Dielectric Study of the Phase Transition in K _{1− x} Li _x TaO ₃

Abstract

Comprehensive dielectric measurements have been performed on the mixed-crystal system K1−xLixTaO3 in order to check the hypotheses done about the ferroelectric and the dipole glass behaviours and identify their respective origins. These have been made for a series of concentrations (1.5% < x < 5%), spanning the critical concentration xc ≅ 2%, and over the frequency range from 20 Hz to 2 MHz. The broad frequency and temperature ranges have allowed us to cover, in the same study, both Li-related dielectric relaxations as well as the transition for x > xc and to investigate their relationship. We have gathered new strong supports (quasi-discontinuity in the dielectric constant, thermal hysteresis) of first-order character of the transition for x = 3.5% and 5% and studied the kinetics within this hysteresis for x = 5%. We have also identified the high-temperature relaxation with an activation energy of about 2700 K, which we attribute to Li pairs undergoing π flips at high temperatures. It is argued that, at low temperatures, these pairs are sources of static random fields responsible for the disorder of the low-temperature phase.

Lithium-induced dielectric relaxations in potassium tantalate ceramics

“…10 An activation energy inside that range is obtained in the current work for KLT with x = 0.02, revealing that relaxation B in this composition stems from the flipping of Li + K pairs. Regarding the fitting of the Vogel-Fulcher relation to the high-T experimental data in KLT ceramics with x = 0.05 and 0.10, the relaxation parameters obtained evidence the apparent off-centre displacements of small lithium ions on the large potassium sites within polar clusters.…”

“…These two peaks have been associated with two distinct relaxational processes, termed low-T and high-T relaxations. [9][10][11] The low-T process with an activation energy of 78<U<125 meV has been associated with isolated Li ions hopping from one <001> position to another. 12 However, the high-T process with an activation energy of 181<U<241 meV is poorly understood.…”

“…On the basis of acoustic measurements, it was suggested that this latter process could be due to 180°reorientations of Li ions within dipole pairs. 10 While K 1-x Li x TaO 3 single crystals have been intensively studied with considerable success in the last decades, to the best of our knowledge no systematic experimental work has yet been carried out in KLT-based ceramics, so far. This is because polycrystalline KTaO 3 is hard to process as a phase pure stoichiometric compound with relatively high density.…”

Thermal conductivity of K1−xLixTaO3 and KTa1−xNbxO3

“…On cooling, the interactions between the dipoles are believed to result in polar nanoregions [1,2], although the nature of polar nanoregions is probably different from those found in relaxors with strong random fields [17]. For 0 ox o2.2%, the crystal remains in the cubic phase down to T-0 K, and the classic relaxor-like behavior is observed in dielectric susceptibility below 100 K [18,19]. A ferroelectric transition is found at low-temperature for x4 2.2%, but the frequency dependence in dielectric susceptibility persists at least up to x E5% [18,20].…”

Non Ergodic Aging in an Orientational Glass

“…Typical data of the real and imaginary parts of the dielectric constant [3] at several frequencies and of the real and imaginary parts of the elastic constant [4] also at various frequencies are shown as a function of temperature for two KLT samples, one with x = 0.015 (figure 1) and the other with x = 0.05 (figure 2).…”