An Anomalous Phase in the Relaxor Ferroelectric Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$

TL;DR

This study reveals an unusual phase in PZN relaxor ferroelectric, showing a distinct outer layer with a phase transition and an inner cubic lattice with ferroelectric polarization, challenging typical relaxor behavior.

Contribution

It uncovers a novel anomalous phase in PZN with a dual structure, highlighting a complex interplay between surface and bulk properties during phase transition.

Findings

Outer layer undergoes a structural phase transition at 410 K.

Inner lattice remains cubic with minimal parameter variation.

Bragg peak broadening indicates a structural change at T_C.

Abstract

X-ray diffraction studies on a Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN) single crystal sample show the presence of two different structures. An outer-layer exists in the outer most $\sim$ 10 to 50~$\mu$m of the crystal, and undergoes a structural phase transition at the Curie temperature $T_C\approx410$ K. The inside phase is however, very different. The lattice inside the crystal maintains a cubic unit cell, while ferroelectric polarization develops below $T_C$. The lattice parameter of the cubic unit cell remains virtually a constant, i.e., much less variations compared to that of a typical relaxor ferroelectric, in a wide temperature range of 15 K to 750 K. On the other hand, broadening of Bragg peaks and change of Bragg profile line-shapes in both longitudinal and transverse directions at $T_C$ clearly indicate a structural phase transition occurring.