Raman in-phase phonon

Fig. 79. Raman in-phase phonon frequency vs. x. Average values from 5-10 erystallites at each composition. Compare with fig. 65 showing the individual measurements. The onset of the abrupt softening of the phonon is elearly seen at the transition stoichiometry (x=6.95). After Poulakis et al. (1996), Palles (2000) and Palles et al. (2000a).

Raman in-phase phonon fi equency indicates a single phase. The stoichiometry of the 3 o superstructure is x = 6.66 (small asterisk in lower part of fig. 110). x = 6.66-6.75... 

Raman in-phase phonon fi equency indicates a two-phase region, possibly (3uo + 5ao), between the 3 o and 5 o compositions. 

Raman In-phase phonon Irequency shows a single phase behavior. The composition of the 5 o superstructure would be x = 6.80 (fig. 111). 

Raman In-phase phonon Irequency two-phase regions. The ideal stoichiometry of the 8flo lies with 6.875 inside this range. In case of actual superstructures this would mean disorder vacancies in the chains shifting the appearance of the superstructures at higher compositions (sect. 5.1.1). From the sequence, it could be a miscibility gap 5ao-l-8ao (fig. 111). 

Raman In-phase phonon Irequency, transition Irom two-phase region to a single phase region. Analogy to a phase boundary between 5uo + 8uo and 8ao superstructures... 

Raman In-phase phonon indicates the stability region of the ouerdoped phase A (fig. 110). 

Fig. 110. In-phase phonon frequency (Raman shifts) vs. oxygen content x for 6.40

Raman Both apex and in-phase phonons show smaller changes of slope, but much less abrupt and significant than at x = 6.20. 

Raman The statistics of the microcrystallites indicate the existence of two steps of the in-phase phonon (02-03) frequency (one between 6.40-6.43 and another at 6.50) nearly overlapping with the range of the 2ao chain superstructure (fig. 110 and sect. 5.5.2). 

Raman The apex phonon frequency becomes independent of the oxygen content (fig. 61). The in-phase phonon indicates a phase boundary (transition). From stoichiometry it could be the boundary between the two-phase region (3ao + 5oo), and the 5 o superstructures (fig. 110), (sect 5.4.2). 

Raman RT In-phase phonon possibly indicates a two-phase region. Analogy with 8uo+A, the overdoped phase (fig. 111). 

The elementary excitations mentioned so far are not related in any special way to the solid state and will therefore not be treated in this article. We will discuss here the following low-lying quantized excitations or quasi-particles which have been investigated by Raman spectroscopic methods phonons, polaritons, plasmons and coupled plasmon-phonon states, plasmaritons, mag-nons, and Landau levels. Finally, phase transitions were also studied by light scattering experiments however, they cannot be dealt with in this article. 

Some variations in the phonon density of states (DOS) in translational and librational mode regions were studied by inelastic incoherent neutron scattering (IINS) and also studied by molecular dynamics (MD) . For the spectroscopic studies of phonons in XI phase, only a few studies have been reported . We have reported several studies on Raman spectra in the proton ordered XI phase However, detailed mode assignment has not been made successfully yet because of the difficulties to get a single crystal which undergoes the Ih-XI transition with enough transparency suitable for Raman measurement. 

Raman scattering as a function of nonstoichiometry — II. Softening of the in-phase 02,03 phonon... 

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