Surface phase transitions in BiFeO3 below room temperature

TL;DR

This study investigates two low-temperature phase transitions in multiferroic BiFeO3 using diverse experimental techniques, revealing a surface phase transition at 140.3K and glassy behavior onset at 201K.

Contribution

The paper provides the first detailed experimental analysis of surface and bulk phase transitions in BiFeO3 below room temperature.

Findings

Surface phase transition at 140.3K with lattice and charge density changes

Onset of glassy behavior at 201K

Differences observed between single crystals and nanotubes

Abstract

We combine a wide variety of experimental techniques to analyze two heretofore mysterious phase transitions in multiferroic bismuth ferrite at low temperature. Raman spectroscopy, resonant ultrasound spectroscopy, EPR, X-ray lattice constant measurements, conductivity and dielectric response, specific heat and pyroelectric data have been collected for two different types of samples: single crystals and, in order to maximize surface/volume ratio to enhance surface phase transition effects, BiFeO3 nanotubes were also studied. The transition at T=140.3K is shown to be a surface phase transition, with an associated sharp change in lattice parameter and charge density at the surface. Meanwhile, the 201K anomaly appears to signal the onset of glassy behaviour.