DIELECTRIC-RELAXATION STUDIES ON CAO-MGO-AL2O3-SIO2 GLASS-CERAMICS DOPED WITH TIO2

CaO-MgO-Al2O3-SiO2 glasses of composition 24.4, 17.5, 5.6 and 52.5 all by wt% respectively, were prepared with 2% by weight of TiO2 as dopan t. The samples were then crystallised at 800, 900 and 1000 degrees C. The dielectric constant epsilon, loss tan delta and hence ac conductiv ity sigma were measured in the frequency range 5 x 10(5)-10(7) Hz and in the temperature range 30-350 degrees C. The highest rate of increas e of epsilon with temperature at a fixed frequency is observed for the samples crystallised at 1000 degrees C; this has been attributed to t he space charge polarisation due to the point defects formed in the sa mples during crystallisation. The variation of dielectric loss with te mperature for crystalline samples has exhibited dielectric relaxation effects. The relaxation phenomenon has been analysed by a pseudo Cole- Cole plot method; presence of several types of dipoles in these cerami cs was established and these were attributed to the association of pai rs of cation vacancies with divalent positive ions such as Ca2+, Mg2+.