Banca de QUALIFICAÇÃO: KETLIN MUCHINSKI GREMSKI

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : KETLIN MUCHINSKI GREMSKI
DATE: 25/09/2026
TIME: 09:00
LOCAL: Auditório PD
TITLE:

Study of defects in AMgF3 (A = K and Cs) compounds doped with Eu2+ and Eu3+

KEY WORDS:

Fluoroperovskites; Atomistic simulation; Charge compensation; Europium; Solution energy.

 

PAGES: 59
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

Europium-doped AMgF3 fluoroperovskites are candidate luminescent host matrices for scintillators and dosimetry, but the mechanisms by which the dopant is incorporated into the lattice remain undetermined, since spectroscopic techniques cannot discriminate between defect configurations that lower the site symmetry in similar ways. In this work we investigate, by classical atomistic simulation, the intrinsic and extrinsic defects of KMgF3 and CsMgF3, both pure and doped with Eu2+ and Eu3+ — two matrices that share the same structure type and the same octahedral cation and differ essentially in the size of the A site, which allowed us to isolate the effect of the available volume on the defect energetics. All calculations were carried out with the GULP code within the Born model for ionic solids, describing long-range interactions by the Coulomb potential evaluated through Ewald summation, short-range interactions by the Buckingham potential, and the polarisability of the F− ion by the shell model. We adopted the parameters of Sousa and Lima (2020) for the host interactions and the
potential of Rabone and De Leeuw (2006) for the Eu–F interaction. We started from the optimisation of the structures retrieved from the ICSD database, performed at constant pressure, and reproduced the experimental lattice parameters with deviations of +0.13% for KMgF3 and −0.23% for CsMgF3. We then established the radii of the concentric regions of the Mott-Littleton formalism through a convergence test, adopting 14 Å for region I and 18 Å for region IIa, a choice that entails residual deviations of 0.008 eV and 0.025 eV, one order of magnitude smaller than the energy differences between the reactions analysed. With this setup, we calculated the formation energies of the intrinsic defects — cationic and anionic Frenkel pairs, full and partial Schottky processes, anti-Schottky processes and antisite defects — and the solution energies associated with the incorporation of europium at both cation sites, considering charge compensation by cation vacancies, fluorine interstitials, antisite defects and their combinations, as well as configurations with simultaneous occupation of
both sites. Each reaction was evaluated in the unbound and bound configurations. Among the intrinsic defects, we obtained the Schottky reactions as the most favourable in both matrices, with 1.656 eV per defect in KMgF3 and 0.780 eV in CsMgF3, and the anti-Schottky reactions as the least favourable. As for the extrinsic defects, we found that the site preference depends on the oxidation state and on the matrix, and that the relationship between the two is reversed between the compounds: in KMgF3 the Eu2+ ion preferentially occupies the K+ site, with 1.000 eV per defect, and the Eu3+ ion the Mg2+ site, with 1.230 eV; in CsMgF3 the opposite occurs,
with Eu2+ at the Mg2+ site, with −0.264 eV, and Eu3+ at the Cs+ site, with 0.568 eV. We attribute this behaviour to the competition between size compatibility and charge compatibility, whose balance is shifted by the expansion of the MgF6 octahedron between the two matrices. We further observed that the bound configurations exhibit lower solution energies than the unbound ones in nearly all reactions and that, in Eu3+- doped CsMgF3, the binding energy of the cluster is large enough to reverse the stability order obtained for the isolated defects, so that an analysis restricted to the latter would lead to an incorrect site assignment. Finally, all
energies calculated for CsMgF3 turned out to be lower than those of the corresponding reactions in KMgF3, which we associate with the larger volume of the A site and with the lengthening of the Mg–F bond, from 1.99 Å to 2.11 Å.

 

 

COMMITTEE MEMBERS:
Presidente - 2264069 - HEVESON LUIS LIMA DE MATOS
Interno - 1979182 - EDWARD FERRAZ DE ALMEIDA JUNIOR
Interno - 1362906 - ADELMO SATURNINO DE SOUZA