Synthesis and Crystal Chemistry of a New Manganite Member Bi3.6Sr12.4Mn8O28+δ,n=2 of the [Bi2Sr2MnO6]n[Sr8Mn 6O16+δ]-Related Tubular Family

Article abstract of DOI:10.1006/jssc.1998.7784

A manganite with a tubular structure derived from the 2201-type, Bi_3.6Sr_12.4Mn₈O_28+δ, has been synthesized. Its complex crystal chemistry has been studied using XRD, ND, and HREM techniques. It crystallizes in an orthorhombic cell, space groupPbnb, witha=5.4946 A,b=23.595(1) A, andc=23.580(1) A. This structure can be described as an intergrowth, along b, of two types of (010) slices: 2201 -type slices [Bi₂Sr₂MnO₆] that are two octahedra thick and manganese-deficient perovskite-related slices [Sr₈Mn₆O_16+δ] that are one octahedron thick. A similar stacking is observed along c, which endows the structure with a pseudotetragonal character. Another way to describe this structure is to consider criss-crossing layers of manganese polyhedra forming tubes, where the [BiO] rows are inserted, and oxygen-deficient pillars, built up of four Mn polyhedra. This phase represents then=2 member of a new tubular family [Bi₂Sr₂MnO₆]_n[Sr₈Mn ₆O_16+δ]. Intergrowth and shearing mechanisms arise along the b and c directions, in agreement with the pseudotetragonal character of the structure. The investigation of the transport and magnetic properties of this new manganite shows that it is an insulator and exhibits weak antiferromagnetism at low temperature (θp=-650 K); the high-temperature data evidence an effective magnetic moment of 4.7μ_Bcharacteristic of high-spin Mn³⁺(μ_th=4.9μ_B).

Full text of DOI:10.1006/jssc.1998.7784

JOURNAL OF SOLID STATE CHEMISTRY 138, 278—289 (1998)
ARTICLE NO. SC987784
Synthesis and Crystal Chemistry of a New Manganite Member
Bi3.6Sr12.4Mn8O28؉d, n ؍ 2 of the [Bi2Sr2MnO6]n[Sr8Mn6O16؉d]-Related
‘‘Tubular’’ Family
D. Pelloquin, C. Michel, A. Maignan, M. Hervieu, and B. Raveau
Laboratoire de Cristallographie et Sciences des Materiaux, ISMRA-Universite de Caen, Boulevard du marechal Juin, 14050 Caen Cedex, France
Received October 1, 1997; in revised form February 3, 1998; accepted February 5, 1998
obtains layered structures, intergrowths of perovskite and
rock salt-type layers. This is the case of the bismuth cuprates
and manganites, which only differ by the oxygen stoichiometry
A manganite with a ‘‘tubular’’ structure derived from the
2201-type, Bi3.6Sr12.4Mn8O28؉d, has been synthesized. Its com-
plex crystal chemistry has been studied using XRD, ND, and of their perovskite layers, leading to the formulas
HREM techniques. It crystallizes in an orthorhombic cell, space
group Pbnb, with a ؍ 5.4946 A, b ؍ 23.595(1) A, and c ؍
23.580(1) A. This structure can be described as an intergrowth,
along b, of two types of (010) slices: ‘‘2201’’-type slices
[Bi2Sr2MnO6] that are two octahedra thick and manganese-
deficient perovskite-related slices [Sr8Mn6O16؉d] that are one
octahedron thick. A similar stacking is observed along c, which
endows the structure with a pseudotetragonal character. Another
way to describe this structure is to consider criss-crossing layers
of manganese polyhedra forming tubes, where the [BiO] rows
are inserted, and oxygen-deficient pillars, built up of four Mn
Bi Sr Ca
Cu O
(7, 19) respectively.
(3—6) and Bi (Sr, Ca)
Mn
ꢀ
ꢀ
K\ꢁ K ꢀK>ꢂ>B
ꢀ
K>ꢁ
K
O
ꢃK>ꢃ>B
In the case of copper-based oxides, the formation of
transverse slices, perpendicular to the copper layers, allows
new compounds to be generated. These new compounds
derive from the layered cuprates either by single or double
shearing mechanisms forming the ‘‘collapsed’’ cuprates
(8—10), or by more complex phenomena forming the ‘‘tubu-
lar’’ cuprates (11—13). In contrast, no collapsed- or tubular-
type structure has been evidenced to date for manganites, in
polyhedra. This phase represents the n ؍ 2 member of a new spite of the great analogy between the layered cuprates and
‘‘tubular’’ family [Bi2Sr2MnO6]n[Sr8Mn6O16؉d]. Intergrowth
and shearing mechanisms arise along the b and c directions, in
agreement with the pseudotetragonal character of the structure.
The investigation of the transport and magnetic properties of this
new manganite shows that it is an insulator and exhibits weak
antiferromagnetism at low temperature (hp ؍ ؊650 K); the
high-temperature data evidence an effective magnetic moment
of 4.7 lB characteristic of high-spin Mn3؉ (lth ؍ 4.9 lB). ( 1998
Academic Press
manganites. This issue is of great interest for the study of the
magnetic and transport properties of the manganese oxides.
We have thus investigated the formation of such com-
pounds in the system Bi—Sr—Mn—O. We report herein on the
first manganite, Bi Sr
bular’’ structure. The complex crystal chemistry of this
phase, which represents the only known n"2 member of
the ‘‘tubular’’ series [Bi Sr MO ] [Sr M O
Mn O
, that exhibits a ‘‘tu-
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ ꢀꢆ>B
] (M"
ꢀ
ꢀ
ꢅ L
ꢆ
ꢅ ꢁꢅ>B
Cu, Mn), is described from high resolution electron micros-
copy and neutron diffraction data.
INTRODUCTION
The discoveries of superconductivity at high temperature
in copper-based oxides more than 10 years ago (1), and
more recently colossal magnetoresistance (CMR) properties
EXPERIMENTAL PROCEDURE
The Bi—Sr—Mn—O system was investigated close to the
in manganese-based oxides (2), have demonstrated that ideal composition expected for an n"2 member of the
transition metal oxides represent a very promising source tubular-type oxides (13), that is, Bi Sr Mn O
. Two
ꢂ
ꢁꢀ
ꢆ ꢀꢆ>B
for new materials with optimized properties. Curiously types of starting mixtures were considered to prepare sam-
these two classes of compounds exhibit a great similarity in ples with the above nominal composition. A first method
spite of their fundamentally different physical properties. was to start from a mixture of Bi O , SrO , and
ꢀ ꢃ
ꢀ
They both derive from the perovskite-type structure in Mn/Mn O in various ratios in order to control the oxygen
ꢀ ꢃ
which the transition element is characterized by a Jahn content. The precursors were weighted according to the
Teller effect and shows a mixed-valence Cu(II)—Cu(III) chosen cationic composition, intimately ground in an agate
or Mn(III)—Mn(IV). Consequently in the two systems, one mortar, and placed in an alumina finger. Next, the mixtures
278
0022-4596/98 $25.00
Copyright ( 1998 by Academic Press
All rights of reproduction in any form reserved.

