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 40-125K are ascribed to the individual hopping by 90 degrees and 180 degrees of dipoles created by the off-centre Li ions. Another relaxation observed at 100-200K is related to 180 degrees-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 135-235K for x = 0.10 and attributed to 90 degrees-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.






Tkach, A; Almeida, A; Moreira, JA; Espinha, A; Chaves, MR; de la Cruz, JP; Vilarinho, PM

nossos autores


This work was supported by Portuguese Foundation for Science and Technology (FCT) through the Project PTDC/CTM/64805/2006. A Tkach also thanks FCT for financial support (SFRH/BPD/34607/2007).

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