Weak ferroelectricity on organic crystal trichloroacetamide

Temperature dependence of the dielectric constant and the pyroelectric charge Were measured on the single crystal of an organic ferroelectric material, trichloroacetamide CCl3CONH2,). The dielectric constant epsilon (1)(b) along the b-axis shows a discontinuous change at T-C = 354.9 K and a hump at T-0 = 356.8 K upon heating. A thermal hysteresis of about 1.5 K can be seen only fur the transition at T-C. The Curie-Weiss relation holds above 358 K; the paraelectric Curie temperature, and the Curie-Weiss constant are estimated as T-p = 350.8 K and C = 7.6 K, respectively. The pyroelectric charge P-pyr along the b-axis obeys the relation of P-pyr - P-0 = alpha (T-C - T)(beta) in a narrow temperature range of 0 less than or equal to T-C - T less than or equal to 10 K; the critical index beta is estimated as 0.50. X-ray oscillation photographs of the b-bar samples were taken at RT and temperatures above Tc: an evidence was obtained that the weak ferroelectric anomaly at T-C is due to a structural phase transition. Hydrostatic pressure effects on the T-C were measured by means of a standard DTA method; the transition temperature increases with pressure as a slope of dT(C)/dp = 0.30 K/MPa. The result indicates that the ferroelectric phase transition at T-C is an order-disorder type.