NEW MANGANITES Bi Sr
Mn O
279
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
were sealed in an evacuated silica ampoule. Unfortunately,
in this method, impurities like Bi Sr MnO
and
ꢀ\V ꢀ\W
ꢅ>B
Sr Mn (CO )O were systematically detected. A second
ꢇ
ꢂ
ꢃ
ꢁꢈ
method was to start from mixtures of Bi O , SrO, and
ꢀ ꢃ
Mn O . To avoid the carbonate contamination, SrO was
ꢀ ꢃ
initially prepared by decomposing SrO or Sr(OH) , 8H O
ꢀ
ꢀ
ꢀ
at 1100°C, and stored in a dry box. This step was performed
in a dry box. Then the compounds were heated to 1050°C, at
150° h\ꢁ, kept at this temperature for 24 h, and cooled to
room temperature, at 150°C h\ꢁ.
The electron diffraction (ED) study was carried out using
a JEOL 200CX electron microscope fitted with an eucentric
goniometer ($60°). The high resolution electron microscopy
(HREM) was performed with a TOPCON 002B operating at
200 KV (point resolution of 1.8 A). HREM image calculations
were carried out with the Mac-Tempas multislice program.
The two microscopes were equipped with EDX analyzers.
The initial structural model was refined first from powder
X-ray diffraction (XRD) data, collected with a Philips verti-
cal diffractometer (CuKa radiation) in the range 6°42h4
110° by increments of 0.02° (2h), and next from neutron
diffraction (ND) data. The latter were collected at room
temperature on D2B diffractometer (j"1.5938 A) at the
Institut Laue Langevin (Grenoble, France) over the angular
range 0°(2h(140° with a step of 0.05° (2h). The scatter-
ing lengths were 0.8532, 0.7020, 0.373, and 0.5803 (in
10\ꢁꢀ cm) for Bi, Sr, Mn, and O, respectively. All structural
calculations were performed by profile analysis with the
program Fullprof (version 3.2) (14).
RESULTS
Under the synthesis conditions mentioned above, a new
phase in the Bi—Sr—Mn—O system was obtained. Pure sam-
ples were only obtained for d close to 2, i.e., a nominal
oxygen stoichiometry of 30 oxygens per formula unit.
Cell Parameters and Homogeneity Range
The reciprocal space for numerous crystallites was recon-
structed, by tilting about the crystallographic axes. EDX
analyses were systematically coupled. These first analyses
showed that the new material exhibits an orthorhombic cell
with a+a (2+5.5 A (a is the parameter of the cubic
ꢀ
ꢀ
perovskite-type structure) and b+c+23.6 A+c
ꢀꢀꢈꢁ
being the periodicity of the layer stacking in the
(c
ꢀꢀꢈꢁ
2201-type structures). The conditions limiting the reflections
are hkl : h#k, k#1, l#h"2n, compatible with the space
groups Fmmm and Fmm2. The superstructure reflections are
rather intense and lie in commensurate positions, contrary
to what is observed in the 2201-compound, Bi Sr MnO
(7), which exhibits an incommensurate modulated structure
with a periodicity b"q.a (2 (q+4.9). The [100] and intense reflections characteristic of the F-type lattice, a sec-
[010] ED patterns are given in Fig. 1.
FIG. 1. (a) [010] and (b) [100] ED patterns. Extra reflections violating
the F-type conditions are indicated by small white arrows on the experi-
mental and schematic [100] patterns.
ꢀ
ꢀ
ꢅ>B
However, in most of the crystallites, in addition to the
ꢀ
ond system of very weak reflections is observed, which

280
PELLOQUIN ET AL.
implies that the F-type conditions are violated. These weak the zones of high electron density are imaged as bright dots.
reflections obey only the conditions 0kl : k"2n, hk0 : k"2n The contrast consists in a regular paving of 4;4 bright dots
and h0l, h#l"2n, compatible with the space group Pbnb. squares, separated by perpendicular criss-crossing rows of
They are indicated by small white arrows in Figs. 1a and 1b. gray dots. Referring to the HREM images recorded for the
Their relative arrangement gives evidence for the existence 2201-type compounds (18) and the ‘‘tubular’’ phases (12, 13),
of twinning domains, as the [010] and [001] variants are the intense bright dots are correlated to the positions of Bi
systematically superposed; this is clearly seen in Fig. 1b.
and Sr atoms and the gray ones to the manganese positions.
The EDX analyses show that the Sr/Bi ratio is slightly The great similarity of these images to those previously
higher than the theoretical value, i.e., 3.4 instead of 3, lead- observed for the ‘‘tubular’’ cuprates (12, 13) allows a first
ing to the actual composition Bi Sr
diffraction pattern is given in Fig. 2. The refinement of cell
Mn O . The XRD approach to a structural model to be proposed.
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ V
In this model (Fig. 3b), the structure consists in the
parameters in the space group Pbnb led to a"5.4946(1) A, intergrowth, along b, of two types of (010) slices. The first
b"23.595(1) A, and c"23.580(1) A. Note that the c para- slice exhibits the 2201-type structure, Bi Sr MnO
, and is
ꢀ
ꢀ
ꢅ>B
meter is very close to that previously refined for the Mn- two Mn octahedra wide. The second is a perovskite-related
based 2201-type compound (7).
slice, [Sr Mn O
]. In that way, this new structure is
ꢆ
ꢅ ꢁꢅ>B
For the characterization of this new structure, we have characteristic of the ‘‘tubular-2’’ structure. Referring to the
first considered the average structure, i.e., the F-type lattice. general formulation proposed for members of the ‘‘tubular’’
In a second step, we have taken into consideration the family (13), its ideal composition would be [Bi Sr Mn
neutron diffraction data and the actual P-type lattice in
order to understand the origin of the symmetry lowering close to the actual cationic composition, Bi Sr
and to clarify the oxygen positions in the pillars. Finally, obtained by EDX. The spectacular characteristic of this
local features and defects are discussed in order to under- n"2 member of the ‘‘tubular’’ family is that the layer
stand the structural mechanisms that govern the structure. stacking sequence, that is, the 2201-type mode, is formed
along two perpendicular directions, b and c. Note that this
ꢀ
ꢀ
O
$ ] [Sr Mn O $ ], i.e., Bi Sr Mn O
, which is
Mn ,
ꢅ B ꢀ
ꢆ
ꢅ ꢁꢅ B ꢁꢀ
ꢂ
ꢆ ꢀꢆ$B
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
framework and these cell parameters were predicted pre-
viously (13), but the compound was never stabilized in the
The Average Structure
The origin of the superstructure along b was studied Bi—Sr—Cu—O system.
by high resolution electron microscopy, selecting [100]
A first set of positional parameters in the Fmmm space
oriented crystals. A typical image is given in Fig. 3a, where group was calculated from the ideal model deduced from
FIG. 2. Powder X-ray diffraction pattern limited to 2h460° registered with CuKa radiation (j"1.5418 A). The indexes refer to Pbnb space group.

