Dielectric properties of solid are very sensitive to the local electric field distribution and change even with a slight variation of physical and chemical changes. The dielctric spectrum can be studied by applying low ac voltage in certain frequency and temperature ranges for different substances by heating them in a furnace at different temperatures with +/- 1C change.The following trends are noticed:

[I] Ɛ decreases with the increase in frequency but increases with the increase in temperature up to Curies temperature(where ferroelectric substance changes to non ferroelectric) possessing the highest value at Curies temperature and at certain lowest frequency. But it decreases further. For example for BaTiO3 NP with Curies temperature 50C (which is shifted to some what lower value) , Ɛ has the highest value of 5679 at 50C at 100HZ while its lowest Ɛ (23.8) was recorded at 130 C and 4MHz.

[II] The dissipation factor[D]( loss of energy due to electrical conduction, dielectric relaxation, dielectric resonance and hystersis; relaxation being most important) increases with increase in temperature up to Curies temperature but continues to increase even when the frequency is incresed to high value(10kHz for BaTiO3) where the relaxation peak appears for all the temperatures.

[III]The relaxation peaks move towards the higher frequency with the increasing temperature up to Curies temperature(50C for BaTiO3) beyond which , the relaxation peaks move towards the lower frequency but D values decrease with increasing frequency beyond relaxation frequency.Again, D values show a decrease at higher frequencies but there is a small change at elevated temperature. In case of BaTiO3, it varies in between 048-0.60 at 100Hz and 0.31-0.65 at One MHz over a wide range of temperature.

[IV] AC concuctivity[α ac] also changes as:

α ac=Ɛ^ .Ɛ0 . ω .D.

where

ω= 2π. f.