> I need to know which are the oldes references regarding the BaTiO3
> crystallography and phase transformation.
According to ICSD the oldest reference is:
Goldschmidt, V.M. "Geochemische Verteilungsgesetze VIII. Bau und
Eigenschaften von Krystallen "(1927) Skrifter utgitt av det Norske
Videnskaps-Akademi i Oslo 1: Matematisk-Naturvidenskapelig Klasse 1927,
1-156
As Simon said :-) the material was of great interest during WW2 for its
ferro-electric properties:
von Hippel et al. (1946). Ind. Eng. Chem. 38, 1089.
Internationale Tabellen zur Bestimmung yon Kristallstructuren
(1935), Vol. 2. Berlin: Gebriider Borntraeger.
Helen Megaw published her WW2 work on this in 1945. However the actual
atomic displacements responsible for ferro-electricity in the room
temperature tetragonal structure remained unknown, and a measurement was
only attempted after the growth of a small single crystal by Evans (1951):
Evans, H.T.Jr. The crystal structure of tetragonal barium titanate
(1951) Acta Crystallographica 4, 377-377
Yet ten years later, Evans was to conclude (1961)
"it became apparent that the structure is essentially indeterminate".
Evans, H.T.Jr. An X-ray diffraction study of tetragonal barium titanate
(1961) Acta Crystallographica 14, 1019-1026
Helen Megaw in (1962) was not quite so pessimistic:
Megaw, H.D. Refinement of the structure of Ba Ti O3 and other ferroelectrics
(1962) Acta Crystallographica 15, 972-973
But there remained a fundamental problem in quantitatively relating the
measured electrical polarisation of the bulk material to the displacements
of charged atoms from high symmetry positions. This was due to the
difficulty of obtaining single crystals, extinction effects caused by
large strains in the crystals that were available, electrical charge
accumulating on grain boundaries, problems in refining pseudo-symmetric
structures, problems with refining light atom positions with X-rays in the
presence of heavy atoms etc...
These problems were really only overcome with the development of
Rietveld's method for neutron powder diffraction where such systematic
errors were largely avoided.
I suppose that today the structure of ferro-electric BaTiO3 at room
temperature must seem trivial - something that must surely have been clear
in the 1940's - but if you are interested in the history, and want to
understand how difficult it really was until much later, you can do no
better than to read some of these early papers.
Alan.
_____________________________________________________________
Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48
+33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/
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