Dielectric and thermal behaviour of holmium tartrate trihydrate crystals

Measurements on dielectric constant of holmium tartrate trihydrate crystals at frequencies of the applied a.c. in the range 1 kHz to 1 MHz and at temperature in the range 30 degrees C to 330 degrees C are reported. The dielectric constant epsilon' increases with temperature at all frequencies, attains a peak near 250 degrees C, and then decreases as the temperature goes beyond 250 degrees C. The anomalous dielectric behaviour at near about 250 degrees C is attributed to be as a result of crystal lographic/polymorphic phase transition brought about in the material. The results on the dielectric behaviour of the material are supplemented by results of thermal analysis viz., TG and DTA. Thermogravimetric and differential thermal analytic techniques have been used to study thermal behaviour of the material. It is shown that the material is thermally stable up to 220 degrees C beyond which it decomposes through three stages till the formation of holmium oxide at 1200 degrees C. The non-isothermal kinetic parameters e.g., activation energy and the frequency factor have been evaluated for first two stages of thermal decomposition by using the integral method of Coats and Redfern.