Polar and non-polar atomic motions in the relaxor ferroelectric PLZT from dielectric, anelastic and NMR relaxation

TL;DR

This study investigates the atomic motions in the relaxor ferroelectric PLZT using dielectric, anelastic, and NMR relaxation measurements, revealing distinct polar and rotational dynamics and their temperature-dependent behaviors.

Contribution

It provides new insights into the coexistence of polar and rotational atomic motions in PLZT, highlighting their temperature dependence and coupling.

Findings

Dielectric susceptibility shows a frequency-dependent maximum at ~250 K.

NMR relaxation indicates broad rotational modes of O octahedra at lower temperatures.

Rotational instabilities occur in both Zr-rich and Ti-rich regions of the phase diagram.

Abstract

Dielectric, anelastic and ^139La NMR relaxation measurements have been made on the relaxor ferroelectric Pb(1-3x/2)La(x)Zr(0.2)Ti(0.8)O(3) (PLZT) with x = 0.22. The dielectric susceptibility exihibits the frequency dispersive maximum due to the freezing of the polar degrees of freedom around T ~250 K. The anelastic and especially NMR relaxation, besides this maximum, indicate an intense and broad component at lower temperatures, attributed to rotational modes of the O octahedra, weakly coupled to the polar modes. It is discussed why such short range rotational instabilities, known to occur in the Zr-rich rhombohedral region of the PLZT phase diagram, might appear also in the Ti-rich region.