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Abstract:
More than 100 examples are provided of the structural identity
between the cation arrays in oxides and their corresponding
alloys (binary compounds). Halides and halogenates, sulfides
and sulfites and/or sulfates, selenides and selenates,
phosphides and phosphates show this behaviour. In some cases,
the structure of the cation subarray corresponds to the
structure of the alloy at ambient conditions, but in other
cases, cations stabilize structures which correspond to those
of the high-pressure phases of the alloy, from which an analogy
between the insertion of oxygen and the application of pressure
can be established. In this last case, the oxides show
polymorphism with temperature and when heated, the structure of
the ambient pressure of the alloy is recovered as if heating
would compensate the effect of pressure. From the results
reported here, it is concluded that cations do not seem to be
either the isolated entities, predicted by the ionic model,
which occupy interstices of an oxygen matrix, or they arrange
in a more or less arbitrary way, but they try to reproduce the
structure of their corresponding alloy. Many of the phase
transitions and the polymorphism exhibited by the oxides
described here are better explained when they are considered as
formed by previous entities which are the alloys. Oxides should
be considered as 'real stuffed alloys'. These features do not
seem to be casual, but they obey a general principle: Cations
recognize themselves in spite of being embedded in an oxygen
bulk. The nature and the physical meaning of this recognition
are problems which remain unsolved.
