vacant. Therefore, we studied the possibility of occupying the cation
vacancies in the alumina surface by the Pt ions. In this case, the
d-RDF should exhibit the strong Pt–Pt contributions reflecting dis-
tances between the Pt ions located in the O h sites (B–B distances).
The Pt–O (B–O distances) and Pt–Al (B–B, A–B distances) con-
tributions arising from bonding with the alumina atoms are also
expected.
The nanocrystalline ?-Al 2 O 3 oxides expose predominantly
(1 1 0) faces [35]. Recently, it was shown that interaction regions
exist as remote islands rather than as a continuous layer [11,42].
We considered models with random distribution of the Pt ions over
the vacant O h sites within regions 1 × 1 × 0.5 nm in size on the (110)
alumina face. Model 1 and model 2 assumed filling 100% and 30% of
the vacancies, respectively. Fig. 5 shows the experimental d-RDF in
comparison with the calculated RDFs. The peak positions match
very well. The calculated RDF for model 2 is characterized by a
reduction of the Pt-Pt contributions due to decrease in a probability
of Pt–Pt bonds. A better agreement between the experimental and
model RDFs is provided with the assumption of partial occupation
of the vacancies.
Some discrepancies are nevertheless observed. The experimen-
tal d-RDF features a stronger coordination peak at 3.4 ˚ A. This
distance is characteristic of the atomic ordering around cations in
the T d sites of the alumina structure (A–A, A–B distances). There-
fore, the model assuming an insertion of the Pt ions into the vacant
tetrahedral sites along with the octahedral ones on the alumina
surface was also considered. According to model 3, the Pt cations
occupy 30% of the vacant O h and T d sites at the 4:1 ratio.