Automated spectrometer for dielectric measurements over the frequency range 107-10-4 Hz and from 350 to 77 K

A new dielectric spectrometer is described which covers the frequency range from 10 MHz to 0.1 mHz, and the temperature interval 350-77 K. This spectrometer can be used in both isothermal (IT) or isofrequency (IF) modes. In IT mode, the sample temperature is stabilized and the dielectric parameters are obtained as functions of frequency. In IF mode, one or several frequencies can be automatically selected and the measurements are carried out the temperature varying linearly with time. In practice, the cooling rates are chosen between 10 and 0.1 K/min. The IF mode is quite suitable for investigations of all temperature-dependent dielectric parameters and allows accurate and sensitive studies of phase transitions in low-conductivity materials. The spectrometer is controlled by a microcomputer. All data are stored then treated to be fitted according to different theoretical models. The versatility of this spectrometer was illustrated by recent investigations of supercooled isotropic polar liquids specially near the glass transition temperature and nematic-smectic transitions in liquid crystals