Off-centered Pb interstitials in PbTe

TL;DR

This study uses first-principles calculations to reveal that off-centered Pb interstitials in PbTe are more stable and prevalent than previously thought, influencing its lattice properties and potential dipole formations.

Contribution

It demonstrates that Pb interstitials in PbTe prefer off-centered positions along [111], significantly increasing defect density predictions and explaining anharmonic lattice behavior.

Findings

Off-centered Pb interstitials are more stable than on-centered ones.

Defect density is ~5.6 times higher at 900 K due to multi-stable structures.

Off-centered defects induce long-range lattice relaxation and potential dipoles.

Abstract

In this work, we calculate the defect properties of low-symmetry Pb interstitials in PbTe using first-principles density-functional theory calculations. We break the symmetry imposed on on-centered interstitial defects and show that the lowest ground state of Pb interstitial defects is off-centered along the [111] directions. Due to the four multi-stable structures with low defect formation energies, the defect density of Pb interstitials is expected to be ~5.6 times larger than previous predictions when PbTe is synthesized at 900 K. In contrast to the on-centered Pbinterstitial, the off-centered Pb interstitials in PbTe can exhibit long-range lattice relaxation toward [111] direction beyond distance of 1 nm, indicating the potential formation of weak local dipoles. This result provides an alternative explanation for the emphanitic anharmonicity of PbTe.