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Fluctuating Defects in the Incipient Relaxor K1-xLixTaO3 (x=0.02)



C. Stock, Peter M. Gehring, G. Xu, Daniel Lamago, Dmitry Reznik, M. Russina, Jinsheng Wen, Lynn A. Boatner


We report neutron scattering measurements of the structural correlations associated with the apparent relaxor transition in K1-xLixTaO2 for x=0.02 (KLT(0.02)). This compound displays a broad and frequency-dependent peak in the dielectric permittivity, which is the accepted hallmark of all relaxors. However, no evidence of elastic diffuse scattering, nor any soft mode anomaly, has been observed in KLT(0.02) [J. Wen et al., Phys. Rev. B 78, 144202 (2008)], a situation that differs sharply from that in other relaxors such as PbMg1/3Nb2/3O3. We resolve this dichotomy by showing that the structural correlations associated with the transition in KLT(0.02) are purely dynamic at all temperatures, having a timescale on the order of THz. These fluctuations are also overdamped, non-propagating, and spatially uncorrelated. By studying their temperature dependence and comparing to identical measurements made on pure KTaO3, we are able to identify these fluctuations with local ferroelectric regions associated with the Li+ doping and the peak in the dielectric response. The ferroelectric transition that is induced by the introduction of Li^u+6 is therefore characterized by quasistatic fluctuations, which is a marked contrast to the soft harmonic-mode-driven transition observed in conventional perovskite ferroelectrics like PbTiO3. The dynamic, glass-like, structural correlations in KLT(0.02) are much faster than those measured in random-field-based lead-based relaxors, which exhibit a frequency scale of order of GHz and are comparatively better correlated spatially. Our results support the view that random fields give rise to the relaxor phenomena, and that the glass-like dynamics observed here characterize a nascent response.
Physical Review B


Ferroelectrics, Relaxors, Neutron Scattering, Relaxational Modes, Quasielastic Scattering, Perovskites


Stock, C. , Gehring, P. , Xu, G. , Lamago, D. , Reznik, D. , Russina, M. , Wen, J. and Boatner, L. (2014), Fluctuating Defects in the Incipient Relaxor K<sub>1-x</sub>Li<sub>x</sub>TaO<sub>3</sub> (x=0.02), Physical Review B, [online], (Accessed April 16, 2024)
Created December 23, 2014, Updated October 12, 2021