A VITREOUS DIPOLAR CRYSTAL - 146 TRICHLORO NAPHTHALENE

X-ray diffraction shows that 146 trichloro-naphthalene exists as two crystallographic forms near 290 K: an ordered phase p and a, a “cristallo-rotative” one. On freezing, the a phase gives a vitreous crystal at 77 K. During warming, differential scanning analysis shows the transformation from vitreous crystal to crystallo-rotative crystal. The transformation onset is at Tgnear 180 K, continuing up to 210 K, and is reversible. Thermostimulated currents confirm the transition with a maximum current near 210 K. By fractional polarisation, the thermally stimulated currents exhibit compensation phenomena at 289 K, a temperature very close that of the α-ft transformation seen by permittivity variations. Molecular reorientation motions are highly cooperative in the crystallo-rotative phase with activation enthalpies from 0.3 to 1.1 eV. © 1991, Taylor & Francis Group. All rights reserved.