Lithium-induced dielectric relaxations in potassium tantalate ceramics

Abstract

To cite this version:A Tkach, A Almeida, J Agostinho Moreira, A Espinha, M R Chaves, et al.. Lithium-induced dielectric relaxations in potassium tantalate ceramics. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (31) 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 a.c. electric field driven at 2.5 Hz, for temperatures from 10 to 300 K. The dielectric permittivity exhibits all the relaxations reported for K1-xLixTaO3 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. Besides 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 K1-xLixTaO3 can be understood if a crossover from a dipolar glass to a relaxor-like behavior is assumed.Keywords: Quantum paraelectricity, Lithium doped potassium tantalate, Dielectric relaxtion properties, Microscopic mechanisms AbstractThis work reports the effect of lithium doping on the dielectric and polar properties of potassium 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 relaxorlike behavior is assumed.

Dielectric Relaxation, Local Structure and Lattice Dynamics in Mn-Doped Potassium Tantalate Ceramics

“…As reported previously, undoped KT ceramics upon cooling display a continuous increase of the dielectric permittivity to ε ′ ≈ 4000 without frequency dispersion [ 10 , 11 ]. In contrast, for the Mn-doped KT ceramics, the maximum attainable value of ε ′ is only ≈1400 (see Figure 1 a), and the ε ′( T ) dependence reveals a diffuse peak with a frequency-dependent amplitude and position, suggesting a dielectric relaxation.…”

“…The resulting powders were dried and calcined at 875 °C for 8 h. The calcined powders were milled again for 5 h to reduce the particle size below 5 μm, and uniaxially pressed (100 MPa) into pellets, 10 mm in diameter. The pellets, covered with powder of the same composition to mitigate the loss of potassium, were sintered in closed alumina crucibles in air at 1350 °C for 1 h with a heating and cooling rate of 5 °C/min, similarly to the conditions used previously for preparing undoped and Li-doped KT ceramics [ 11 ]. After sintering, the pellets exhibited a density of ≈88% and an average grain size of ≈1.8 μm.…”

“…Among KT-based compounds, K 1− x Li x TaO 3 solid solutions have been studied intensively, wherein displacements of small Li + ions on K sites generate strong local dipole moments that couple electrostatically to the KT’s polar soft mode [ 8 , 9 ]. As a result, both dielectric relaxations and a ferroelectric phase transition were reported for the K 1− x Li x TaO 3 system [ 8 , 9 , 11 , 12 , 13 ]. Similar to Li-doped KT and Mn-doped ST, Mn-doped (0.01% to 0.3%) KT single crystals [ 14 , 15 , 16 ] exhibit a dielectric relaxation which has also been attributed to a positional disorder of Mn 2+ on K sites [ 15 ].…”

Coexistence of the relaxor-like and ferroelectric behavior in K1-xLixTaO3

“…The hysteresis of the phase transition has the value of DT C D 3 K. The maximum of the linear electric susceptibility attains x 0 1 D 5800 at 65 K. Figure 2 to the reorientation by 90 (p/2 flipping) and by 180 (p flipping) of Li C between equivalent sites at orthogonal axes. [11,23] The relaxation mechanism observed between 80 and 150 K is due to reorientation by 180 (p pair flipping) of coupled dipoles of clusters of Li C pairs along the same axis. [11,23] The broad peaks of x 0 1 depend on frequency and vary from x 0 1 D 8820 at 59 K to x 0 1 D 2300 at 83 K for the frequencies 20 Hz and 536 kHz of the ac probing field, respectively.…”

“…[11,23] The relaxation mechanism observed between 80 and 150 K is due to reorientation by 180 (p pair flipping) of coupled dipoles of clusters of Li C pairs along the same axis. [11,23] The broad peaks of x 0 1 depend on frequency and vary from x 0 1 D 8820 at 59 K to x 0 1 D 2300 at 83 K for the frequencies 20 Hz and 536 kHz of the ac probing field, respectively. The arrow shows a jump in the value of the linear x 0 1 , and an imaginary x 00 1 part of the electric susceptibility for all frequencies at T C ð # Þ D 51 K (Figure 2).…”