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RE: contribution to working group

• To: Multiple recipients of list <phase-identifiers@iucr.org>
• Subject: RE: contribution to working group
• From: "S. C. Abrahams" <sca@mind.net>
• Date: Tue, 9 Apr 2002 20:00:51 +0100 (BST)

Dear David and fellow members:

Thoughts inspired by Jean-Claude's message this morning:

7.1.  I agree with him that, at least for inorganic compounds (including
intermetallics), composition should be an essential part of any internal
identifier if pertinent information residing in all types of databases is
thereby to be accessible.

Regarding solid solutions, since they necessarily involve a range of
composition,
with properties that may be dependent on a very narrow range, the inclusion
of a
numerical indication is probably obligatory. For example, piezoelectric PZT
(as
widely used industrially) may be represented as Pb[Zr(1-x)Ti(x)]O3 with
electromechanical properties of maximum value in the range x ~ 0.5 to 0.6. A
given paper may well refer to a highly specific value of x in this range,
hence
the identifier must be able to retrieve that paper as well as others with
nearby
composition. A possible problem that an external identifier will have to
avoid
is in being either too broad or too narrow in retrieving a given mixed
composition.

7.2   It would be more user-friendly if we could devise an approach in which
either an internal or external identifer were acceptable.

7.3   I prefer to leave this question for comment by those members who are
more
database knowledgeable.

7.4   Jean-Claude has identified a problem of considerable importance. There
are clear advantages in formulating identifiers that are universally
applicable
to all kinds of crystalline phases, and I would hope we can achieve such a
phase
identifier(s).

7.5   If a hybrid system proves possible, and in principle there seems to be
no
reason why not, that might eliminate many problems for us.

7.6   I look forward to proposals by others more expert than I in this
field!

Best wishes.

Sidney
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Prof. S. C. Abrahams
Physics Department
Southern Oregon University
Ashland, OR 97520

Fax: (541) 552-6415   Tel: (541) 482 7942
Email: sca@mind.net
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