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DF: Fachverband Dielektrische Festkörper

DF 11: Small Polarons in LiNbO₃

DF 11.4: Vortrag

Mittwoch, 18. März 2015, 10:30–10:50, EB 133C

Polarons trapped at Ti centres in LiNbO₃ — •Gábor Corradi — Wigner Research Centre for Physics, Budapest, Hungary

Ti in LiNbO₃ is a well known dopant on Li-site changing the refractive index which can be used e.g. for producing waveguiding surface layers by Ti in-diffusion. The index change can be attributed to the existence of 3d-type Ti^4+/3+ donor polaron states in the gap which are similar to antisite Nb^5+/4+ polaron states with homologous 4d-type electron structure, the Ti level being only 0.11 eV deeper than the Nb^5+/4+ one. Mg co-doping can be used, similarly to the case of Nb(Li) antisites, also for the elimination of Ti(Li) centres, resulting in the appearance of Ti on Nb site. All four trapped-polaron d1 centres Ti(Li)³⁺, Ti(Nb)³⁺, Nb(Li)⁴⁺, and Nb(Nb)⁴⁺ show absorption bands due to charge transfer to states inside the conduction band with slightly stronger local admixture for Ti than for Nb. As shown by the analysis of the EPR spectra, all four centres are subjected to Jahn-Teller distortion with increasing JT energy as one goes from Nb⁴⁺ to Ti³⁺ centres, or from Li to Nb substitution. The systematically shifted properties can be used for fine tuning polaronic effects by Ti and Mg doping and appropriate levels of reduction treatments.