NEW MANGANITES Bi Sr
Mn O
281
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
FIG. 3. (a) [100] HREM image. In some places, the elongated, cross-shaped contrast observed at the level of the pillar is indicated by black triangles;
(b) projection of the idealized model of the ‘‘tubular-2’’ structure; (c) projected potential (PP 2;2 cells), and comparison between the images calculated for
the F-type and P-type models (the focus values are !45 and !50 nm respectively).
the HREM study and refined from neutron data. Conver-
Thanks to the structural particularities of the ‘‘tubular-2’’
gence was obtained for the refined values listed in Table 1, structure, two ways to describe the location of the manga-
leading to a Bragg R factor R "0.078. These results con- nese atoms exist. The first is to consider that the manganese
firm the proposed model for this new structure, i.e., a ‘‘tubu- atoms are located in two types of atomic rows: one is
lar-2’’ structure, and the slight bismuth deficiency, with parallel to b and belongs to the 2201 slice; whereas the
regard to the theoretical value, deduced from EDX analysis. second is parallel to c and belongs to the perovskite-related

282
PELLOQUIN ET AL.
occupies one of the four positions generated by the space
TABLE 1
group. This situation is different from that observed for the
copper-based ‘‘tubular-4’’ structure and involves Mn—O
polyhedra different than the Cu—O ones for the atoms
forming the ‘‘cycle.’’ Seeking additional information about
the pillar, particular attention was paid to the HREM
images. The theoretical HREM images, calculated from the
refined positional parameters given in Table 1, showed that
two of the characteristic contrasts of the ‘‘pillar’’ are one
very bright spot (correlated to a light electron density zone)
and a cross-shaped bright dot. In every case, whatever the
focus value, a fourfold symmetry is calculated for the posi-
tional parameters of the average structure (F-type lattice).
Refined Variable Parameters in the Space Group Fmmm
(Estimated Standard Deviations Refer to the Last Digit)
Atom
Site
x
y
z
B (Aꢀ)
n
Bi
16m
8h
8h
8i
8i
16m
16m
16m
32p
16o
16o
16n
8d
0
0
0
0
0
0
0
0
0.3133(3) 0.1906(4) 0.3(1)
14.2(2)
8
8
8
8
16
16
16
15.0(3)
16
8
Mn1
Mn2
Mn3
Mn4
Sr1
Sr2
Sr3
O1
0.0886(9)
0.307(1)
0
0
0.8(2)
0.8(2)
0
0
0.0702(9) 0.8(2)
0.301(1) 0.8(2)
0.1984(4) 0.0758(4) 1.04(6)
0.0808(5) 0.4182(4) 1.04(6)
0.0807(5) 0.1921(4) 1.04(6)
0.1806(7) 0.1906(5) 0.83(6)
0.119(1)
0.257(2)
0.220(4)
0.284(2)
0.25
O2
O3
O4
O5
O6
O7
O8
O9
0.1366(6)
0.253(2)
0
0
0.83(6)
0.83(6)
An example is given in Fig. 3c (labeled F ) for focus values
—
of !45 and !50 nm, which are assumed to be close to the
experimental values in Fig. 3a. In fact, a contrast anomaly in
the thin edges of the crystallites is detected at this level. For
a few focus values, the contrast is not symmetrical but
consists in one elongated dot, extended along one of the
pillar diagonals (see for example the black triangles in
Fig. 3a). The orientation of these elongated dots varies from
one pillar to the adjacent ones, so that artifact effects such as
small crystal or beam tilting, which were shown to be crucial
for tunnel structures, can be discarded. This suggests that, in
the oxygen rows running along a within the pillars, the
distribution of the oxygen atoms is not really statistical over
the four positions generated by the F-type lattice. The space
0
0
0.1336(5) 0.83(6)
0.25 0.83(6)
16
8
16m !0.037(2)
0.3118(5) 0.0973(6) 0.83(6)
0.0826(4) 0.0732(6) 0.83(6)
0.1040(5) 0.3012(5) 0.83(6)
16
16
16
8.0(3)
16m
16m
32p
0
0
0.25
0.0271(8) 0.014(1)
0.83(6)
Space group
Cell parameters
a"5.4945(1) A
b"23.594(1) A
c"23.581(1) A
R factors
R "0.047
ꢀ
Fmmm (n°69)
R
"0.062
ꢁꢀ
R "0.076
slice. The second way is to consider that the manganese group Pbnb, determined by considering the weak extra
atoms belong to equivalent but perpendicular ‘‘octahedral’’ reflections in the ED patterns, allows the initial (32p) site of
layers of the 2201 structure. Both are sandwiched between the oxygen O(9) to be divided into independent (8e) crystal-
two [SrO] rows, and the crossing of the two manganese lographic sites.
rows forms ‘‘pillars’ characterized by the existence of square
Mn ‘‘cycles’’ of four edge-sharing manganese polyhedra
(the four Mn atoms are located at the same x). In the
ꢂ
Actual Structure
tubular-4 cuprate, the ‘‘pillars’’ were shown to be only
Working in the Pbnb space group implies an increase in
partially occupied by oxygen atoms (12), so that the copper the number of independent atoms relative to the Fmmm
atoms belonging to the cycle form either CuO bipyramids space group. Positional parameters issued from the average
ꢇ
(for the occupied oxygen position in the pillar) or CuO
structure (Table 1) were calculated to be compatible with
ꢂ
tetrahedra (for the vacant position). But a higher occupancy Pbnb and used as starting parameters. Particular attention
of these oxygen sites is possible and has to be taken into was paid to the oxygen atoms located inside the pillar.
consideration, especially in the case of manganese, which Considering an oxygen-free pillar, the Fourier difference
tends to form MnO octahedra. The neutron diffraction map section calculated at x"0.25 clearly showed two resi-
ꢅ
study confirms this viewpoint. It shows the presence of extra dues approximately symmetrical with regard to the origin,
oxygen, labeled O(9) in Table 1, inside the pillar so that the with coordinates y+z+0.015 (Fig. 4). Two sets of oxygen
ideal formula of the perovskite slice is no longer labeled O(16) and Oꢀ(16) and located in the (8e) crystallo-
[Sr Mn O ] but rather [Sr Mn O
oxygen content (eight per unit cell) is higher than that calculations. Refinements of positional parameters, bismuth
observed in the copper-based ‘‘tubular-4’’ compound (4.3 occupancy, and isotropic B factors for each kind of atoms
] . The refined graphic site with half occupancy were then introduced in the
ꢆ
ꢅ ꢁꢅ ꢉ
ꢆ
ꢅ ꢁꢅ>B ꢉ
per unit cell (12)). These oxygen atoms are randomly distrib- allowed the following R factors to be obtained: R "0.039,
ꢀ
uted over the positions of the (32p) crystallographic site R "0.051, and R "0.063. Note that these values are
ꢁꢀ
(x, y, z with x"0.25, y"0.011, and z"0.028), but this significantly lower than those obtained using the Fmmm
implies that two oxygens are present in a pillar, one at space group (Table 1). Finally, occupancies of all oxygen
x"0.25 and the second at x"0.75, to avoid oxygen—oxy- sites were refined, leading to a decrease of R factors:
gen distances that are too short. For a given x value, oxygen R "0.037, R "0.048, and R "0.057. Note that it was
ꢀ
ꢁꢀ

