LATTICE VIBRATION-SPECTRA .80. EVALUATION OF IR REFLECTION SPECTRA - MODEL-CALCULATIONS AND EXPERIMENTAL-DATA OF MNCR2O4 SINGLE-CRYSTALS

The various evaluation procedures of IR reflection spectra, viz. Kramer-Kronig analyses (KKA), 3 parameter (omega(TO), phi, gamma) (3 PM), and 4 parameter (omega(TO), omega(LO), gamma(TO), gamma(LO)) oscillator-model calculations (4 PM), are compared. For the zone-centre phonon energies, the oscillator parameters omega(TO) and omega(LO) of 4 PM as well as the frequencies of the dielectric functions-epsilon" and -Im(1/epsilon), respectively (KKA, 3 PM), are recommended. The pole frequencies of the \epsilon\ functions yield too large TO/LO splittings, especially in the case of large damping of the phonons. In the case of asymmetric reststrahlen bands, the use of 4 PM with different damping constants-gamma for the TO and LO phonons is recommended. Computer simulations of the influence of the various oscillator parameters on the reflection spectra as well as the phonon frequencies of spinel-type MnCr2O4 are included.