Dielectric Relaxation and Phase Transition at Cryogenic Temperatures in 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 Ceramics

TL;DR

This study investigates dielectric, structural, and magnetic properties of a lead-based relaxor ferroelectric ceramic, revealing phase transitions and low-temperature anomalies linked to domain dynamics and structural changes.

Contribution

It provides new insights into low-temperature phase behavior and dielectric relaxation mechanisms in 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 ceramics, including the identification of a monoclinic phase transition.

Findings

Relaxor ferroelectric transition around 350K with Vogel-Fulcher freezing.

Appearance of a non-ergodic relaxor phase at room temperature.

Low-temperature dielectric anomaly at 160K linked to domain freezing.

Abstract

Dielectric measurements on 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 ceramic in the temperature range 90K to 470K shows a relaxor ferroelectric transition around 350K with a Vogel-Fulcher freezing temperature of 338K and appearance of a non-ergodic relaxor ferroelectric phase of tetragonal structure at room temperature. This non-ergodic phase reenters into the relaxor state at low temperatures as evidenced by the appearance of a frequency dependent anomaly in the imaginary part of the dielectric constant around 160K, similar to those reported in other relaxor ferroelectric based morphotropic phase boundary ceramics. The polarization relaxation time for the 160K anomaly also follows Vogel-Fulcher type temperature dependence. Temperature dependent magnetization measurements show that this low temperature anomaly is not linked with any magnetic transition. Elastic modulus and low temperature x-ray diffraction (XRD) measurements reveal a tetragonal to monoclinic phase transition around 225K. It is argued that the low temperature dielectric dispersion around 160K results from the freezing of mesoscopic conformally miniaturized monoclinic domains formed inside the parent tetragonal domains below the structural phase transition temperature of 225K.