Dielectric properties and lattice dynamics of Ca-doped K${}_{0.95}$Li${}_{0.05}$TaO${}_3$

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${}_{1\mathrm{/}3}$Nb${}_{2\mathrm{/}3}$)O${}_3$.