Premium
Efective infrared reflectivity and dielectric function of polycrystalline alumina ceramics
Author(s) -
Nuzhnyy D.,
Petzelt J.,
Borodavka F.,
Vaněk P.,
Šimek D.,
Trunec M.,
Maca K.
Publication year - 2017
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201600607
Subject(s) - materials science , crystallite , ceramic , dielectric , spectral line , phonon , corundum , sapphire , infrared , anisotropy , terahertz radiation , grain size , range (aeronautics) , optics , mineralogy , condensed matter physics , analytical chemistry (journal) , optoelectronics , composite material , physics , chemistry , metallurgy , laser , chromatography , astronomy
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.