Berlin 2024 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 9: KFM Poster Session
KFM 9.39: Poster
Montag, 18. März 2024, 18:00–20:00, Poster E
Polarized absorption spectroscopy of optically gated small polarons in thermally reduced lithium tantalate — •Anton Pfannstiel1, Tobias Hehemann1, Simone Sanna2, Nils Schäfer2, Yuriy Suhak3, Holger Fritze3, and Mirco Imlau1 — 1Inst. Physics, Barbarastr. 7, Osnabrück Univ., Osnabrück — 2Dept. of Physics, Heinrich-Buff-Ring 16, Justus Liebig University , Giessen — 3Inst. of Energy Research and Physical Technology, Am Stollen 19 B, Clausthal University of Technology, Goslar
The optical absorption features of small bound polarons in lithium tantalate are characterized by a broad (∼ 1.0 eV) band at ∼ 2.1 eV and are likely assigned to TaLi4+/5+ antisites. Also, the presence of interstitial Tai3+ defect centers is discussed in literature, but experimental evidence for respective small polaron formation is missing in literature, so far. We have adressed this question by polarized absorption spectroscopy of optically gated small polarons in thermally reduced LiTaO3 (congruently melting composition). Upon exposure to gating light (λ=488 nm) and polarized detection of the absorption change at T=80 K, we discovered that the NIR absorption feature is due to a superposition of two individual bands peaking at 1.6 eV and 2.1 eV, respectively. These findings are found in agreement with the energies estimated for TaLi4+ and Tai4+ sites by density functional calculations. An alternative interpretation that is based on the particular structural distortion of the defect environment in the polaron state is discussed. Financial support by the DFG is acknowledged (project IM 37/12-1; SU1261/1-1; FR1301/42-1; SA 1948/3-1; research unit FOR 5044).
Keywords: lithium tantalate; polaron; optical absorption; thermal reduction