Reentrant polar phase induced by the ferro-ionic coupling in Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles

TL;DR

This study combines theoretical modeling and experimental data to analyze how ferro-ionic coupling and size effects influence the phase behavior and polar properties of Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles, revealing reentrant polar phases.

Contribution

It introduces a comprehensive theoretical framework for predicting phase diagrams of Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles considering size and ionic effects, validated by experimental data.

Findings

Ferro-ionic coupling affects phase stability in nanoparticles.

Reentrant ferroelectric and antiferroelectric phases are observed.

Theoretical predictions align qualitatively with experimental results.

Abstract

Using the model of four sublattices, the Landau-Ginzburg-Devonshire-Kittel phenomenological approach and the Stephenson-Highland ionic adsorption model for the description of coupled polar and antipolar long-range orders in ferroics, we calculated analytically the phase diagrams and polar properties of Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles covered by surface ions in dependence on their size, surface ions density, samarium content "x" and temperature. The size effects and ferro-ionic coupling govern the appearance and stability conditions of the long-range ordered ferroelectric, reentrant ferrielectric and antiferroelectric phases in the Bi1-xSmxFeO3 nanoparticles. Calculated phase diagrams are in a qualitative agreement with the X-ray diffraction phase analysis, electron paramagnetic resonance, infra-red spectroscopy and electrophysical measurements of the Bi$_{1-x}$Sm$_x$FeO$_3$ nanopowders sintered by the solution combustion method. The combined theoretical-experimental approach allows to establish the influence of the ferro-ionic coupling and size effects in Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles on their polar properties.