Pb1-xMnxTe and PbTe1-xSx compounds and their optical properties

Pb1-xMnxTe crystals were obtained by the Bridgman method and PbTe1-xSx crystals were grown by the vapour–liquid–solid technique. The tructural properties of Pb1-xMnxTe (x £ 0.10) and PbTe1-xSx (x £ 0.05) were observed by X-ray powder diffraction analysis. The optical properties were studied by Raman spectroscopy as a function of temperature. Measurements on these samples of different composition gave information about the Mn and S position in the lattice (off-centering), their clustering and ordering, as well as of the influence of these processes on the crystal structure and properties. The model of phonon behaviour based on the Random Element Isodisplacement model was applied, and it was found that the phonons in PbTe1-xSx show a two-mode behaviour (each TO-LO mode pair of the end members degenerates to an impurity mode), while the Pb1-xMnxTe optical phonons have a ntermediate one-two-mode behaviour (the LO-mode frequency shifts continuously from PbTe to MnTe, while the other modes resemble the two-mode case).