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DMC: COLD NEUTRON POWDER DIFFRACTOMETER
Refinement of DMC data using FULLPROF
Fullprof Manual (pdf)
Fullprof recognizes the DMC data format (Ins=8).
Best fits are achieved using profile function 4 (Npr=4) in Fullprof. Besides U,V and W
this peak shape requires 4 additional parameters (Shape1, X, Y, Shp1). Click here for an example:
These parameters are instrument parameters and should not be refined. At λ = 2.567 Å we
get Shape1=0, X=0.3025, Y=0.3365, Shp1=0.00776. The parameters U,V and W depend on the sample and must
be refined. Possible starting values at 2.567 Å are 0.92, -0.63, 0.20. See the table below for the list of peak shape parameters at other wavelengths.
It is advised to set Wdt, the cut-off of the peak profile tails, to a small number, e.g. 3.
Example of a refinement:
pcr file ,
data file ,
plot
You may as well use other profile functions, e.g. peak shape function 7 (Npr=7, see Fullprof manual). This will
lead to quite similar values of the refined structural or magnetic parameters but with somewhat
larger errors.
Table: Peak shape parameters for peak shape function 4 (Npr=4)
| Wavelength |
Shape1 |
X |
Y |
Shp1 |
U 3) |
V 3) |
W 3) |
| 2.45 Å |
0 |
0.2849 |
0.3657 |
0.00787 |
0.94 |
-0.57 |
0.18 |
| 2.57 Å |
0 |
0.3025 |
0.3365 |
0.00776 |
0.92 |
-0.63 |
0.20 |
| 3.80 Å 1) |
0 |
0.3443 |
0.3156 |
0.00583 |
0.75 |
-0.81 |
0.35 |
| 3.80 Å 2) |
0 |
0.4631 |
0.3970 |
0.00477 |
0.48 |
-0.33 |
0.20 |
| 4.20 Å 1) |
0 |
0.3620 |
0.3385 |
0.00536 |
0.55 |
-0.58 |
0.35 |
| 4.20 Å 2) |
0 |
0.4381 |
0.4092 |
0.00457 |
0.38 |
-0.15 |
0.17 |
| 4.50 Å 2) |
0 |
0.4386 |
0.3904 |
0.00437 |
0.31 |
-0.12 |
0.18 |
1) short distance, 2) long distance, 3) possible starting values for the refinement
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