was measured using a Quantum Design physical properties measurement system (PPMS). The results of two series showed good precision and agreed well with measurements reported by Westrum and Grønvold. The standard molar entropy at T = 298.15 K was calculated to be (87.32 ± 2) J · mol−1 · K−1 for Series 1 and (87.27 ± 2) J · mol−1 · K−1 for Series 2, which are in good agreement with the value of (87.40 ± 0.2) J · mol−1 · K−1 (originally 20.889 cal · deg−1 · mole−1) calculated by Westrum and Grønvold. No anomaly was observed for the Morin transition, and theoretical fits below T = 15 K required a ferromagnetic T3/2 term.