Abstract
The R2PdSi3 intermetallic compounds have been reported to crystallize in a hexagonal AlB2-
derived structure, with the rare earth atoms on the Al sites and Pd and Si atoms randomly distributed
on the B sites. However, the intricate magnetic properties observed in the series of compounds
have always suggested complications to the assumed structure. To clarify the situation, x-ray
and neutron diffraction measurements were performed on the heavy rare earth compounds with R
= Gd, Tb, Dy, Ho, Er, Tm, which revealed the existence of a crystallographic superstructure. The
superstructure features a doubled unit cell in the hexagonal basal plane and an octuplication along
the perpendicular c direction with respect to the primitive cell. No structural transition was observed
between 300 K and 1.5 K. Extended x-ray absorption fine structure (EXAFS) analysis as well
as density functional theory (DFT) calculations were utilized to investigate the local environments
of the respective atoms. In this article the various experimental results will be presented and it will
be shown that the superstructure is mainly due to the Pd-Si order on the B sites. A structure model
will be proposed to fully describe the superstructure of Pd-Si order in R2PdSi3. The connection
between the crystallographic superstructure and the magnetic properties will be discussed in the
framework of the presented model.
