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

Published

December 24, 2014

Author(s)

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

Abstract

We report neutron scattering measurements of the structural correlations associated with the apparent relaxor transition in K_1-xLi_xTaO₂ 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 PbMg_1/3Nb_2/3O₃. 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.

Citation

Physical Review B

Volume

90

Issue

22

Pub Type

Journals

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Keywords

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

Citation

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_1-xLi_xTaO₃ (x=0.02), Physical Review B, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916592 (Accessed April 24, 2024)