On the link between Octahedral Rotations and Conductivity in the Domain Walls of BiFeO3

TL;DR

This study investigates the potential link between octahedral straightening and enhanced conductivity in BiFeO3 domain walls, finding that structural changes may not directly cause increased conductivity.

Contribution

The paper provides computational analysis of lattice and octahedral rotations in BiFeO3 walls, challenging the assumed correlation between octahedral straightening and conductivity.

Findings

Lattice parameter expands by ~1% perpendicular to the wall.

Octahedral rotation angle straightens by about 4 degrees.

Straightening of octahedra does not necessarily correlate with bandgap reduction.

Abstract

We analyze the hypothetical link between octahedral straightening and increased conductivity inside the domain walls of BiFeO3. Our calculations for 109 degree walls predict a lattice parameter expansion of c.a. 1 percent in the direction perpendicular to the wall, and an associated straightening of the octahedral rotation angle of 4 degrees, which is comparable to that observed in the high temperature metallic phase of BiFeO3. On the other hand, in the closely related family of rare-earth orthoferrites, straighter octahedra do not correlate with increased bandgap, which suggests that the correlation between octahedral straightening and bandgap reduction in BiFeO3 is perhaps fortuitous and not necessarily the cause of increased conductivity at the walls.