Polaritons In The Ternary Mixed Crystals

Long-wavelength transverse optical-phonon in ionic crystals (or polar crystals) can couple to transverse electromagnetic waves, and they can form a kind of compound elementary excitations. This kind of elementary excitations are known as polaritons. In this paper, we begin with the mechanism of the generation of polaritons, then we have calculated and discussed the basic properties of polaritons in the ternary mixed crystals(TMCs) by utilizing the formed thinking and the successful model: MREI model of binary ionic crystals.After calculating we can get some important results for TMC: AxB1-x.C as follows:The frequencies of polaritons have no relation to the direction of the wave vectors, and they change with the magnitude of the wave vectors only. In this situation, there are four characteristicfrequencies of the lattice vibration. They are TOAC, TOAC, LOBC and TOBC. When the wavevectors are very small, polaritons of low frequency branch take on clearly electromagnetic property, and polaritons of high frequency branch assume clearly mechanic property. The frequency of highbranch equal to when wave vectors vanish. By contrast, when the wave vectors areconsiderably large, polaritons of high frequency branch take on clearly electromagnetic property, while polaritons of low frequency branch assume clearly mechanic property, and when the wavevectors are vary large, the frequencies of low branch tend to TO2If we pay attention to the middle frequency branch, we can find it easily that when the wave vectors are very small, its frequency tend to LO2, and when the wave vectors are considerablylarge, they tend to TO1.So, there are two gaps in the sketch of the polariton dispersion relation for general ternary mixed crystals. One of them is from TO1 to LO1 , the other from TO2 to LO2. One may find this in the experiments.