Re: "R" mark in the JCPDS-ICDD

Lachlan Cranswick ( lachlan@dmp.csiro.au )
Sun, 12 Nov 95 3:49:23 EST

Forwarded message:
> Reply-To: X-ray X-press <SNYDER@xray.alfred.edu>
>
> The primary use of the PDF is phase ID. If the PDF reference
> pattern lists more lines as being present than a normal resolution
> diffraction pattern would observe, then a user might reject the reference
> as not matching his unknown.

From a user point of view, it would be handy
for phase ID to have ICDD cards for phases
collected under a variety of conditions (diffractometer, film,
flat plate, micro-diffractometer, capilliary, Gandolfi,
calculated, single wavelength, double wavelength, etc).
While a bit off topic, this relates to having both
(Rietveld) calculated data and the raw data as well.

==============

We have had phase ID examples where the ICDD had the patterns
for the raw data - but data calculated from the structure was
more appropriate. Perhaps this could be due to more people using
modern diffractometers with monochromators and sensitive
detectors while many current cards were collected on film or less
sophisticated equipment?

=============

For Rietveld data, having HKL's very close should not be
a problem for most modern search match programs as it
should be visually obvious when peaks are overlapping?
(Though it would be interesting to see what the present
search match algorithms would make of matching a phase
with 3 HKLs very close to each other in the ICDD card
when only one raw data peak is visible?)

==============

Rietveld preferred orientation and other corrections could be
a thorny one. Perhaps a solution is to mention in the card
that preferred orientation was used and on which HKLs?

Cheers,

Lachlan.

PS : I hope this email makes sense. There is a certain time at
night, beyond which it is dangerous to send emails out into the
world. :-)

-- Lachlan M.D. Cranswick          _--_|\  lachlan@dmp.CSIRO.AUCSIRO - Division of Minerals   /CSIRO \ tel +61 3 9647 0367339 Williamstown Rd,           \_.--.*/ fax +61 3 9646 3223Port Melbourne, Australia, 3207      v   (http://www.dmp.csiro.au/tour/lachlan.htm - Still under construction)