Far Infrared Reflection Spectra and Lattice Vibrations of CsNiCl3 Crystal

The frequencies of the transverse (TO) and longitudinal (LO) modes of the infrared active vibrations of the crystal CsNiCl3 were obtained from the polarized far infrared reflection spectra. The polarized Raman spectra were also measured. The calculation of the TO and LO frequencies near the center of the Brillouin zone was made on the basis of a rigid ion model which includes effective ionic charges and interionic repulsive force constants. A set of potential constants and effective ionic charges were determined from the observed values of the TO and LO frequencies and Raman frequencies using the least-squares method. The short-range force constant associated with the nickel ion to the chlorine ion indicates that some amount of covalent character is included in this bond.