We are new users of Rietveld programs; we use it with mixed oxides of
iron and rare earth. We have a Philips PW 1710 diffractometer with
automatic divergence slit, a 0.2 mm receiving slit and a 1=BA scatter slit
(we convert the ADS data to fixed divergence slit using a formula supplied
in the Philips documentation). We use RIETAN (supplied by Dr. Izumi) and
LS1 (supplied by Dr. Lutterotti) programmes to fit the data, but we obtain
always very high values of the termal parameters (between 2 and 6,=20
sometimes higher).=20
I would like first the best conditions for the diffractometer work, and
second the best conditions to the data collection. We use a step width of
0.02=BA and a step time of 10 s between 20 and 100=BA. Sometimes we smooth
the data to a step width of 0.04 =BA2theta. So, we work with 2500-4000 data
points. Intensities are higher than 20 000 counts. We don't know if these=
=20
experimental sets are alrigth for good statistics. Are they O.K.?=20
If we work at angles lower than 20 =BA2theta the collected intensity=20
increases a lot and it is impossible trying to model the background for=20
the angular region 4-20 =BA2theta. Is there any correction for this?
Thanks in advance
=09=09Paz
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=09
=09Paz Vaqueiro Rodriguez=09=09qfpazvr@uscmail.usc.es
=09Departamento de Quimica Fisica
=09Universidad de Santiago de Compostela