Dielectric characteristics of melt grown doped KMgF3 crystals

Results obtained from dielectric studies carried out on melt grown KMgF3 crystals doped with 5% NiF2 are reported. The variation of the dielectric constant (epsilon' and epsilon), the dielectric loss (tan 3), and the conductivity (sigma(ac)) at different temperatures (298-1073 K) and frequencies (0.5 kHz-10 MHz) of the applied alternating current field is analyzed. It is observed that epsilon' remains constant up to a particular temperature (approximate to800 K) and then rises sharply, attains a maximum value of 1575 at 1060 K and 0.5 kHz and then decreases abruptly. The variation of epsilon' with frequencies of the applied field at different temperatures is described with respect to the lower frequency range of 0.5-100 kHz and higher frequency range of 100 kHz-10 MHz. The dependence of tan delta, epsilon and sigma(ac) on temperature and frequency of the applied field (0.5 kHz-10 MHz) is described and discussed. The empirical equations obtained fit very well with the experimental data. These equations are suggestive of functional relationship between the dielectric parameters epsilon', tan delta and sigma(ac) and the temperature and frequency of the applied field. The activation energy is calculated and its value is found to be 1.55, 0.75 and 0.42 eV at 1, 5, and 10 MHz frequencies, respectively. The non-linearities and anomalous behavior of epsilon' near the transition temperature suggests the possibility of melt grown doped KMgF3 crystals to be a ferroelectric material. (C) 2003 Elsevier B.V. All rights reserved.