NEW MANGANITES Bi Sr
Mn O
283
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
TABLE 2
Refined Variable Parameters in the Pbnb Space Group
(Estimated Standard Deviations Refer to the Last Digit)
Atom Site
x
y
z
B(Aꢀ)
n
Bi(1)
Bi(2)
Mn(1) 8e
Mn(2) 8e
Mn(3) 8e
Mn(4) 8e
Sr(1)
Sr(2)
Sr(3)
Sr(4)
Sr(5)
Sr(6)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
8e
8e
0
0
0
0
0
0
0
0
0
0
0
0
0.3081(7)
0.6866(8)
0.0866(9)
0.3101(9)
0
0.1910(7) 0.4(1)?
0.1879(9) 0.4(1)?
8D
6.1(1)
8D
0
0
0.8(1)@
0.8(1)@
8D
0.0747(9) 0.8(1)@
0.3038(9) 0.8(1)@
0.0762(9) 0.7(3)A
0.0754(8) 0.7(3)A
0.4149(8) 0.7(3)A
0.4180(9) 0.7(3)A
0.1909(6) 0.7(3)A
0.1909(8) 0.7(3)A
8D
0
8D
8e
8e
8e
8e
8e
8e
8e
8e
8e
8e
8e
8e
8e
4d
4c
0.1976(7)
0.8005(7)
0.0844(7)
0.9282(7)
0.0854(7)
0.9237(6)
0.182(1)
0.816(1)
0.132(1)
0.139(1)
0.249(1)
0
8D
8D
8D
8D
8D
FIG. 4. Fourier difference map section at x"0.25 calculated in the
space group Pbnb and showing the two residues attributed to the oxygens
(O(16) and Oꢀ(16)) located inside the pillar.
8D
0.124(3)
0.091(3)
0.283(5)
0.740(4)
0.219(3)
0.271(4)
0.722(4)
0.75
0.192(1)
0.176(1)
0
0
0
0.136(1)
0.135(1)
0.25
1.02(5)B 8D
1.02(5)B 7.2(4)
1.02(5)B 8D
1.02(5)B 8D
1.02(5)B 7.2(2)
1.02(5)B 8D
1.02(5)B 8D
1.02(5)B 4D
1.02(5)B 4D
not possible to show any difference between the occupancy
of O(16) and Oꢀ(16) sites. The refined values are listed in
Table 2 and the corresponding calculated diffraction pat-
tern is drawn in Fig. 5. Based on the R values, the results can
be considered to be representative of the structure.
As indicated above, the use of Pbnb space group increases
the number of independent atoms compared to the F-type
space groups. Most of them, except manganese and some
oxygen atoms, are multiplied by a factor of two. Constraints
on the coordinates would permit a pseudo-F lattice: for
0
0
0
0.25
0.25
O(10)
O(11)
O(12)
O(13)
O(14)
O(15)
O(16)
8e !0.012(5)
8e
8e
8e !0.012(5)
8e
8e
8e
0.3084(9)
0.6963(8)
0.0898(7)
0.9238(7)
0.1087(8)
0.8959(9)
0.0248(7)C
0.0948(8) 1.02(5)B 8D
0.0943(9) 1.02(5)B 8D
0.0816(8) 1.02(5)B 7.3(2)
0.0728(8) 1.02(5)B 8D
0.3047(9) 1.02(5)B 8D
0.3108(8) 1.02(5)B 5.9(3)
0.0130(9)C 1.02(5)B 4D
0
0
0
0.029(5)
0.25
0.25
Oꢀ(16) 8e
!0.0248(7)C !0.0130(9)C 1.02(5)B 4D
example, for bismuth one should have y
"1!y
*(ꢀ) *(ꢁ)
. The examination of Table 2 shows that, even
and
z
"z
Space group
Cell parameters
a"5.4946(1) A
b"23.595(1) A
c"23.580(1) A
R factors
*(ꢀ) *(ꢁ)
R "0.037
if the above relations are not verified, the displacements
which violate these conditions remain small. This point will
be discussed further.
ꢀ
Pbnb (n°56)
R
"0.048
ꢁꢀ
R "0.057
It is interesting to compare the Bi—O plane (Fig. 6a) with
that observed in the ‘‘tubular 4’’ phase Bi Sr Cu O
(11, 12) (Fig. 6b). The Bi—O plane of the ‘‘tubular-2’’ phase
can be described as the analogous plane in the ‘‘tubular-4’’
phase with the zigzagging Bi—O chain characteristic of the
bismuth-based layered cuprates removed. The bismuth en-
?ꢋ@ꢋAꢋBParameters constrained at the same value.
CConstrain xꢀ"!x, yꢀ"!y.
ꢂ
ꢆ
ꢇ ꢁꢊ>W
DFull occupancy considered since value of ESD is greater than the
shifting.
vironment is similar to that of bismuth located at the border forming distorted octahedra characterized by four unequal,
of the Bi—O plane in the copper-based phase, i.e., three short equatorial Mn—O distances and two apical long dis-
approximately perpendicular Bi—O bonds considering only tances. Along b, one Mn(2) octahedron shares its corners
the short distances listed in Table 3. Among them, one with two other Mn(2) octahedra on one side and two Mn(1)
distance (1.85 A) is very short compared to the others and polyhedra on the other side. The same sequence is observed
smaller than those usually reported. However, Bi—O distan- along c for Mn(4) octahedra and Mn(3) polyhedra (Fig. 7).
ces as short as 1.74, 1.80, and 1.88 A, have already been The nature of the Mn(1) and Mn(3) polyhedra forming the
reported in Bi Ni O
ꢁꢆ ꢆ ꢃꢅ
(16), respectively.
The strontium—oxygen distances, which range between because the O—O distance would be too short (close to
(15), Bi Sr Fe O
(16), and pillars is more complex due to the presence of oxygens O(16)
ꢀ
ꢀ
ꢀ ꢊꢄꢀ
Bi Sr MnO
ꢅꢄꢀꢇ
and Oꢀ(16); they cannot coexist with the same x value
ꢀ
ꢀ
2.39 and 2.98 A, are comparable with those usually encoun- 1.3 A). This implies that the site occupancies cannot exceed
tered in layered cuprates.
50%; i.e., two oxygens per pillar or eight oxygens per unit
Manganese atoms, which do not participate to the pillar cell. Two possibilities occur depending on the position of
(Mn(2) and Mn(4)), are surrounded by six oxygen atoms oxygen atoms inside the pillar. If the pillar is occupied by

