Resolution paracrystalline peak

Figure 8. Paracrystalline peak resolution. Corrected and smoothed equatorial trace of a PET fiber specimen resolved into three crystalline peaks, 010, 110, 100, a paracrystalline peak and the new best-fit background.

We will now consider three cases where satisfactory peak resolution was much more difficult to achieve. Case (a), a specimen of PET fibre used for texturising, having poorly defined crystalline peaks and possibly an additional peak due to an intermediate phase (11) case (b), a specimen from a range of PET fibres with different shrinkages (.12.), again an additional intermediate phase peak was a possibility case (c), cold drawn polypropylene fibres (13). an additional paracrystalline peak was most likely here. 

Resolution of polyester specimen PET 06 into three crystalline peaks, and three crystalline peaks and a paracrystalline peak... 

The three case studies outlined here give some indication of the worst difficulties that have been experienced with peak resolution, and have one factor in common the presence of an additional amorphous or paracrystalline peak was suspected in each case. All three optimization programs worked well when the input parameters were well chosen, but constraints were necessary in the more difficult cases and when broad peaks were present. Judicious choice of input parameters always speeds the ultimate solution and the use of BASELINE is most helpful. 

Figure 11. Good resolution with constrained optimization and addition of a paracrystalline peak. Corrected equatorial trace of a polypropylene fiber specimen cold drawn X-5.5. Total theoretical trace now comprised of realistic crystalline peaks 110, 040, 130, 111, 131, 041, and paracrystalline peak at 15.5°. Compare...

Resolution of cold drawn polypropylene specimens into crystalline and paracrystalline peaks... 

Peak resolution is usually easier if well chosen background parameters are input and if constrained optimization methods are utilised. Misleading results can be obtained if the constraints are too limited and tests with unconstrained optimization are desirable if at all possible. In particular, the possible presence of paracrystalline or intermediate phase peaks must be tested with extreme care in order to avoid ambiguity. It is not sufficient to have a good mathematical resolution alone, all peaks must be significant in crystallographic or structural terms. The incidental measurement of peak-area crystallinity is considered to be of secondary importance to the resolution of overlapping peaks. 

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See also in sourсe #XX -- [ ]

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