Polar Phonon Behaviour in Polycrystalline Bi-Doped Strontium Titanate Thin Films


Strontium titanate-based materials with ferroelectric or relaxor-like properties have drawn vast attention as polar dielectrics for electronics and telecommunications. Here, we study the lattice dynamics in sol-gel-derived Sr1-1.5xBixTiO3 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 SrTiO3 (ST) 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 ST. In heavily Bi-doped ST films, this mode displays no significant frequency variation with temperature from 300 to 10 K. The polar phonon behaviour of polycrystalline Bi-doped ST thin films is comparable with that of Bi-doped ST ceramics, which exhibit dielectric relaxations and harden soft-mode behaviour instead of the ferroelectric phase transition.



subject category

Chemistry, Physical; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering; Physics, Applied; Physics, Condensed Matter


Tkach, A; Okhay, O; Nuzhnyy, D; Petzelt, J; Vilarinho, PM

our authors


This article is supported by national funds, through FCT-Fundacao para a Ciencia e a Tecnologia, in the scope of the framework contract foreseen in numbers 4, 5 and 6 of article 23 of the Decree-Law 57/2016, of 29 August, and UID/EMS/00481/2019, UIDB/50011/2020 and UIDP/50011/2020 and by Centro 2020, through the European Regional Development Fund (ERDF), in the scope of the project CENTRO-01-0145-FEDER-022083, by Czech Science Foundation (Project No. 21-06802S) and by the MSMT Project SOLID21-CZ.02.1.01/0.0/0.0/16_019/0000760).

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