Study on dielectric dispersion of neodymium phosphate ceramics

The dielectric properties of neodymium phosphate ceramics prepared by the molten urea method are measured in the frequency region 102 to 107 Hz and in the temperature range -193 to 315 0C. Dielectric constant (ε) at room temperature (∼ 30 0C) decreases with frequency upto 105 Hz beyond which it reaches a constant value: dielectric loss (tan δ) behaves in a similar way. The values of ε and tan δ at 30 0C and 106 Hz for this material are 7 and 6 x 10-4, respectively. ε as a function of temperature contains two stages of increase: (1) a slow stage upto -35 0C and (2) a fast one beyond -35 0C which is considerably frequency dependent, ε having higher values at lower frequencies: similar behavior is exhibited by tan δ. Conductivity, σ, versus 1/T graphs for NdPO4 give the activation energy for conduction in the intrinsic region as 0.6 eV. log Δε against 1/T plots (where Δε is the difference between the dielectric constant at any temperature and the value at -193 0C) yields an activation energy value of 0.66 eV in the same temperature region. This suggests that the same charge carriers are responsible for the two processes (increases in ε and conductivity) in the high temperature region. (author)