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

TL;DR

This study investigates the dielectric and lattice dynamics of Ca-doped K$_{0.95}$Li$_{0.05}$TaO$_{3}$, revealing relaxor behavior, formation of polar nano-regions, and atomic displacements similar to known relaxors, using dielectric and neutron scattering techniques.

Contribution

It provides new insights into the relaxor behavior and lattice dynamics of Ca-doped KLT, highlighting the formation of polar nano-regions and atomic displacement patterns.

Findings

Debye-like relaxations with specific activation energies.

Diffuse scattering and phonon broadening indicate polar nano-region formation.

Atomic displacements include a uniform phase shift similar to Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$.

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$_3$.