FeAs: Heat capacity, enthalpy increments, other thermodynamic properties from 5 to 1350 K, and magnetic transition

Abstract:

The heat capacity of iron monoarsenide has been determined by adiabatic calorimetry from 5 to 1030 K and bv drou calorimetrv relative to 298.15 K over the range 875 to 1350 K. A small h-type transition is observed at ?;, = (70.95 kO.02) K. It is related & the disappearance of a doubly helically ordered magnetic-spin structure on heating. The obviously cooperative entropy increment of transition is only A&JR = 0.021. The higher-temperature heat capacity rises considerably above lattice expectations. Part of the rise is ascribed to low-spin electron redistribution in iron, while the further excess above 800 K presumably arises from a beginning low- to high-spin transition, possibly connected with interstitial defect formation in the MnPtype structure. FeAs melts at about 1325 K with A,,,Hk=6180R.K. Thermodynamic functions have been evaluated and the values of C,,,(T), S:(T), H:(T), and @i(T), are 6.057R, 7.513R, 1177R.K, and 3.567R at 298.15 K, and 8.75R, 16.03R, 6287R.K, and 9.74512 at 1000 K.

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