DIELECTRIC AND DILATOMETRIC STUDIES OF PHASE-TRANSITIONS IN (ND4)3D(SEO4)2 AND ISOTOPE EFFECT

Dielectric and dilatometric measurements were made for the deuterated crystal (ND4)3D(SeO4)2. For comparison the dilatometric measurement was also made for the undeuterated crystal (NH4)3(SeO4)2. Two phase transitions were found at +55°C and at about +29°C for (NH4)3H(SeO4)2 besides the two phase transitions previously reported. Deuteration rises the Curie temperature by about 34°C, showing important role of the O—H—O bonds playing in the ferroelectric transition. The Curie-Weiss constant and spontaneous polarization of the deuterated crystal are 3.7x103K and 2.4 μC.cm-2 at —170°C, respectively. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.