284
PELLOQUIN ET AL.
FIG. 5. Powder neutron diffraction patterns (j"1.5938 A) limited to 2h4100°; crosses refer to the experimental pattern, whereas the calculated and
difference patterns are drawn with hatched and solid lines respectively. The vertical bars indicate the Bragg angle positions.
one O(16) and one Oꢀ(16), for the reason given above, they latter model seems more likely than the former, which
necessarily have the same y and z values and differ only by generates two different Mn(1)O polyhedra and a parti-
ꢂ
x (0.25 and 0.75). In this configuration, the pillar can be cularly unusual connection (one common face) between two
described as built up from two edge-sharing distorted octahedra. So, from the second configuration, we can calcu-
Mn(3)O octahedra which share a face with a distorted late for each MnO polyhedron an average Mn—O distance
ꢅ
ꢅ
ꢂ
Mn(1)O octahedron on one side and one corner with (d) from which the manganese atoms can be listed in two
a Mn(1)O tetrahedron on the other side (Fig. 8a). If the groups: Mn(1) and Mn(2) with short (d) values (1.91 and
ꢂ
pillar is occupied by two oxygens O(16) (or two Oꢀ(16)), it 2.00 A, respectively); and Mn(3) and Mn(4) with longer (d)
can be described as built up from two edge-sharing distorted values (2.12 and 2.09 A, respectively). These values are close
Mn(3)O octahedra and Mn(1)O pyramids (Fig. 8b). The to those usually observed for Mnꢃ> in oxides (1.90—1.95 A
ꢅ
ꢇ
FIG. 6. Drawing of the bismuth-oxygen plane in (a) the ‘‘tubular-2’’ phase and (b) the ‘‘tubular-4’’ phase.

