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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 15: Postersession KFM

KFM 15.27: Poster

Donnerstag, 19. März 2020, 16:00–18:30, P2/1OG

Point defects in KTP calculated from first principles — •Adriana Bocchini, Sergej Neufeld, Uwe Gerstmann, and Wolf Gero Schmidt — Department Physik, Universität Paderborn, 33095 Paderborn, Germany

The unique combination of optical and electric properties of potassium titanyl phosphate (KTiOPO4, KTP) combined with its excellent thermal stability enables a wide range of applications, e.g. for second harmonic generation (SHG) [1]. However, KTP is prone to photochromic damage, so-called gray tracking. Microscopically, the reduction of Ti atoms has been suggested to cause gray tracking: electron paramagnetic resonance (EPR) signatures assigned to Ti3+ in intrinsic defect centers were detected in crystals affected by gray tracks [2].

In the present work we explore point defects in KTP, namely O and K vacancies and H interstitials, using density-functional theory. Particular attention is given to the charge redistribution inside the cell [3]. It is found that the impact of K vacancies on the properties of KTP is nearly neglectable, while O vacancies and H interstitials cause a charge reduction of the neighboring Ti atoms. In addition, both defects lead to similar P atom hyperfine splittings which qualitatively reproduce the experimental data [4]. These findings imply O and H defects to play a significant role in the formation of gray tracks.

[1] M. Roth, Springer Handbook of Crystal Growth (2010).

[2] M. G. Roelofs, J. Appl. Phys. 65, 4976 (1989).

[3] A. Bocchini et al., J. Phys.: Condens. Matter 31 385401 (2019).

[4] S. D. Setzler et al.., J. Phys.: Condens. Matter 15, 3969 (2003)