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Fig. 1.8.
The band structure of fcc
α
-Ce, calculated by Skriver.
The orbital angular momentum of some states at symmetry points in the
zone is indicated, including the top and bottom of the narrow bands. The
doubleheaded arrow indicates the spin-orbit splitting of a 4
f
state.
composed of a broad free-electron-like
sp
band, crossed by and hybridiz-
ing both strongly and weakly with the
d
and
f
bands. The occupation
numbers
n
l
of the various states given in Table 1.3 make it clear that
α
-Ce may be classified as both a
d
-andan
f
-band transition metal.
The above description of the
f
states in
α
-Ce as occupying the
bottom of an
f
band is now generally accepted as valid, but the cor-
rect treatment of the
f
electrons in the rare earth metals, and especially
Ce, was a matter of lengthy controversy. According to the standard
model, which is generally applicable to rare earth magnetism, an inte-
gral number of
f
electrons are localized on each ion, subject to the same
intra-ionic interactions as in the free atom. The Pauling-Zachariasen
promotional model for the
γ
-
α
phase transition in Ce, which associ-
ated the transition with the transfer of a single
f
electron on each ion
to a
d
state, with a concomitant decrease of about 6% in the fcc lattice
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