Berlin 2018 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 27: Postersession KFM
KFM 27.9: Poster
Donnerstag, 15. März 2018, 15:00–17:00, Poster E
Polaron optical absorption in congruent lithium niobate from time-dependent density-functional theory — •Michael Friedrich1, W. G. Schmidt1, Arno Schindlmayr1, and Simone Sanna2 — 1Department Physik, Universität Paderborn, 33095 Paderborn, Germany — 2Institut für Theoretische Physik, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 16, 35392 Gießen
The optical properties of congruent lithium niobate are analyzed from first principles. The dielectric function of the material is calculated within time-dependent density-functional theory. The effects of isolated intrinsic defects and defect pairs, including the NbLi4+ antisite and the NbLi4+–NbNb4+ pair, commonly addressed as bound polaron and bipolaron, respectively, are discussed in detail. In addition, we present further possible realizations of polaronic and bipolaronic systems. The absorption feature around 1.64 eV, ascribed to small bound polarons [1], is nicely reproduced within these models. Among the investigated defects, we find that the presence of bipolarons at bound interstitial-vacancy pairs NbV–VLi can best explain the experimentally observed broad absorption band at 2.5 eV. Our results provide a microscopic model for the observed optical spectra and suggest that, besides NbLi antisites and Nb and Li vacancies, Nb interstitials are also formed in congruent lithium-niobate samples [2].
[1] O. F. Schirmer et al., J. Phys.: Condens. Matter 21, 123201 (2009).
[2] M. Friedrich et al., Phys. Rev. Materials 1, 054406 (2017).