NEW MANGANITES Bi Sr
Mn O
285
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
TABLE 3
Interatomic Metal—Oxygen Distances (A)
Bi—O distances
Bi(1)—O(2)
Bi(1)—O(10)
Bi(1)—O(15)
;1 2.28(2)
;1 2.27(2)
;1 2.08(2)
Bi(2)—O(1)
Bi(2)—O(1)
Bi(2)—O(11)
Bi(2)—O(14)
;1 2.07(2)
;1 2.91(3)
;1 2.22(2)
;1 1.85(2)
Sr—O distances
Sr(1)—O(1)
Sr(1)—O(3)
Sr(1)—O(4)
Sr(1)—O(5)
Sr(1)—O(5)
Sr(1)—O(10)
Sr(1)—O(11)
Sr(1)—O(12)
;1 2.84(3)
;1 2.84(2)
;1 2.68(2)
;1 2.48(2)
;1 2.68(2)
;1 2.65(3)
;2 2.781(4)
;1 2.55(2)
Sr(4)—O(3)
Sr(4)—O(4)
Sr(4)—O(6)
Sr(4)—O(7)
Sr(4)—O(10)
Sr(4)—O(13)
Sr(4)—O(13)
Sr(4)—O(15)
Sr(4)—O(16)
Sr(4)—Oꢀ(16)
;1 2.67(2)
;1 2.83(2)
;1 2.46(2)
;1 2.44(2)
;1 2.84(2)
;1 2.69(3)
;1 2.82(3)
;1 2.65(3)
;1 2.85(2)
;1 2.85(2)
Sr(2)—O(2)
Sr(2)—O(3)
Sr(2)—O(4)
Sr(2)—O(5)
Sr(2)—O(5)
Sr(2)—O(10)
Sr(2)—O(10)
Sr(2)—O(11)
Sr(2)—O(13)
;1 2.45(2)
;1 2.85(2)
;1 2.69(2)
;1 2.65(2)
;1 2.44(2)
;1 2.72(3)
;1 2.86(3)
;1 2.50(2)
;1 2.91(2)
Sr(5)—O(1)
Sr(5)—O(6)
Sr(5)—O(7)
Sr(5)—O(8)
Sr(5)—O(9)
Sr(5)—O(12)
Sr(5)—O(14)
Sr(5)—O(14)
;1 2.39(2)
;1 2.82(2)
;1 2.85(2)
;1 2.809(2)
;1 2.809(2)
;1 2.58(2)
;1 2.74(2)
;2 2.804(5)
FIG. 7. Perspective view of a part of the manganese-oxygen frame-
work. The atoms are labeled. For simplicity the oxygens inside the pillar
are not drawn.
Sr(3)—O(3)
Sr(3)—O(4)
Sr(3)—O(6)
Sr(3)—O(7)
Sr(3)—O(11)
Sr(3)—O(12)
Sr(3)—O(14)
Sr(3)—O(16)
Sr(3)—Oꢀ(16)
;1 2.59(2)
;1 2.73(2)
;1 2.64(2)
;1 2.62(2)
;1 2.65(2)
;2 2.752(3)
;1 2.66(3)
;1 2.60(2)
;1 2.60(2)
Sr(6)—O(2)
Sr(6)—O(6)
Sr(6)—O(7)
Sr(6)—O(8)
Sr(6)—O(9)
Sr(6)—O(13)
Sr(6)—O(15)
Sr(6)—O(15)
Sr(6)—O(15)
;1 2.62(3)
;1 2.67(2)
;1 2.70(2)
;1 2.658(2)
;1 2.658(2)
;2 2.78(2)
;1 2.91(3)
;1 2.98(3)
;1 2.67(3)
Mnꢃ> in this compound agrees with the mean oxidation
state deduced from the oxygen stoichiometry refinements
(Table 2), which lead to Mnꢀꢄꢆꢊ>, assuming trivalent bis-
muth.
These calculations using the atomic positions of the Pbnb
space group allow two structural features related to the
positions of the Bi atoms and the oxygen atoms in the pillar
to be highlighted. Each of these points is discussed consider-
ing neutron analysis and HREM information.
Mn—O distances
Mn(1)—O(3)
Mn(1)—O(4)
Mn(1)—O(12)
Mn(1)—O(13)
Mn(1)—O(16)
Mn(1)—O(16)
Mn(1)—Oꢀ(16)
Mn(1)—Oꢀ(16)
;1 1.88(2)
;1 1.89(2)
;1 1.93(2)
;1 1.74(2)
;1 2.02(2)
;1 2.98(2)
;1 2.98(2)
;1 2.02(2)
Mn(3)—O(6)
Mn(3)—O(7)
Mn(3)—O(12)
Mn(3)—O(13)
Mn(3)—O(16)
Mn(3)—O(16)
Mn(3)—Oꢀ(16)
Mn(3)—Oꢀ(16)
;1 2.07(3)
;1 2.09(3)
;1 2.13(2)
;1 2.80(2)
;1 2.08(2)
;1 2.55(2)
;1 2.55(2)
;1 2.08(2)
(i) ¸attice distortion. [010] images clearly reveal the
lowering of the symmetry from the average F-type to the
actual P-type lattices (Fig. 9). Along [010], the experi-
mental contrast is very similar to that observed for the
Bi Sr MnO oxides, although the composition of the atom
ꢀ
ꢀ
ꢅ
columns is considerably more complex. For a focus value
close to !55 nm, the contrast consists of two rows of bright
spots, correlated to the projected positions of 2Bi, 2Sr and
1Mn atoms. They are sandwiched between two other rows
of bright spots, correlated to the projected positions of 4Sr
and 1Mn. These groups of four rows are separated by one
single row of small gray dots, which correspond to the Mn
positions. Theoretically, according to the F-type lattice,
these images would provide a periodicity of 2.7 A along b. In
Mn(2)—O(3)
Mn(2)—O(4)
Mn(2)—O(5)
Mn(2)—O(5)
Mn(2)—O(10)
Mn(2)—O(11)
;1 1.82(3)
;1 1.78(3)
;1 1.88(3)
;1 2.08(2)
;1 2.24(2)
;1 2.23(2)
Mn(4)—O(6)
Mn(4)—O(7)
Mn(4)—O(8)
Mn(4)—O(9)
Mn(4)—O(14)
Mn(4)—O(15)
;1 1.90(3)
;1 1.88(3)
;1 1.87(2)
;1 1.87(2)
;1 2.56(2)
;1 2.47(2)
for manganese in pyramidal coordination, 2.00 A or greater fact, a contrast modulation is observed locally at the level of
for Mn in octahedral coordination). Note that the mean the ‘‘double Bi’’ rows consisting of one bright dot alternat-
Mn(1)—O distance is close to that observed for MnO pyr- ing with one gray dot; this alternation is shifted by 2.7 A in
ꢇ
amids and supports the second model. The presence of the adjacent double row (this arrangement is outlined by

286
PELLOQUIN ET AL.
FIG. 8. Perspective view of the structure of the pillar. (a) If one O(16) and Oꢀ(16)) are present, it results in two edge-sharing Mn(3)O octahedra having
ꢅ
one face and one corner in common with a Mn(1)O octahedron and a Mn(1)O tetrahedron respectively (the common faces are outlined with dotted
ꢅ
ꢂ
lines). (b) In the case of two O(16) (or two Oꢀ(16)), the pillar is built with two edge-sharing Mn(3)O octahedra and two Mn(1)O pyramids (the common
ꢅ
ꢇ
edges are outlined with dotted lines).
dark circles in Fig. 9). This doubling of the periodicity along
b is in agreement with the small bismuth displacements
observed in the Pbnb space group with regard to the theor-
etical and ideal positions of the F-type structure. This
modulation is clearly observed in the calculated images.
A similar variation of contrast was reported by several
authors for the Bi cuprates (18) and manganites (19), and
correlated to the effect of the displacive modulation of the Bi
atoms. In the present structure, the incommensurate modu-
lation does not exist but is replaced by the periodic vari-
ation in the nature of the layers stacked along that direction,
due to the presence of the perovskite-related slice.
structure, i.e., the F-type lattice, there is a single position for
this oxygen, while in the Pbnb space group, two independent
positions are available. For the HREM image calculations,
one site of the oxygen in the pillar out of two was considered
fully occupied and the second vacant see Fig. 8b), in agree-
ment with the above structural discussion. The theoretical
images (labeled P in Fig. 3c) simulated for this model show
—
that a contrast similar to that experimentally recorded is
generated at the level of the pillar, i.e., the formation of
elongated bright dots, extended along the diagonal of the
‘‘pillar’’. The images calculated for focus values close to
!45 and !50 nm are compared directly with the equiva-
Note that this modulation is not observed over whole
crystals but only in the form of domains. This observation is
consistent with the superposition of the [010] and [001]
variants, as systematically observed form ED patterns (Fig. 1).
lent values for the Fmmm model (labeled F in Fig. 3c).
—
However, a difference remains between these calculated
images and the experimental images: the arrangement of the
elongated spots is perfectly ordered in the calculated images,
alternately elongated along [011] and [011], as a direct
consequence of the translations imposed by the space group
Pbnb, whereas they are often randomly distributed in the
experimental images. This point can be easily understood,
assuming that the oxygen site is partly occupied. The ran-
dom occupation, i.e., the superposition along a of the pos-
sible orientations of the double octahedra blocks and the
existence of twinning domains implies that the effect of
contrast asymmetry is no longer observed at the level of the
pillar as soon as the crystal thickness increases.
(ii) Structure of the pillar. The second point deals with
the problem of the oxygen located in the pillar and the
manganese polyhedra forming the cycle. In the average
Defective Structure
Most of the crystallites exhibit regular layer stacking;
only a few defects, such as the intercalation of extra layers or
shifting mechanisms, were detected.
The first type of defect corresponds to the formation of
n"4 members (Fig. 10a). Locally, the perovskite-related
FIG. 9. [010] HREM image showing the contrast modulation at the
level of the double (Bi, SrO) layers, correlated to the lowering of symmetry.
The alternation of bright and less bright dots along b is indicated by black
arrows, and the translation in the adjacent double layers is outlined by
black full circles.

