Complex dielectric behaviours in $BiFeO_{3}/Bi_{2}Fe_{4}O_{9}$ ceramics

TL;DR

This study investigates the complex dielectric properties of a ceramic mixture of BiFeO3 and Bi2Fe4O9, revealing temperature-dependent relaxation behaviors and a ferroelectric phase transition influenced by grain boundary strains.

Contribution

It provides new insights into the dielectric relaxation mechanisms and phase transition origins in mixed ceramic materials with grain boundary effects.

Findings

Dielectric response shows temperature-activated relaxation features.

A ferroelectric phase transition is observed and decays with repeated heating.

Phase transition is linked to strain at grain boundaries due to lattice mismatch.

Abstract

The complex dielectric permittivity of a sintered ceramic tablet consisting of 70.5 % $BiFeO_{3}$ and 27.7% $Bi_{2}Fe_{4}O_{9}$ was analyzed as a function of temperature from -120 {\deg}C to 230 {\deg}C. The results reveal a complicated dielectric response with temperature activated relaxation features. They also reveal a ferroelectric phase transition that decayed with repeated heating cycles of the tablet. The source of the behaviour is assigned to relaxation processes happening along the grain boundaries of differing compositions in the tablet. The origin of the phase transition is traced to locally induced strains on grain boundaries because of unit cell size mismatch between $BiFeO_{3}$ and $Bi_{2}Fe_{4}O_{9}$.