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Raman spectra of three polytypes of lead iodide (2H, 4H and 6H) have been investigated as a function of temperature at ambient pressure. The band assignments have been carried out on the basis of folding of 2H-PbIz phonon dispersion curves in the Brillouin zone. The temperature induced changes in the Raman spectra are interpreted in terms of an interpolytypic phase transformation (at 415 K) and photodecomposition at 470 K.

Articles you may be interested inSecondary neutron spectrum from 250-MeV passively scattered proton therapy: Measurement with an extended-range Bonner sphere system Med.Inelastic incoherent neutron scattering (lINS) cross sections have been measured for the recovered high-pressure phases of ice, ices II, V, VI, and IX (H 2 0) and ices II and IX (0 2 0) in the energy range from 2 to 140 me V at 20 K using the TFXA (time-focused crystal analyzer) neutron spectrometer on the ISIS pulsed neutron source at the Rutherford-Appleton Laboratory. The excellent resolution of the TFXA (less than 2%) covers the whole range of translational and librational modes for the ices investigated and enables us to identify the fine structures in their spectra. Hence a direct comparison between the amplitude-weighted phonon density of states derived from the experimental spectrum and from a lattice dynamic calculation is possible. The spectra from these polymorphic ices show many new features in the translational region, which are not visible using infared and Raman techniques. In the librational band region, the general features vary remarkably between phases. Thus, for instance, ice II, in which the protons are ordered, shows more structure in this region and has a sharper low-energy cutoff than do the other phases examined. The most significant observation is that the low-energy cutoff is characteristic of the phase. Relative to ice Ih, there is a shift of 4.3 meV for ice IX, of 8.8 meV for ice II, 8.6 meV for ice V, and 12.2 meV for ice VI. 6770 J. Chern. Phys. 94 (10). 15

A high-resolution survey of the 0.30-0.37-eV spectra, attributed to transitions at acceptor centers, obtained from several natural ^-type semiconducting diamonds at 80°K, is presented. Effects on the spectrum of destruction of the normal site symmetry (Td) by uniaxial compression are described. Hydrostatic stress has also been applied. Large spectral changes produced by uniaxial stress in the range 0-30 kbar have been analyzed in terms of the effective-mass theory of weakly bound electronic states, the lowest transitions being between quasihydrogenic s-^-like states. A coupling scheme here introduced for the p-like states is the opposite to that obtained for Si and Ge. Assignment of transitions has been made using theoretical band structures, results of reported spectral changes between 80 and 5°K, and the present stress spectra. Analysis of stress effects has been made using deformation-potential theory. The resulting potentials of D u v = +2.47, D u v = +1.63 eV are of the same sign as and similar magnitude to those of silicon.