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A method for the determination of infrared optical constants from reflectance measurements on powdered samples

A method for determining the infrared dielectric constant function of an isotropic material from measurement of the reflectance from powdered samples has been implemented. The method is based on an expression for the average dielectric constant of a heterogeneous system, which shows percolation features. The results obtained through the use of this method compare well with published results from single-crystal reflectance data, and show that damping factors in powders are moderately higher than those measured for single crystals. The method works best if samples are made of small microparticles (less than 2 mu m), pressed to filling factors less than 0.6. Some precaution should be exercised with plastic ionic substances. The method can be used to determine the dielectric constant of a large number of compounds that cannot be obtained as centimetre-sized single crystals.