CHEMISTRY
LETTERS,
pp.
537-562,
1975.
Published
THE FORMATION OF HEXAGONAL BaCrO2
.90
Yasuyoshi Government
The
compound
perovskite-like were in This
It is
A and
.90
were
compound
well
transition
structure
a= 5.732
BaCrO2
exist
c=
to
mixed
in
A.
The
by
structures.2,3)
the
oxides
related
the
structure
cubic
The
Japan
of
trial
and
Ba5Ta4O15
parameters of
error
each
atom
method.
type.
several
where
pressure
B is
different
1) and BaMnO3 has 2-, by high
hexagonal
lattice
coordinates
form with
BaCrO3 obtained
to
argon.
a 5-layer
of the BaB4+O3 type,
12-, 14-, and 27-layer modifications.4) closely
of
Nagoya
with
atomic
means
be of
in the hexagonal
hexagonal
Society
462
synthesized
firing
11.920
found
known that
metal,
by
Institute,
Nagoya
was
determined
was
BaNiO3 has a 2-layer gonal
.90
Chemical
WITH A 5-LAYER STACKING SEQUENCE
Research
Kita-ku,
BaCrO2
the
TORII
Industrial
Hirate-machi,
by
a first-row
structures.
4-,
technique
and 9-layer
hexa-
has 4-,
9-,
6-,
These hexagonal layered structures are
perovskite
structure,
and
have
stacking
sequences
of
BaO3layers having completehexagonal close-packing or both hexagonal and cubic close-packing.5) ation
The smaller
of hexagonal
layered
cation
structures.
Ba2CrNbO6 and Ba2CrTaO6 have been two polytypes structure
(6-,
mium oxide obtained
This
feature hexagonal
Cr2O3 (2:1)
This but
at
is
powder well
argon.
in
powder
unit
cell
with
pattern similar
As a result
The
pattern
could
the
that
from of
paper
any
of
be
Ba5Ta4O15.7,8)
the
the
a powdered
completely
a variety This
form-
compounds
cubic
with
perovskite
of the barium-chro-
composition
describes
the
in the
structure
to the
examination
a= 5.732,A, of
study,6)
to transform
of approximate
color
role
the perovskite-like
by firing
dimensions
differs to
with
The present
argon.
an important
previous
of further
phase
of BaCrO2 .90. phase was prepared
1300℃
diffraction
hexagonal
in
In the
prepared
a new hexagonal
by firing
to play
and were found
pressure.
system,
tallographic
X-ray
and 8-layer)
at high
B seems
product
BaCrO2 .90 was preparation and crys-
mixture was
indexed
dark
on
of BaCO3 and brown.
the
basis
c= 11.920
A as
of
polytypes
BaCrO3
new compound
The
shown
also
of
in
a
Table
reported, seems
to
have
1.
558
Chemistry
a 5-layer
close-packing
hexagonal
compound,
does
not
to
ratios
of
powder
pattern
of
peak
5:2
that
of however,
of
and as
and
barium
corresponds
to
Ba5Ta4O15.
3:2
and
1
When two
respectively
new hexagonal
intensities
Table
oxygen
any
other
Observed Intensities
were phase
that
of
fired,
the
were
Calculated the
chemical
formula
oxygen-deficient
of
previously
for
The
mixtures
phases
and
ions.
BaCO3 and
Cr2O3
products
mentioned,
except
observed.
Interplanar Compound
BaCrO2
of
,
The
Spacings .90.
Hexagonal;a= 5.732A, c= 11.920A, V=339.16A3
with gave
the best
and
mole the
low
same values
preparation
and
1975
new
perovskite
reacted
not
Letters
Chemistry of
Letters,
this
ratio
1975
new compound of
2:1.
this
peak
was observed diffraction
this
645℃
The
at
a
of
were
observed to
determine
is
shown
in
Fig.
rate
formation
10℃/min.
of
to this
fired
in
the
mole
hydrogen.
chemical
formula
DTA curve
showed
1.
