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O: Fachverband Oberflächenphysik

O 97: Focus Session: SrTiO₃: A Versatile Material from Bulk Quantum Paraelectric to 2D Superconductor II (joint session TT/KFM/MA/O)

O 97.6: Talk

Thursday, March 21, 2024, 16:15–16:30, H 0104

Polar phonon behaviour in polycrystalline Bi-doped strontium titanate thin films — •Oleksandr Tkach¹, Olena Okhay², Dmitry Nuzhnyy³, Jan Petzelt³, and Paula M. Vilarinho¹ — ¹Department of Materials and Ceramic Engineering, CICECO, University of Aveiro, Aveiro, Portugal — ²TEMA-Centre for Mechanical Technology and Automation, Department of Mechanical Engineering, University of Aveiro, Aveiro, Portugal — ³Institute of Physics of the Czech Academy of Sciences, Prague, Czechia

Among strontium titanate (STO) based materials, Bi-doped STO have been intensively studied as for dielectric as for resistance-switching memory and thermoelectric applications. Here, we enhance the dielectric characterisation by a lattice dynamics study of sol-gel-derived Sr_1−1.5xBi_xTiO₃ thin films with x = 0.0053 and 0.167, deposited on Al₂O₃ substrates, using a variable-temperature far-infrared spectroscopy in a transmittance mode. Bi doping, known to induce a low-frequency dielectric relaxation in STO ceramics and films, due to off-centre dopant ion displacements generating electric dipoles, is shown to affect the polar phonon behaviour of thin films. We show that in weakly Bi-doped films, the low-frequency polar TO1 mode softens on cooling but less than in undoped STO. In heavily Bi-doped STO films, this mode displays no significant frequency variation with temperature from 300 to 10 K. The polar phonon behaviour of polycrystalline Bi-doped STO thin films is comparable with that of Bi-doped STO ceramics, which exhibit dielectric relaxations and harden soft-mode behaviour instead of the ferroelectric phase transition.

Keywords: perovskites; polar dielectrics; doping; lattice dynamics