Ferroelectric specific heat of telluric acid ammonium phosphate single crystal near T c

Abstract

Precise specific heat data on good quality Telluric Acid Ammonium Phosphate (TAAP) have been obtained in the vicinity of the ferroelectric-paraelectric phase transition ( T c ≈ 44.8 °C). The experimental specific heat discontinuity at T c, ΔC P exp( T c) = 0.085J/gK, is somewhat lower than the expected value, Δ C P cal( T c) = 3/2 Nk B(1 − 3 g) −1 ϱ −1 = 0.129J/gK, with g = 0.28 determined from spontaneous polarization Ps( T). Using a linear background interpolation for the non-ferroelectric contributions to the specific heat, we get Δ S exp( T c) = 5.25 × 10 −3J/gK<Nk Bϱ −1 Ln2 = 9.65 × 10 −3J/gK (transition entropy), and Δ Q exp( T c) = 1.608J/g<1/2 Nk B T cϱ −1 = 2.214J/g (transition heat).