NEW MANGANITES Bi Sr
Mn O
287
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
FIG. 10. [100] HREM images of defective areas: (a) example of n"4 member; (b) formation of shearing plane (the possible translation of this defect
along c is shown by white arrows); (c) idealized drawing of the two types of defects projected onto (100) plane. For simplicity only cations are drawn.
Bismuth atoms are schematized by medium circles whose the color depends on the x value (0 or 1/2).
the pseudotetragonal character of the n"2 ‘‘tubular’’ struc-
ture, in contrast with the higher-n members (of the cuprates),
where defects only arise, of course, along b.
The second type of defect indicated by white arrows
labeled ‘‘S’’ in Fig. 10b) results from a shifting of the struc-
ture at the level of the manganese layers. The amplitude of
slices [Sr Mn O
]
are separated by four (010)
ꢆ
ꢅ ꢁꢅ>B ꢉ
ꢅ ꢉ
[Bi Sr MnO ] slices; defective members are indicated in
ꢀ
ꢀ
the images by white arrows labeled 4, and the idealized
drawing is given in Fig. 10c. In some places, adjacent defec-
tive n"4 members are observed (see white arrow ‘‘4-4’’ in
Fig. 11); this can be considered a favorable sign for the
stabilization of the n"4 member. Another interesting point
is that the defects occur along two perpendicular directions
(see white arrow labelled ‘‘4N’’ in Fig 11). The fact that
defective members arise equally along b and c emphasizes
the translation is about a (2/2. As a result, the manganese
ꢀ
layers perpendicular to the direction of translation are no
longer facing but connected to one (010) [Sr MnO ] layer.
ꢂ
ꢅ ꢉ
One (010) [Bi Sr MnO ] layer out of two is connected to
ꢀ
ꢀ
ꢅ ꢉ

288
PELLOQUIN ET AL.
FIG. 11. Overall [100] image of a crystallite exhibiting a high density of defects.
another (010) [Bi Sr MnO ] layer, whereas the second is open white arrows labeled 3 in Fig. 10b), whereas they were
ꢅ ꢉ
connected to one [Sr MnO ] layer (a schematic drawing never observed in the form of ‘‘stabilized’’ defective slices. This
ꢀ
ꢀ
ꢂ
ꢅ ꢉ
is given in Fig. 10c). Similar defects were previously reported behavior is similar to that observed in the cuprates, where
in the ‘‘tubular’’ cuprates (13, 20, 21) and were also observed the n(4 members were not observed, except in defective
to be formed periodically in the so-called ‘‘monoclinic tubu- areas where the shearing mechanism is translated (13).
lar’’ phases for the n"7 member (21) and the Li-doped
cuprates (22). In such a defect, the pillars are destroyed
because the manganese layers no longer cross over a single
point. In this ‘‘tubular-2’’ manganite, shearing planes are
TRANSPORT AND MAGNETIC PROPERTIES
This new phase is an insulator characterized by a very high
also observed along two perpendicular b and c directions. resistivity even at room temperature (o
' 10ꢅ )/cm). In
ꢃꢈꢈ)
The intergrowth and shearing mechanisms are formed order to get more information concerning its physical proper-
without any strong distortion of the structure. This can be ties, magnetic susceptibility s(¹) measurements (Faraday
observed in the overall image (Fig. 11) of a rare crystallite method) in 3 kG were also performed. In Fig. 12, the s(¹)
which exhibits a particularly, high density of defects. More- curve in the range 100—800 K (labeled a) is reported, while
over, it can be observed that the (010) or (001) shearing s\ꢁ(¹) values up to 400 K are plotted in the inset, with the
planes are easily translated along one of the perpendicular solid line corresponding to a fit from a Curie-Weiss law:
directions (compare the levels of the long white arrows, which
are at the level of the manganese layers on both sides of the
s"s #C/(¹!hp).
ꢈ
shearing plane in Fig. 10b) or even propagated along inclined The effective moment per manganese deduced from this fit,
directions as the result of successive translations (Fig. 11). k "4.7 k , is close to that expected for high-spin Mnꢃ>
%&&
The two types of defects, higher n members and shearing (k
"4.9 k ). This value is consistent with the valence
ꢃ)%ꢄꢅ*ꢃ*#!ꢆ
planes, are often coupled, facilitating their accommodation state of manganese (#2.89) inferred from the chemical for-
by the framework. As an example, a n"4 member formed mula deduced from neutron data refinements. Moreover
perpendicular to a shearing plane is drawn in Fig. 10c. The this fitting also leads to a negative hp value, hp"!650 K,
width difference between the n"4 member and the n"2 characteristic of dominant antiferromagnetic interactions
regular matrix is accommodated by the fact that the transla- between magnetic Mnꢃ> species. A comparative study per-
tion vectors (correlated to the shearing mechanisms) are in formed on the parent 2201 structure Bi Sr MnO , syn-
ꢀ
ꢀ
ꢅ>B
opposite directions in the two parts of the matrix separated thesized in the same experimental conditions as the n"2
by the defective n"4 member.
tubular, shows that the s values for this new manganite
A last remark deals with the fact that n"3 members can be are deeply depressed. The peak observed on the s(¹) curve
formed at the level of the translation of the shearing plane (see (labeled b in Fig. 12) of the 2201 phase is in agreement with

