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Dielectric properties and lattice dynamics of Ca-doped K$_{0.95}$Li$_{0.05}$TaO$_{3}$

S. Wakimoto·G. A. Samara·R. K. Grubbs·E. L. Venturini·L. A. Boatner·G. Xu·G. Shirane·S. -H. Lee
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Abstract

Relaxor behavior and lattice dynamics have been studied for a single crystal of K$_{1-x}$Li$_x$TaO$_3$ $(x=0.05)$, where a small amount of a Ca impurity ($\sim 15$~ppm) was incorporated. The dielectric measurements revealed Debye-like relaxations with Arrhenius activation energies of 80 and 240 meV that are assigned to Li$^+$ dipoles and the Li$^+$-Li$^+$ dipolar pairs, respectively. In the neutron scattering results, diffuse scattering ridges appear around the nuclear Bragg peaks below $\sim 150$ K and phonon line broadening features start to appear at even higher temperatures suggesting that polar nano-regions (PNR's) start to form at these temperatures. These results are supported by the dielectric data that reveal relaxor behavior starting at $\sim 200$ K on cooling. From analyses of the diffuse intensities, the displacements include a uniform phase shift of all of the atoms in addition to the atomic displacements corresponding to a polarization vector of the transverse optic soft ferroelectric mode, a finding that is analogous to that in the prototypical relaxor material Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$.

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S. Wakimoto, G. A. Samara, R. K. Grubbs, E. L. Venturini, L. A. Boatner, G. Xu, G. Shirane, S. -H. Lee. 2006-08-03. Dielectric properties and lattice dynamics of Ca-doped K$_{0.95}$Li$_{0.05}$TaO$_{3}$. https://doi.org/10.1103/physrevb.74.054101

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