Measurement of Infrared Spectra of Dense Ceramics by Specular Reflectance Spectroscopy

It is shown that high-quality IR specular reflectance spectra can be obtained from polished surfaces of dense ceramics. The reflectance spectra can be deconvoluted by the Kramers-Kronig transformation to yield absorption spectra or the real and imaginary parts of the dielectric function. IR line shapes and peak wavenumbers are comparable to single-crystal data providing that the particle size is small compared with the IR wavelengths of interest. For noncubic structures, the spectra are a superposition of polarization components. Modes separated by less than a bandwidth are merged into a single band, thus limiting the resolution of the measurement procedure. Grain size effects were modeled using the spectra of single-crystal and polycrystalline quartz as an example.