Far-infrared absorption spectra of CaF2-YF3-NdF3 solid solutions

The transmission and reflection spectra of the (CaF2)(1-x-y)-(YF3)(x)-(NdF3)(y) crystals with x = 0-0.15 and y = 0-0.16 were measured in the far-IR region (4-1000 cm(-1)) within the temperature range of 80-1100 K. The transition from the ordered system (x = y = 0) to the disordered system (x = 0.15 and y = 0.16) results in the tenfold increase in absorption in the frequency range between 4 and 150 cm(-1). The wide-range frequency and concentration dependences of absorption were obtained. A sharp increase in the absorption coefficient was observed with increasing temperature; the onset temperature of this increase is lowered from 1000 K for the sample with x = 0.06 and y = 0.003 to 700 K for the sample with x = 0.15 and y = 0.16.