Comparative Study of the Ferroelectric Specific Heat in TGS and DTGS

Abstract

A Comparative study has been made of the specific heat in single crystals of triglycine sulfate (TGS) and deuterated triglycine sulfate (DTGS). Measurements were performed (a) in the temperature interval 100–400 K, and (b) around the respective critical regions (at small temperature intervals ∼0.02°C). In the low temperature region, both experimental curves were almost coincident, and they showed a temperature dependence indicative of strong anomalous anharmonicity. The heats of transition (ΔQ=1.90±0.10 joule/g.) and entropy change (ΔS=(6.21±0.30)×10⁻³ joule/g°C) were almost the same for both crystals. The specific heat discontinuity was substantially different in both cases, ΔC_p=0.24±0.03 joule/g°C for TGS, and ΔC_p=0.48±0.03 joule/g°C for DTGS. Calculations based on both the thermodynamic theory and the statistical theory of ferroelectrics show fair agreement with the data.