The
The
weight
gain
of
reaction. and it
the
to have
with
the
chromate
during
estimated
Cr2O3
exothermic
of barium
took place
compound is
when
order
result
sample
BaCO3 and
in
corresponding
in the
new hexagonal
mixture
out
heating
showed the
of Cr ion
result,
carried
the TG curve,
analysis
the oxidation
was
the
products
compound. at
in
from
no reacted
analysis
hexagonal
exothermic
resulted
Then
A thermal of
559
7.44%
The X-ray
supported
heating
that
in air.
the chemical
an
From
composition
of
BaCrO2 .90.
The density of sample measured with a pycnometer was 5.74 g/cm 3, which corresponds to 5 formula weights of BaCrO2 .90 per unit cell (theoretical density, 5.77 g/cm3). The Cr ion in this compound is close to tetravalent state although the solid-state sition
These ability
reaction
metals
phenomena to
often
been
out found
are characteristic
in argon. in alkali
in the
The highly
compounds
i.e.
Na, K, Sr and Ba.
an important
role
to
The cell
dimension
structure,
since
Fig.
stabilize
a high
of BaCrO2 .90 suggests Ba5Ta4O15 has a hexagonal
1
DTA
and
TG
curves
of
oxidizing
and alkaline-earth
form peroxide,
Ba ion plays
like
have
was carried
oxides.
which contain
Hence,
it
oxidation
states
is
the
state
9,10,11)
ions
considered
of tran-
with that
the
of Cr ion.
that this compound has a Ba5Ta4O15 unit cell with a= 5.776 A, c= 11.82
new
hexagonal
compound.
560
Chemistry
A.8)
The structure
oxides
reported
deficient the
of this
to have
compounds.
following
this
the
chemical
b)
the lattice although
not
a common one among oxides.
that
are Ba5Nb4O15, Sr5Ta4O15
The only
and these
1975
other
oxygen
BaCrO2 .90 is
a compound of the Ba5Ta4O15 type,
compounds
not
are raised.
formula
of both
parameter the
is
structure
Assuming
questions
a)
type
Letters,
ionic
is
identical.
of c axis
of BaCrO2 .90 is larger of Cr ion is smaller than that
size
than that of Ba5Ta4O15 of Ta ion.
Ba5Ta4O15 belongs to spacegroup DadP3ml and has a vacant the central
face-sharing
position
Consequently
of which is
the
questions
answered
by the assumption
ion
at
lies
proposed
with
the oxygen
the
atomic those
deficiency
group
in
about
the
as the
reflection
agreement
example
of
each
of
Table
case,
cell
of
from the
of
Fig.
and error
between side
unit
combinations
coordinates
and were
In this
to derive
The trial
100,000
right
coordinates
in the
as in the
Ba5Ta4O13.7)
Good
Cr
to confirm
observed.
BaCrO2 .90 was assumed
atomic
a fifth
for
following
compared
on
be
BaCrO2 .90 were calculated a Facom 270-30 computer on the basis
of the
O(3)
might
of (0,0,1/2)
In order
structure,
intensities with
2.
(0,0,1/2).
that
the position
shown in Fig.
octahedron,
was atom
in
observed 1.
2
Crystal
structure
of
BaCrO2
method carried BaCrO2
and The
out .90
calculated
reliability
for were
eight
atomic
determined
intensities factor
for
parameters. as
was observed
.90.
The
follows:
obtained intensities
as
shown of
Chemistry
the
Letters,
1975
twenty-nine
that
561
peaks
was 0.0982.
Consequently
it
BaCrO2 .90 has a Ba5Ta4015 type structure. As shown in Fig. 2, five chromium ions are
Among them three
fifth
two fifth
of Cr ions
The cross
section
of Cr ions share
form triple
(110)
in octahedral
octahedra
common octahedral
of the hexagonal
corners
plane
is
that
BaCrO2 .90 has a 5-layer hexagonal structure of BaO3 layers. . All of the cations lie in the ing
octahedral
tantalum to
the talum ion seems
.90,
the
size
tend
and
It to
reasonable that
Fig.
of
,90
chromium result
structures;
and (c)
9-layer
that
layered lattice
ion
fifth
the
the
5-layer
structure.
All
in
with of
ions
the
hexagonal
lie
3(a).
oxygens. and
structure. It
of
is
found
ions.
this
in
might
In
the
respect.
