At 07:22 26/08/2001, you wrote:
>Who knew the atom fractional coordinates of Li2SnO3?
From ICSD-for-WWW: http://www.fiz-karlsruhe.de/fiz/products/icsd/
Hodeau,JL. Marezio,M. Santoro,A. Roth,RS. (1982) Journal of Solid State
Chemistry 45 170-179
Neutron Profile Refinement of the Structures of Li2 Sn O3 and Li2 Zr O3
N *-Li2SnO3-[C12/C1]-Hodeau J L, Marezio M, Santoro
C 5.2889 9.1872 10.0260 90. 100.348 90.
S GRUP C 2/C
A Sn1 0.00000 0.41800 0.25000 0.20000 1.00000
A Sn2 0.00000 0.75000 0.25000 0.20000 1.00000
A O1 0.13870 0.26100 0.13390 0.48000 1.00000
A O2 0.11180 0.58530 0.13400 0.19000 1.00000
A O3 0.13430 0.90780 0.13220 0.15000 1.00000
A Li1 0.23100 0.07300 0.99940 1.50000 1.00000
A Li2 0.25000 0.25000 0.50000 1.50000 0.82000
A Li3 0.00000 0.08300 0.25000 1.50000 0.78800
>1.If there are three or more atoms in the same
>site(e.g.,LiNi1-x-y-zCoxMgyTizO2, how to set the constraints and refine
>their fractions?
Physically, you can only determine the total scattering power of the site.
In the case of 2 atoms sharing a site, some programmes allow you to set
code words such that the total atomic occupancy number remains fixed - a
decrease in the occupancy of one atom is coupled to an increase in the
occupancy of the other such that this condition is satisfied. But you can
also just refine the effective scattering power of a single atom at that
site and apply this constraint at the end. If you have 3 atoms, again you
can just refine the scattering power of a single atom at that site, and
then hopefully use additional information to estimate the amounts of the
different elements - such as the total amounts of the 3 elements in the
sample... You could also do a joint X-ray-neutron refinement, which will
give you additional information because of the different scattering powers
for X-rays and neutrons.
>2.When setting atoms' valences and fractions,whether is the principle of
>charge neutrality considered?
The "valence sum" for a particular site is obtained from simple formulae
involving the distances from that site to all "bonded" atoms, as discussed
recently in this forum. Again only one number can be obtained for each atom
site, but the parameters in the "valence sum" formula depend somewhat on
the element and oxidation state of the occupants of the site. In the case
of multiple occupancy of a site, you can try using the sum calculated from
the fractional occupancies. But remember that this kind of calculation is
only a check that the structure is "reasonable". eg if you find bond
lengths and valence sums consistent with Li+ then you can be pretty sure
that the site is not occupied by much Co3+ :-)
>3.How can I copy the plots of dmplot or GSAS to the files of Word2000?
You can paste various graphic formats into Word. If your plotting programme
does not allow you to save the plot in a suitable format, you can use a
screen capture programme such as "PrintKey" for Windows to capture the plot
area: http://www.geocities.com/~gigaman
Alan.
Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]> fax direct (33) 4.76.20.76.48
tel (33) 4.76.20.72.13 (or .26 Mme Guillermet)
http://www.ill.fr/dif/AlanHewat.htm
