Lattice Vibrations of Magnetic Semiconductor Chalcogenide Spinels, Hg_x Zn_1−x Cr₂ Se₄

Abstract

The infrared absorption spectra due to the lattice vibrations and the intrinsic transitions in mixed crystals, Hg_x Zn_1−x Cr₂ Se₄ have been studied for x=0∼1. Four absorption bands of fundamental lattice vibrations were observed in pure crystals for x=0 and 1, and five intense absorption bands were observed in mixed crystals. The concentration dependence of the three bands shows one-mode type behaviour, whereas that of the other two bands shows two-mode type behaviour. In addition to these bands, a few weak absorption bands were found near the two-mode type absorption bands.
The concentration dependence of lattice vibration frequencies is interpreted by a simple model which takes into consideration the six force constants. The main features of the model are that the two force constants and the mass relating to the Hg site are varied continuously with the Hg concentration and that two kinds of clusters are taken into consideration.
For these crystals, the positions of the fundamental absorption edges shift linearly toward lower energy side with the Hg concentration, and the lattice constants determined from X-ray analysis in mixed crystals obey Vegard’s law.