Specific Heat Peculiarities in (NH₄)₂SbF₅

Precise measurements of the specific heat in (NH₄)₂SbF₅ crystal have been performed using an ac-calorimeter. Anomalies previously connected with phase transitions at 293 K, 169 K, and 139 K are detected and discussed. Two second order transitions at 293 K and 169 K are confirmed. Thermal parameters (as the excess enthalpy Δ H, and the excess entropy ΔS) are estimated and possible mechanisms are presented. The anomaly at 139 K is attributed to an overcritical trace of isostructural phase transition. Simplified model calculations of the excess of specific heat are compared with the Δ c_p measured experimentally.

Keywords:

• Ferroelectrics
• specific heat
• phase transitions

PACS numbers:

• 64.70 kb
• 65.40 Ba
• 77.80Bh

Acknowledgments

This work was supported by the University of Wrocław (grant 2016/W/IFD/2004).

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005