The nature of iron-oxygen vacancy defect centers in PbTiO3

TL;DR

This study investigates the microscopic structure of iron-oxygen vacancy defect centers in ferroelectric PbTiO3 using both experimental and computational methods, revealing substitutional behavior and local charge compensation mechanisms.

Contribution

It provides a detailed analysis combining superposition modeling and density functional theory to elucidate the structure of defect centers in PbTiO3.

Findings

Fe3+ substitutes Ti4+ as an acceptor center

The defect associate is oriented along the c-axis

PbTiO3 remains tetragonal down to 12 K

Abstract

The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of 1.0721.