Study of the Second-Order Ferroelectric Transition in Tri-Glycine Sulfate

Results of measurements of the dielectric constant, dielectric nonlinearity and spontaneous polarization of tri-glycine sulfate are given. These data demonstrate clearly that this material exhibits a second-order ferroelectric transition. The properties discussed are described in terms of the usual expansion of the free energy in even powers of the polarization F(P,T)=F(O,T)+A(T-T
0
)P
²
+BP
⁴
+CP
⁶
, where A,T
0
,B and C are constants and T and P are the temperature and polarization, respectively. From the various data taken it is found that A=1.96×10
⁻³
(°C)
⁻¹
, T
0
=49.8°C,B=2.0×10
⁻¹⁰
(esu/cm
²
)
^-2
and C=8.4×10
⁻¹⁹
(esu/cm
²
)
⁻⁴
. From these results the nonlinearity of the dielectric constant above the Curie point is calculated at various temperatures.