THE EFFECT OF THE LANTHANIDE
CONTRACTION ON THE
CUBIC
PLATINUM METALS
BY
T. BARTH AN D G. LUNDE
(WITH l TEXTF!G. )
A
t the outset special mention must be made of some ·terms
newly brought out by V. M. GOLDSCHMIDT
1:
The series of elements from cerium to cassiopeium, the
rare earths in a restricted sense, are named the lanthanides.
It has been stated, that within
the
horizontal series
of
the lanthanides, the spacings of the lattice decrease with an in­
creasing atomic number of the metals.
This phenomenon is
named the lant h anid e contraction.
We cannot in this paper discuss the great importance of
the lanthanide contraction, but may only refer to the said papers
of V. M. GOLDSCHMIDT and
co-workers.
An obvious conse­
quence of the contraction becomes, however. conceivable by the
following considerations:
Within a vertical column of the periodic system the spacings
of the atomic lattice increase with an increasing atomic number.
But when two
elements belonging to the same vertical
colurnn of the periodic system are separated by the lanthanides,
the
said increase of the dimensions of the space lattice is
more or less compensated by the lanthanide contraction.
compensation
will
consequently
be most
salient in
This
the ele­
ments zirconium-hafnium and those imidiately following, i. e.,
l
Geochemische Verteilungsgesetze der Elemente IV und V:
lY:
V. M. GoLDSCHM.IDT,
F. ULRICH und T. BAr<TH:
Zur Krystall­
struktor der Oxyde der seltenen Erdmetalle.
V:
V. M. GOLDSCHMIDT, T. BAHTH und G. LUNDE:
Polymorphie der Sesquioxyde.
ihre Konsequenzen. Vid. Akad. Skr
No. 5 and No. 7.
lsomorphie und
Die Lanthanide -- Kontraktion und
I. Mat.-Nat. Kl. (Oslo) 1925
THE LANTHANIDE CONTRACTION
221
two homologous elements, located within this area of the peri­
odic system, as e. g. palladium-platinum, will not show the normal
relative increase of the space lattice. 1
The older spacing measurements of such homologous ele­
ments which might give a conception of the quantity of the
contraction are often inconsistent and little exact.
The object, therefore, of our investigations was to collect
results showing the general
effect or the lanthanide con­
traction on the succeeding
.
A
elements ellucidated by accu­
rate measurements.
At the proposal of Pro­
d
fessor V. M. GoLDSCHMIDT
we undertook
the investi­
gation of the cubic platinum
metals,
as
these
elements
in our opinion represent the
o
A
J.s
most convenient group.
Powder
photographs
have been made and struc­
tures assigned to all of the
·
metals of this group, as well
f------J, 7
.36
- ---
f----- -
7
x(b
-----
/RI)
--
�·
3 J f----- - -- -
as determinations of a0 the
length of the edge of the
unit cube.
/
(--
P.r
/Ypd
'0-
Fig. l.
One of these determinations has been carried out
with great accuracy by R. W. G. WYCKOFF2 and according to
a new method brought out by the said author.
He made a
comparison measurement by mixing the sample directly with
sodium chloride to serve as a standard.
Using the principle of WYCKOFF's method we have made
accurate measurements on rhodium, palladium and platinum,
l
It should be mentioned that G. de HEVES Y new ly has observed this
phenomenon in the case of zirconium-hafnium: "Recherches sur la
proprietetes du Hafnium''.
(Copenhagen) Yl, 7. 1 925_
2 z_ Kr. 59, 55
(HJ23).
Det Kgl. Danske Vid. Selsk. Math. fys. Medd .
.
T. BARTH AND
G. LUNDE
222
besides determinations on ordinary powder photographs of these
three metals and of iridium.
The results of the determinations yield:
=
3 795
3 8 23 t
cm. 10-s
ao
=
3 . 873
a0
�
3 903
cm. l o-8
a0
For rhodium
iridium
a0
"
palladium
"
platinum
=
cm. l o-8
·
·
cm. 10-8
·
The graphic table of fig. l gives a good image of the effect
of the lanthanide contraction on the two heaviest metals, iridium
and platinum.
It has been assumed that the platinum metals have a face­
WYCKOFF2 has discussed the possibil­
centered space lattice.
ities of the different atomic arrangements as regards iridium.
He states that it has the said lattice; the unit cube containing
four atoms in the following positions:
000; HO; OH; !O�;
But the intensities of the three other metals, observed by
A. W. HuLL, 3 have been in disagreement whit this atomic arrange­
ment4.
According to our investigations, however, all four metals
Table
I.
lnt e ns i ty
l
I ron-target
lndices
C ale.
Pd.
(Ill)
lO
(2001
(220)
(311)
5
5
(222)
( 400)
(331)
l
l
Calc.
Pd.
Rh. Pt. I r.
3
9
6
6
8
3
-
� ---
--·-
-
lO
l
l
Copper target
Obs.
l
l
lO
5
5
l
I
l
7
2
l
7
Ob.served
Rh.
6
5
5
4
2
l
5
l
l
Pt.
8
5
5
8
2
l
3
l
l
·-
Ir.
lO
9
9
lO
5
3
5
t According to WYCKOFF, loe. cit., as well as our own measurements
which a gree well with his data.
2
loe. cit.
3
A. W. HULL:
4
Rev. 17, 571 (1921).
Cfr. R. W. G. WYCKOfF:
254- 256.
X-Ray Crystal Analysis of thirteen common Metals. Phys.
"The Strukture
of Crystals".
N. Y. 1924 p.
THE LANTHANIDE CONTRACTION
223
show a good agreement with the said atomic arrangement, as
seen by table I.
We have thus stated that all four metals have the same
atomic arrangement; and all data lead to the conclusion that the
only possible arrangement is that which WYCKOFF has stated
for iridum.
We shall not in this paper discuss the experimental methods
nor the measurements and calculations of the films.
All the
experimental data are published in detail by us in "Zeitschrift flir
physikalische Chemie"
l 925.
Mineralogical Institute of the University.
Oslo, june 27th, 1925.