Ab initioenergetics of lanthanum substitution in ferroelectric bismuth titanate

Abstract

Using first principles calculations and atomistic thermodynamics the bulk and defect properties of orthorhombic bismuth titanate (Bi₄Ti₃O₁₂) and bismuth lanthanum titanate (Bi₃.₂₅La₀.₇₅Ti₃O₁₂) have been investigated. Heats of formation, valid chemical conditions for synthesis, lanthanum substitution energies and oxygen and bismuth vacancy formation energies have been computed. The study improves our understanding of how native point defects and substitutional impurities influence the ferroelectric properties of these layered perovskite materials. It is found that lanthanum incorporation could occur on either of the two distinct bismuth sites in the structure and that the effect of substitution is to increase the formation energy of nearby native oxygen vacancies. The results provide direct atomistic evidence over a range of chemical conditions supporting the suggestion that lanthanum incorporation reduces the oxygen vacancy concentration. Oxygen vacancies contribute to ferroelectric fatigue by interacting strongly with domain walls, and therefore a decrease in their concentration is beneficial. The conditions that favor the greatest reduction in oxygen vacancy concentration are described.

Multiferroic and dielectric properties of Bi4LaTi3FeO15 ceramics

“…For our BLTF ceramics, on the one hand, similar with La-doped Bi 4 Ti 3 O 12 , the improved ferroelectricity probably comes from the structural distortion induced by La substitution [32]. On the other hand, compared with BTF, the introduction of La can suppress the evaporation of bismuth and thus decrease chemical defects, such as bismuth vacancies and the accompanied oxygen vacancies, as a result, improved remnant polarization is obtained for BLTF ceramics because of the suppressed domain pinning effect [33,34].…”

Determination of the electronic, dielectric, and optical properties of sillenite Bi12TiO20 and perovskite-like Bi4Ti3O12 materials from hybrid first-principle calculations

“…The experimental lattice parameters shown in Table I are consistent with the calculated values and the literature. [59][60][61] The Bi 4 Ti 3 O 12 structure is composed of fluorite bismuth-oxide…”

Point defect formation in M2AlC (M = Zr,Cr) MAX phases and their tendency to disorder and amorphize

“…ref. 26, and requires knowledge of the chemical potentials of the constituent elements and the application of equilibrium conditions which prevent the formation of competing phases. The method has recently been applied to Ti-based MAX phases 13 .…”