Banca de QUALIFICAÇÃO: GUILHERME RIBEIRO PORTUGAL

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : GUILHERME RIBEIRO PORTUGAL
DATA : 11/03/2020
HORA: 14:00
LOCAL: a ser definido
TÍTULO:

Understanding intrinsic NaTaO₃ structural and electronic properties: a theoretical approach from infinite surfaces to nanostructures aiming water-splitting photocatalysis

PÁGINAS: 50
RESUMO:

Sodium tantalate (NaTaO₃) structures have been considered one of the most promising materials to conduct water-splitting photocatalytic reactions. Understanding the structural and electronic behavior of atomically distinct surfaces is of fundamental importance to elucidate the relationship between reactivity and different terminations. Cubic and orthorhombic surfaces of NaTaO₃ in a range of structures were simulated through ab initio Density Functional Theory calculations. A first broader systematic investigation of infinite slabs pointed to the orthorhombic NaTaO-terminated surface as the best candidate to perform photocatalytic reactions. The cleavage-induced TaO₄ arrangements, although more energetically expensive, allowed polyhedral rotation and distortion during structural reconstruction. Well-localized Ta energy states were introduced inside the bandgap, and happen to be coherently aligned with the water oxidation potential. In nanostructures, a similar behavior was observed for cubic (110) oriented ultrathin films and later confirmed when analogous KTaO₃ films were investigated for comparison. Intrinsically, surface Ta shallow states emerged again into the bandgap since the (110) cleavage breaks the octahedral symmetry to create TaO₄ units. Removal of ligands along the x-y axis stabilizes d_x²_-y² orbitals, which decreased in energy due to lower electrostatic repulsion. Such stabilization was maximized when biaxial tensile increased the TaO₄ planarity towards a square planar symmetry. Accordingly, the corresponding electronic levels moved further into the bandgap. Conversely, compressive biaxial strain intensified electrostatic repulsion, closing the TaO₄ tetrahedra and shifting surface states to higher energy zones. The reported strain-driven modulation might be useful for different applications, as photocatalysis and spintronics. Regarding nanowires, chemically different facets affected structural and electronic properties even more prominently. Besides half-metallicity, the NaO-terminated wire showed unoccupied down O 2p levels located above its valence band due to severely reduced coordination of its edges. NaTaO-terminated wires have, similarly to the what have been found for infinite slabs and ultrathin films, surface TaO₄ units that became more planar upon structural reconstruction and introduced occupied Ta 5d states below their conduction band. The aforementioned common characteristics that have been observed from infinite slabs to nanowires have led to a better understanding of possible reasons why NaTaO₃ stands out intrinsically in photocatalytic terms, and can therefore guide experimental studies and future investigations on the subject.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1671688 - ANDRE SARTO POLO
Membro Titular - Examinador(a) Interno ao Programa - 2218228 - LUANA SUCUPIRA PEDROZA
Membro Titular - Examinador(a) Externo ao Programa - 1309493 - PEDRO ALVES DA SILVA AUTRETO
Membro Suplente - Examinador(a) Interno ao Programa - 1734908 - FABIO FURLAN FERREIRA
Membro Suplente - Examinador(a) Interno ao Programa - 1957564 - CEDRIC ROCHA LEAO
Membro Suplente - Examinador(a) Externo ao Programa - 1765425 - MARCIO GUSTAVO DI VERNIERI CUPPARI