/1. D. P. Matheis and R. L. Snyder,
/``X-ray Powder Diffraction Analysis of the Incommensurate Modulated
/Structure of \bittot,'' {\it Powder Diffraction} {\bf 9} 28-37 (1994).
/
/modified the Wiles Young Rietveld code to handle modulated structures. We
/also modified the NBS*LSQ lattice parameter code to refine the modulation
/vectors. Both codes are available by anonymous FTP from XRAY.ALFRED.EDU
/
/2. S. A. Howard and R. L. Snyder, ``The Use of Direct Convolution
/Products in Profile and Pattern Fitting Algorithms I. Development of
/the Algorithms,'' {\it J. Appl. Crystallogr.} {\bf22}, 238-243 (1989).
/(also see: \item R. L. Snyder, ``Analytical Profile Fitting of X-ray Powder
/Diffraction Profiles in Rietveld Analysis,'' Chap 7, p. 111-131,
/\underline{The Rietveld Method} Oxford University Press (1993))
/
/developed a general profile fitting code called SHADOW, which will exactly
/fit most profiles no matter how assymetric, the profile. It permits
/deconvolution of the specimen profile function S from the profile function
/and models S with size and strain broadening. It does not have an explicit
/stacking fault model in its current form. The public domain version is
/also available from the same FTP.
Sorry but
this looks like promotion rather than information. Information is in the
"Powder Diffraction Program Information 1990 Program List" prepared by
D.K. Smith and S. Gorter (J. Appl. Cryst. 24, 369-402, 1991) that everybody
in this group certainly know (an update is announced?). In this program list,
SHADOW is said to perform "Profile fitting - decomposition". The complete
list of programs classified under this title is : ABFfit, AUTOPEAK, CUVFIT,
DIFFRACT-AT/FIT, DOREES, FIT, KET,KETA, LAT1, LSQPROF, MicroSHADOW, PEAK,
Pi'oPiliPa'a, POWDER, POWDERPATTERN, PROFAN, PROFAN/PC, PROFIT, PRO-FIT,
REGION, SCRAP, SHADOW, TOFMANY, TXTPVGT, XRAYL..... Most of these programs
are able to fit perfectly a powder pattern with R<2% and some are able to
suggest size/microstrain parameters.
About SHADOW that "will exactly fit most profiles no matter how assymetric,
the profile," the user's manual gives the following information :
---------------------------------------------------------------------------
---------------------------------------------------------------------------
C *** PROGRAM: SHADOW (SHADOW00) - PATTERN ANALYSIS PROGRAM
C *** VERSION: 860822 (YYMMDD)
C *
...................................
...................................
_
Application of the Pattern Asymmetry Factor
The pattern asymmetry factor can optionally be applied to every
profile in the segment of pattern being refined. This asymmetry
factor is the multiplicative function given by Rietveld{7}. The form
of the function is:
P s ( theta(k) - theta(i) ){2}
A}i,k{ = 1 - ------------------------------
tan( theta(k) )
where theta(k) == the kth Bragg diffraction angle
theta(i) == the angle of the ith point in the profile
P == the asymmetry parameter under refinement
s = 1 for theta(k) - theta(i) > 0
= 0 for " " " " " = 0
= -1 for " " " " " < 0
The asymmetry factor is applied to each point in all the profiles as:
I(i)}k{ = I(i) * A}i,k{
...................................
...................................
-----------------------------------------------------------------------
-----------------------------------------------------------------------
I am afraid that information about 2D disorder in graphite intercalates
will never be obtained by such a treatment of the asymmetry. May be there
is a more recent SHADOW version ?
Personally I am now intrigued by Pi'oPiliPa'a in the above program list...
Any information about this program ?
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Armel LE BAIL ! some french proverbs :
Laboratoire des Fluorures !
Universite du Maine ! "De la discussion jaillit la lumiere"
72017 Le Mans Cedex !
FRANCE ! "Mefiance est mere de surete"
!
armel@ONE.univ-lemans.fr ! "L'air ne fait pas la chanson"