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

authors	Tkach, A; Okhay, O; Nuzhnyy, D; Petzelt, J; Vilarinho, PM
nationality	International
journal	MATERIALS
author keywords	perovskites; polar dielectrics; thin films; infrared spectroscopy
keywords	RAMAN-SCATTERING; SRTIO3; DEPENDENCE; DISPERSION; LOSSES
abstract	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.
publisher	MDPI
isbn	1996-1944
year published	2021
volume	14
issue	21
digital object identifier (doi)	10.3390/ma14216414
web of science category	9
subject category	Chemistry, Physical; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering; Physics, Applied; Physics, Condensed Matter
unique article identifier	WOS:000718389300001