A DFT investigation of the role of oxygen vacancies on the structural, electronic and magnetic properties of ATiO₃ (A = Mn, Fe, Ni) multiferroic materials

Abstract

In order to achieve deep insight into the multiferroic behavior and electronic properties of intrinsic oxygen vacancies in ATiO3 (A = Mn, Fe, Ni), first-principles calculations based on hybrid density functional theory were carried out for bulk and non-polar (110) surface models. We found that the formation of an oxygen vacancy is accompanied by structural and electronic disorders in the constituent clusters of [TiO6] and [AO6] in ATiO3, that become [TiO5] and [AO5], respectively. This perturbation contributes to the generation of intermediary energy levels in the band gap region, thus narrowing the required excitation energy. In addition, the remaining electrons are mainly trapped in the empty 3d orbitals of the Ti cations neighboring the oxygen vacancy, generating [TiO5]' (3d1) that mediates an antiferromagnetic to ferromagnetic transition in MnTiO3 and FeTiO3 materials. In particular, MnTiO3 surfaces show exposed [TiO4]' species that are responsible for its half-metallic behavior. The present work provides compelling evidence that controlling oxygen vacancies can be a valuable strategy to tailor the multiferroic properties of ATiO3 materials.

A broad theoretical investigation of R‐3, R3c, and R‐3c polymorphs of FeCrO3

“…As a consequence, the spin‐orbit coupling (SOC) can be neglected because the spin symmetry is decreased/removed from the coupling effect. The reliability of such interpretation is indicated by the results reported in the literature and its agreement with experimental results 52‐55 …”

“…Hence, the cleavage energy for relaxed surfaces ( ) was obtained from Equations and . This methodology is very representative and has been successfully applied to investigate the surface properties of several materials 54,55,63‐66 . Thus, the obtained surfaces for LNO‐, ilmenite‐ and corundum‐type are Cr–O 3 –Pb–Ni–O 3 –Fe [18 layers], Fe–O 3 ‐Cr 2 –O 3 –Fe [6 layers], and Fe–O 3 –Cr–Fe–O 3 – Cr [4 layers] respectively. …”

“…The reliability of such interpretation is indicated by the results reported in the literature and its agreement with experimental results. [52][53][54][55] In this work, the Ilmenite (R-3), Lithium Niobate (LNO-R3c), and corundum (R-3c) structures were evaluated through periodic models based on crystallographic information for FeCrO 3 . [24][25][26] In such models, the Fe and Cr atoms are magnetic due to the existence of unpaired electrons.…”

“…This methodology is very representative and has been successfully applied to investigate the surface properties of several materials. 54,55,[63][64][65][66] Thus, the obtained surfaces for LNO-, ilmenite-and corundum-type The magnetic properties of each surface were evaluated by a similar approach to that applied top the bulk magnetism. However, the Ising Hamiltonian limitation prevents their application to study of materials with a high number of non-equivalent positions, as observed on solid-state surfaces cut.…”

Bridging experiment and theory: Morphology, optical, electronic, and magnetic properties of MnWO4

“…This procedure has been performed to obtain the complete set of morphologies of different materials based on the Wulff construction and the values of E surf and to investigate the magnetic and multiferroic properties of different materials [19,37,[41][42][43][44][45][46][47][48], in addition to pathways connecting the different morphologies. The energy (E pol ) and band gap energy (E poly gap ) of the polyhedron were calculated by assuming the contributions from each surface to the morphology (C (hkl) i…”