Calorimetric Study on Phase Transitions in (NH₄)₃H(SO₄)₂

Abstract

Specific heat of (NH₄)₃H(SO₄)₂ was measured in a temperature range 90 K\lesssimT\lesssim440 K covering the four phase transitions. The transition entropies were estimated to be ΔS_I–II=2.5±0.2, ΔS_II–III=2.10±0.08, ΔS_III–IV=0.51±0.03 and ΔS_IV–V=0.53±0.03 in the units of cal·mol⁻¹·deg⁻¹ for the I–II, II–III, III–IV and IV–V phase transitions, respectively.