RAMAN-SCATTERING IN LIQUID K-TE

Raman-scattering measurements from crystalline and liquid K0.12Te0.88 and K0.50Te0.50 semiconducting alloys are reported. The spectra of liquid K0.12Te0.88 are characterized by a single, weakly polarized band, markedly different from those obtained from pure liquid Te and bearing a greater similarity to the spectra reported for amorphous Te. The spectra of K0.50Te0.50 in the crystalline and liquid phases show remarkable similarities, confirming the presence of the Te2(2-) Zintl ion in both phases. Substantial softening of the symmetric stretching mode occurs relative to the equivalent mode in vapor and matrix-isolated Te2. This is most likely due to the charge transfer interaction with the K+ matrix. A comparison of structural data available for liquid and amorphous Te with those for liquid K0.12Te0.88 and K0.50Te0.50 indicates a transition to true 2-fold chainlike covalent bonding of Te in the liquid on addition of potassium. The importance of 2-fold bonding for the semiconducting behavior of Te-rich alloy systems in the liquid and solid states is discussed.