Lithium-induced dielectric relaxations in potassium tantalate ceramics

This work reports the effect of lithium doping on the dielectric and polar properties of potassium tantalate. Experimental data were obtained in K 1− x Li x TaO 3 ceramics with x = 0, 0.02, 0.05 and 0.10 by measuring both the dielectric permittivity from 10 2 to 10 8 Hz, and polarization under an ac electric field driven at 2.5 Hz, for temperatures from 10 to 300 K. The dielectric permittivity exhibits all the relaxations reported for K 1− x Li x TaO 3 single crystals. Two dielectric relaxations observed at 40–125 K are ascribed to the individual hopping by 90° and 180° of dipoles created by the off-centre Li ions. Another relaxation observed at 100–200 K is related to 180°-flips of Li pairs for x = 0.02 and of polar clusters of interacting Li ions for x = 0.05 and 0.10. In addition to that, an additional relaxation not reported before is presented at 135–235 K for x = 0.10 and attributed to 90°-reorientation of Li polar clusters. Both the change from an Arrhenius to a Vogel–Fulcher dependence with increasing lithium content, and the emergence of slim P ( E ) hysteresis loops around the relaxation temperatures show that the relaxation dynamics in K 1− x Li x TaO 3 can be understood if a crossover from a dipolar glass to a relaxor-like behaviour is assumed.