Weak Ferroelectricity on Organic Crystal Trichloroacetamide

概要

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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 εb′ along the b-axis shows a discontinuous change at TC=354.9 K and a hump at T0=356.8 K upon heating. A thermal hysteresis of about 1.5 K can be seen only for the transition at TC. The Curie–Weiss relation holds above 358 K; the paraelectric Curie temperature and the Curie–Weiss constant are estimated as Tp=350.8 K and C=7.6 K, respectively. The pyroelectric charge Ppyr along the b-axis obeys the relation of Ppyr-P0=α(TC-T)β in a narrow temperature range of 0≤TC-T≤10 K; the critical index β 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 TC is due to a structural phase transition. Hydrostatic pressure effects on the TC were measured by means of a standard DTA method; the transition temperature increases with pressure as a slope of dTC/dp=0.30 K/MPa. The result indicates that the ferroelectric phase transition at TC is an order-disorder type.
2001-10-15