Dielectric properties of NaF-B2O3 glasses doped with certain transition metal ions

Dielectric constant epsilon, loss tan delta a.c. conductivity sigma and dielectric breakdown strength of NaF-B2O3 glasses doped with certain transition metal ions (viz. Cu2+, VO2+, Ti4+ and Mn4+) are studied in the frequency range 10(2)-10(7) Hz and in the temperature range 30-250 degrees C. The values of epsilon, tan delta sigma(a.c.) are found to be the highest for Cu2+ doped glasses and the lowest for Mn4+ doped glasses. Activation energy for a.c. conduction and the value of dielectric breakdown strength are found to be the lowest for Cu2+ doped glasses and the highest for Mn4+ doped glasses. With the help of infrared spectra, increase in the values of epsilon and tan delta of these glasses with frequency and temperature are identified with space charge polarization. An attempt has been made to explain a.c. conduction phenomenon on the basis of quantum mechanical tunneling model (QMT)/carrier barrier hopping model.