[Study of unusual infrared transmittance spectrum of the KBr pellet with a large amount of alpha-SiC powders].

In the spectroscopic experiments, additionally large extinction caused by the scattering in the vicinity of inherent absorption peaks of the measured sample granules can lead to a deviation of measured absorption peak from the corresponding inherent one, then an incorrect spectrum appears. This is just the Christiansen effect that we must take cares to avoid as much as possible. One of the measures we take is to use a small amount of sample material (less than 2%) when we make the pellets, for example KBr is the matrix. In an experiment, when a large (not small as usual) amount of alpha-SiC powder is dispersed into KBr powder, the resulted pellet has an infrared transmission spectrum with a sharp peak at the position of 1,052.33 cm-1. We find that this new phenomenon is very interesting, and looks contrary to the usual Christiansen effect, but can be explained with Lorentz dispersion model accurately together, so we call it reverse-Christiansen effect. Exactly at this frequency, the refractive indices of these two materials are equal, and absorption coefficients are very small. Also, it is very useful for making a new type of band-pass filter or determining the refractive indices of some materials correctly, etc.