Infrared dielectric dispersion of several fluoride perovskites

Measurements at room temperature of the infrared reflectivity, low-frequency dielectric constant (ε0), and optical index of refraction (n) have been made on KCoF3, KMnF3, and RbMnF3. The reflectivity data have been analyzed using Kramers-Kronig relations to obtain the dielectric dispersion from 50 cm-1 to 4000 cm-1. The frequencies of the three transverse optic (longitudinal optic) long-wavelength polar eigen-modes are 139 (168), 225 (293), 417 (500) cm-1 for KCoF3; 115 (143), 193 (268), 395 (479) cm-1 for KMnF3 and 113 (124), 197 (273), 369 (452) cm-1 for RbMnF3. ε0=7.35,8.28,7.6 and n=1.47,1.44,1.53 for KCoF3, KMnF3, and RbMnF3, respectively. Mode strengths and damping were also measured. Low-temperature reflectivity measurements on antiferromagnetically ordered KCoF3 were also performed. © 1967 The American Physical Society.