NEW MANGANITES Bi Sr
Mn O
289
ꢃꢄꢅ ꢁꢀꢄꢂ
ꢆ
ꢀꢆ>B
The extended defects observed by HREM, although rare,
are of great interest. They suggest that new members in this
series, as well as other original structures, may be syn-
thesized by applying shearing mechanisms.
ACKNOWLEDGMENTS
The authors are grateful to Dr. E. Suard (Institut Laue-Langevin,
Grenoble, France) for the neutron diffraction facilities and to Dr. N.
Nguyen for susceptibility measurements.
REFERENCES
1. J. G. Bednorz and K. A. Muller, Z. Phys. B 64, 189 (1986).
2. See for example R. Von Helmolt, J. Wecker, B. Holzapfel, L. Schultz,
and K. Sanwer, Phys. Rev. ¸ett. 71, 2331 (1993).
3. C. Michel, M. Hervieu, M. M. Borel, F. Deslandes, J. Provost, and
B. Raveau, Z. Phys. B 68, 421 (1987).
4. M. Maeda, Y. Tanaka, M. Fukutomi, and T. Asano, Jpn. J. Appl. Phys.
L27, 209 (1988).
5. M. A. Subramanian, C. C. Torardi, J. C. Calabrese, J. Gopalakrishnan,
K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry, and A. W.
Sleight, Science 2398, 1015 (1988).
6. J. M. Tarascon, Y. Le Page, P. Barboux, B. G. Bagley, L. H. Greene,
W. R. McKinnon, G. W. Hull, M. Giroud, and D. M. Hwang, Phys.
Rev. B 37, 9382 (1988).
FIG. 12. Molar susceptibility magnetic s(¹) registered in 3 kG for a)
Bi Sr Mn O
and b) Bi Sr MnO
. The inset shows the s\ꢁ(¹)
ꢂ
ꢁꢀ
ꢆ
ꢀꢆ>B
ꢀ
ꢀ
ꢅ>B
values between 100 and 400 K and the corresponding data to the fitting
from Curie-Weiss law (solid line).
7. W. R. McKinnon, E. Tselepsis, Y. Le Page, S. P. McAlister, G. Pleizier,
J. M. Tarascon, P. F. Miceli, R. Ramesh, G. W. Hull, J. V. Waszczak,
J. J. Rhyne, and D. A. Neumann, Phys. Rev. B 41, 4489 (1990).
8. R. S. Roth, C. J. Rawn, and I. A. Bendersky. J. Mater. Res. 5, 46 (1990).
9. Z. Hiroi, Y. Ikeda, M. Takano, and Y. Bando, J. Mater. Res. 6, 435
(1991).
previously reported data (7) and was correlated to ferro-
magnetic behavior. The strong decrease of the s values in
the case of the n"2 tubular phase suggests that long-range
magnetic order cannot develop. This feature is not surpris-
ing if one considers that this tubular structure exhibits
10. M. Hervieu, C. Michel, A. Q. Pham, and B. Raveau, J Solid State Chem.
104, 338 (1993).
several kinds of MnO polyhedra at the level of pillars. The
L
11. A. Fuertes, C. Miratvilles, J. Gonzalez-Calbet, M. Vallet-Regi, X.
Obradors, and J. Rodriguez-Carvajal, Physica C 157, 529 (1989).
12. M. T. Caldes, J. M. Navarro, F. Perez, M. Canera, J. Fontuberta, M.
Casan-Pastor, C. Miratvilles, X. Obradors, J. Rodriguez-Carvajal,
J. M. Gonzalez-Calbet, M. Vallet-Regi, A. Garcia, and A. Fuertes,
Chem. Mater. 3, 844 (1991).
13. M. T. Caldes, M. Hervieu, A. Fuertes, and B. Raveau, J. Solid State
Chem. 97, 48 (1992).
14. J. Rodriguez-Carvajal, in ‘‘Satellite Meeting on Powder Diffraction,’’
p. 127. Abstracts of the XVth Conference of the International Union of
Crystallography, Toulouse, 1990.
overlaping Mn—O orbitals are thus periodically modified,
leading to the localization of the charge carriers. Accord-
ingly the long-range ordering of the manganese magnetic
moment is broken. The result is an insulating compound
exhibiting weak antiferromagnetism.
CONCLUDING REMARKS
This study shows the ability of manganese oxides to form
‘‘tubular’’ structures, reinforcing the structural analogy be-
tween manganese and copper oxides. Nevertheless this man-
ganite differs from the previously isolated cuprates in the
15. A. Ramnan, J. Gopalakrishnan, and C. N. R. Rao, Mater. Res. Bull. 16,
169 (1981).
16. Y. Le Page, W. R. McKinnon, J. M. Tarascon, and P. Barboux, Phys.
Rev. B 40, 6810 (1989).
fact that the ‘‘Mn ’’ pillars formed by the criss-crossing 17. J. M. Tarascon, Y. Le Page, W. R. McKinnon, E. Tselepis, P. Barboux,
ꢂ
B. G. Bagley, and R. Ramesh, Mater. Res. Soc. Symp. Proc. 156, 317
(1989).
18. H. W. Zandbergen, W. A. Groen, F. C. Mijlhoff, G. Van Tendeloo, and
S. Amelincks, Physica C 156, 325 (1988).
19. M. Hervieu, C. Michel, D. Pelloquin, A. Maignan, and B. Raveau,
J. Solid State Chem. 132, 420 (1997).
20. B. Domenges, M. T. Caldes, M. Hervieu, A. Fuertes, and B. Raveau,
Microsc. Microanal. Microstruct. 3, 415 (1992).
21. M. T. Caldes, M. Hervieu, A. Fuertes, and B. Raveau, J. Solid State
Chem. 98, 45 (1992).
layers of manganese contain more oxygen. In other words,
both series of oxides can be described as the intergrowth of
‘‘2201’’ type slices [Bi Sr MO ] with [Sr M O
cient, perovskite-related slices (M"Cu, Mn).
An interesting feature deals with the fact that this n"2
member stabilized for manganese has not been observed for
copper. But most interesting is the fact that it is the only
member of the series that exhibits ‘‘2201’’ types slices
oriented at 90°, i.e., parallel to (010) and (001), in agreement
with its pseudotetragonal symmetry.
]-defi-
ꢀ
ꢀ
ꢅ L
ꢆ
ꢅ ꢁꢅ>B
22. G. Van Tendeloo, B. Domenges, M. T. Caldes, M. Hervieu, and
B. Raveau, J. Solid State Chem. 112, 16 (1994).