Phonon dynamics of ceramic PbSc₀.₅Ta₀.₅O₃

Spencer, Stephen (2016) Phonon dynamics of ceramic PbSc₀.₅Ta₀.₅O₃. Masters thesis, Memorial University of Newfoundland.

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Abstract

This work aims to compare the optical and acoustic phonon properties between ceramic PST and previously studies crystalline PST, as such a study has never been performed. If easily fabricated ceramic PST has similar phonon properties to crystalline PST, it can serve the same purpose in industrial applications. Inelastic light scattering experiments were performed on lead scandium tantalate to probe acoustic and optical phonons in the material. Brillouin scattering experiments were performed at room temperature using a 180ﾟ backscattering geometry. Two peaks were observed in spectra, at shifts of ~25 GHz and ~44 GHz, which were independent of angle of incidence. These peaks were determined to be due to the longitudinal and transverse bulk modes, respectively. Using the average frequencies of these peaks, the velocities of these modes were calculated, and subsequently elastic constants c₁₁, c₄₄, and c₁₂ were calculated. Brillouin light scattering experiments performed on a lead scandium tantalate ceramic with a 40 nm aluminum coating yielded an additional Brillouin peak that was not observed in uncoated experiments which may be due to the Rayleigh surface mode. Raman light scattering experiments were performed on lead scandium tantalate at room temperature and temperatures ranging from 200ﾟC to 1200ﾟC. Four Raman peaks were observed at room temperature, at shifts of ~45 cm⁻¹ ~220 cm⁻¹, ~350 cm⁻¹, and ~825 cm⁻¹, the strongest of which determined to be due to an F₂g mode. At high temperatures, the intensity of the latter three peaks became significantly weaker, with the F2g mode frequency increasing at temperatures ranging from 200ﾟC to 550ﾟC. At temperatures ranging from 550ﾟC to 900ﾟC, there was very little change in the position of the peaks between spectra. For temperatures above 900ﾟ, only the F₂g mode was observed. In these spectra, the peak frequency shift was higher, and its intensity significantly decreased compared to other high temperature spectra.

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