I have been using a Seifert powder diffractometer for Rietveld refinement,
with reasonable success (to be published). After having moved away, I still
use this equipment in occasions since resolution and axial divergence are
better than in my actual PW1710.
Although I agree with Lachlan that all diffractometers are approx the same
(depends on your care in alignment and updating), I would like to point out
some key differences:
Our Seifert has two independent axes for th and 2th, which is in any case pre-
ferrable to the fixed th-2th coupling of the old PW1710.
Our seifert has lower axial div than our PW1710, which is fine to avoid
asymmetry for peaks at low th.
Our Seifert has disk-shaped sample holders which can be rotated around psi
to increase the number of crystallites entering Bragg condition (decrease
of graininess). This works, but we observe a slight increase in peak width
(say from 0.090 to 0.095 deg2th) for the rotated sample, and also, the sample
holder makes side loading difficult.
Our Seifert has no automatic div slit, whereas our PW1710 has. Although the
canonical approach uses fixed div slits in order to keep with peak shape
definitions, any such definitions are actually quite blurry and we often
prefer the automatic div slit to get better intensities.
As far as for Siemens D500, it should be very similar to Seifert in per-
formance. One fine goniometer was also the old Rigaku. For Philips Expert,
I have no experience yet.
Hope this helps you
Cheers
Miguel
Prof. Miguel Gregorkiewitz
Dip Scienze della Terra, Universita
Via delle Cerchia 3, I-53100 SIENA, Europe
fon +39'577'298823 fax 298815
email gregor@unisi.it