This
than
those
compounds
.90 extends
three
6-layer
the
(110)
case
due of
is
because
of
tan-
faces.
Cr It
is a little larger along c direction
hexagonal structure,
plane.
the
differ-
including
sharing
BaCrO2
(b)
be
A structural
octahedra of
Ba5Ta4O15,
This
Ta5+ ions.
cell
layers
in
case
occurs.
type
c axis
structure,
the
smaller
perovskite
of barium-oxygen (a)
six
the perovskite
In
Cr
a little
structures
that
A.
charged
the
are
with
common faces,
shown in Fig.
recognized
parameter
concluding
The repetition
layered
is
sharing
stacking
highly
with
site
as in
Cr-Cr_2.62
the
to conclude
with a stacking sequence a-b-c-b-c (110) plane. The chromium ions shar-
hexagonal
occupied
of the
the
the
Ba5Ta4O15
hexagonal that
with
between
and
charge
Ba5Ta4O15,
3
where
are
supports
have
contact
force
vacancies BaCrO2
ion.
in are
repulsive
between ionic
are
vacancies
high
BaCrO2
than
ion
the
ence
face
seems reasonable
562
Chemistry
for
the
Coulomb
In Fig. encountered These
repulsive
3(b)
and
3(c)
among
the
hexagonal
structures
the
stacking
the
same
are
that
the
sequence
a-b-a-b-c-b-c-a-c.
however,
has
rare
case
type
has In
for
than
a Ba5Ta4O15 case
of is
of
of
Cr ions acting
discussions. for
the
his
and
the
A compound
reported
to
and
is
for
structure.
in
the
have
has
5-layer
is
a stacking
structure,
compounds. composition
It
of
is
larger
in
are
that
of
is
an octahedron in
the his
due
A3,
the
per
chain.
S.
The
reasonable,
gratitude
molecule
respectively,
6-layer
Dr.
Kawahara,
for
in
Japan
and
smaller
average repulsive
these
Ironstone
and
molecule
strong
H. Matsumoto
unit for
cells.
his China
helpful Mfg.
assistance.
J.J.Lander,
Acta Cryst.,
2)
A. Hardy, Acts. Cryst., 15,
3)
Y. Syono and S. Akimoto, J. Phys. Soc. Japan,
4)
B.L. Chamberland,
_h, 148 (1951).
5)
L. Katz and R. Ward, Inorg..Chem., 3,
6)
Y. Torii
7)
F. Galasso and L. Katz,
Acta Cryst.,
14, 647 (1961).
8)
J. Shannon and L. Katz,
Acts. Cryst.,
B26, 102 (1970).
9)
R. Scholder
179 (1962).
Inorg.
26, 993 (1969).
Chem., 8, 286 (1969). 205 (1964).
and H. Matsumoto, J. Ceram. Soc. Japan,
Gushes,
11)
C.C. Addison
and G. Sperka, L. Katz,
in press.
Z. Anorg. Allgem. Chem., 285, 49 (1956).
and R. Ward, J.
and M.G. Barker.
J.
Am. Chem. Soc., 79,
Chem. Soc..
5601
(1957).
5534 (1965).
(Received
February
A3
per
the
the
67.83
6-layer
volume
comparing
octahedra to
is
structure
Because
face-shared
to Mr.
experimental
volume
technique.4)
This
express also
69.75
pressure than
Cr ions to
and
the
1)
B.E.
a
perovskite
References
10)
well
particular,
structure
structure the
are
comparison.
In
9-layer
9-layer
chemical
oxide,
structure.
wishes
the
which
given
perovskite-like
with
62.56
by high is
between
layers
since
hexagonal
are
hexagonal
eighth
octahedra.
structures,
compounds,
structure
BaCrO2.90
including
valuable
third
face-shared
hexagonal
5-layer
barium-chromium
9-layer
Thanks
to.the
the
1975
structure.
structure the
9-layer
in
perovskite-like
in,the
obtained
The auther
Ltd.,
type
structure
5-layer that
number
found
Cr ions
and
5-layer
compound
structures
the
force
been
the
5-layer
9-layer of
that
the
the
not
6-layer
between
of
between
analogous
sequence
as
force
Letters,
24,
1975)
Co.
