Efective infrared reflectivity and dielectric function of polycrystalline alumina ceramics

0474911 - FZÚ 2018 RIV DE eng J - Journal Article
Nuzhnyy, Dmitry - Petzelt, Jan - Borodavka, Fedir - Vaněk, Přemysl - Šimek, Daniel - Trunec, D. - Maca, K.
Efective infrared reflectivity and dielectric function of polycrystalline alumina ceramics.
Physica Status Solidi B. Roč. 254, č. 5 (2017), s. 1-8, č. článku 1600607. ISSN 0370-1972. E-ISSN 1521-3951
R&D Projects: GA ČR GA15-08389S
Institutional support: RVO:68378271
Keywords : alumina * ceramics * effective dielectric function * effective medium approximation * geometrical resonances * infrared reflectivity
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 1.729, year: 2017

Room-temperature infrared (IR) reflectivity, terahertz transmission and evaluated effective complex dielectric response of four polycrystalline alumina ceramics (corundum) with highly anisotropic grains in the IR range were determined. The spectra were compared with modelled spectra based on the known IR response of sapphire single crystal and Bruggeman and Lichtenecker models of the effective medium approximation (EMA). The results are extremely sensitive to the surface treatment (polishing), but do not depend on the grain size in the range of ∼0.3–1 μm and on the weak doping, needed for processing of optically transparent ceramics. As all the samples show similar grain shapes and topology, no measurable differences among the fully dense samples were observed. Agreement with the modelled spectra is reasonable, but shows a higher effective mode damping. A weak geometrical resonance was revealed near 500 cm−1, better described by the Bruggeman model. The small sample porosity up to 6.2% is revealed mainly as a reduced reflectivity above ∼650 cm−1, which produces weak losses in the high-frequency range above the TO phonon modes, better described by the Lichtenecker model.
Permanent Link: http://hdl.handle.net/11104/0271817