The temperature dependence of permittivity in MgO and Fe-MgO single crystals

The permittivities ( epsilon ') of undoped MgO and Fe-doped Fe--MgO single crystals have been measured over the temperature range 20-650 deg C for frequencies between 500 Hz and 50 kHz. From 25- approx 200 deg C the temperature dependence of epsilon ' fits well with Havinga's formula. Above 200 deg C the permittivity changes much more rapidly than the Havinga formula predicts, the variation being greater in Fe-doped specimens. The frequency dependence of epsilon ' is also temperature-dependent; > 200 deg C the value of epsilon ' falls more rapidly with frequency than would be expected. The effect is more pronounced for MgO with 12 900 p.p.m. Fe. The results are discussed in terms of a contribution to the measured permittivity arising from temperature-enhanced conductivity. 25 ref.--AA