Crystal structure and magnetic properties of a new iron(III) silicophosphate FE3P5SiO19 studied by neutron diffraction and Moessbauer techniques

Article abstract of DOI:10.1006/jssc.2001.9449

Fe₃P₅SiO₁₉ has been prepared by solid state reaction of Fe(PO₃)₃, FePO₄, and SiO₂ at 1000°C. The structure has been determined from a single crystal through direct methods and difference Fourier synthesis and refined to R = 0.052. The unit cell is hexagonal, space group P6₃, with a = 14.4804(8) A, c = 7.4256(2) A, and Z = 4. The three-dimensional framework is built up from [Fe₂O₉] units of two faces sharing octahedra and Si₂O₇ disilicates linked by PO₄ tetrahedra. Fe₃P₅SiO₁₉ is isotypic with V₃P₅SiO₁₉. Fe₃P₅SiO₁₉ is antiferromagnetic below T_N= 35 K. The magnetic structure has been determined by means of powder neutron diffraction methods: the magnetic moments are antiferromagnetically coupled inside the [Fe₂O₉] units, in agreement with the Goodenough rules. These units are linked to each other through several Fe-O-P-O-Fe super-superexchange pathways and form antiferromagnetic [001] rows. The moment direction lies in the (001) plane (μ_Fe = 4.56(5) μ_B at 2K). There is a competition between the intra- and interunits interactions which all are antiferromagnetic and cannot be simultaneously satisfied without frustration. Moessbauer spectra are fitted with two doublets and two sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect. The magnetic interactions are discussed.

Full text of DOI:10.1006/jssc.2001.9449

Journal of Solid State Chemistry 164, 71}80 (2002)
doi:10.1006/jssc.2001.9449, available online at http://www.idealibrary.com on
Crystal Structure and Magnetic Properties of a New Iron(III)
Silicophosphate Fe P SiO Studied by Neutron Diffraction
3
5
19
and Mo
K
ssbauer Techniques
L. K. Elbouaanani,* B. Malaman,* R. G eH rardin,*ꢁꢀ and B. Ouladdiaf-
*
Laboratoire de Chimie du Solide Min e& ral, Universit e& Henri Poincar e& -Nancy 1, associ e& au CNRS (UMR 7555), B.P. 239, 54506 Vandoeuvre-les-Nancy Cedex,
France; and -Institut Laue-Langevin, B.P. 156, 38042 Grenoble Cedex 9, France
Received July 10, 2001; in revised form October 25, 2001; accepted November 9, 2001
iron(III) silicophosphate: Fe P SiO . This work shows
ꢂ ꢅ
ꢂ ꢅ ꢀꢆ
ꢀꢆ
Fe
Fe(PO
3
P
3
5
SiO19 has been prepared by solid state reaction of that it is isotypic with V P SiO whose the crystallo-
)
3
, FePO
4
, and SiO at 10003C. The structure has been graphic structure was established by Leclaire et al. (3).
2
determined from a single crystal through direct methods and
di4erence Fourier synthesis and re5ned to R ؍ 0.052. The unit
There also exists Mo P SiO synthesized by Wang et al.
ꢂ ꢅ ꢀꢆ
(
4) but the crystallographic structure of Mo P SiO di!ers
ꢂ ꢅ ꢀꢆ
cell is hexagonal, space group P6
c ؍ 7.4256(2) A, and Z ؍ 4. The three-dimensional framework is
built up from [Fe ] units of two faces sharing octahedra and
Si disilicates linked by PO tetrahedra. Fe SiO19 is isotypic
with Fe SiO19 is antiferromagnetic below
؍ 35 K. The magnetic structure has been determined by
means of powder neutron di4raction methods: the magnetic
moments are antiferromagnetically coupled inside the [Fe
3
s
, with a ؍ 14.4804(8) A,
from that of V P SiO in the position of one P atom. These
two compounds crystallize in the space group P6 with
ꢂ ꢅ
ꢀꢆ
s
O
9
ꢂ
2
Z"4. V(III) and Mo(III) are in confacial bioctahedral
2
O
7
4
3
P
5
units [V O ] and [Mo O ] where V}V and Mo}Mo dis-
V
3 5
P SiO19
.
3
P
5
ꢃ ꢆ
ꢃ ꢆ
tances are rather short; for the latter Wang et al. (4) expect
a Mo}Mo bond.
T
N
O
2 9
]
In this Paper, we present the crystallographic and mag-
units, in agreement with the Goodenough rules. These units are netic structures of Fe P SiO determined by means of
ꢂ ꢅ ꢀꢆ
linked to each other through several Fe+O+P+O+Fe super- single-crystal X-ray di!raction, bulk magnetization, powder
superexchange pathways and form antiferromagnetic [001]
rows. The moment direction lies in the (001) plane (ꢀFe ؍ 4.56(5)
neutron di!raction, and Mo
ments. It will be interesting to compare the magnetic struc-
ture of Fe P SiO to those of V P SiO and
K ssbauer spectroscopy experi-
ꢀ
B
at 2 K). There is a competition between the intra- and in-
terunits interactions which all are antiferromagnetic and cannot
be simultaneously satis5ed without frustration. Mossbauer
ꢂ ꢅ
ꢀꢆ
ꢂ ꢅ
ꢀꢆ
Mo P SiO , which are not yet known today.
4
ꢂ ꢅ ꢀꢆ
spectra are 5tted with two doublets and two sextuplets in the
paramagnetic and antiferromagnetic states, respectively. Their
rather high isomer shifts are explained by the inductive e4ect.
The magnetic interactions are discussed. ꢀ 2002 Elsevier Science (USA)
Key Words: iron silicophosphate; crystal structure; neutron dif-
EXPERIMENTAL
Fe P SiO has been obtained from the &&Fe(PO ) /
ꢂ ꢅ ꢀꢆ ꢂ ꢂ
5
7
FePO /SiO '' mixture in adequate proportions, annealed
fraction; magnetic structure; Fe M o4 ssbauer spectrometry.
ꢄ
ꢃ
for 3 days at 10003C, in a silica tube. The starting com-
pounds were prepared as follows.
Fe(PO ) and FePO were obtained from a solution of
ꢂ ꢂ
ꢄ
INTRODUCTION
Fe(NO ) ) 9H O and H PO (in the ratio Fe/P"ꢀ and
ꢂ ꢂ
Fe/P"ꢀ, respectively), which was evaporated, and then
ꢃ
ꢂ
ꢄ
ꢂ
ꢀ
In the Fe}P}Si}O system, only two phases have been annealed at 4003C under nitrogen for 24 h and "nally an-
known until now: iron(III) FeP SiO studied by El- nealed at 9003C under oxygen.
ꢂ
ꢀꢀ
bouaanani et al. (1) and iron(II) Fe SiP O described by
ꢄ ꢀꢄ
SiO was obtained from silicic acid SiO ) xH O annealed
at 1203C to eliminate water and then annealed at 8003C for
ꢃ
ꢃ
ꢃ
ꢃ
Glaum and Schmidt (2).
In the course of an investigation of mixed-valent iron 12 h.
phosphates and silicophosphates, we have discovered a new
Single crystals were grown by long annealing (1 month)
in sealed silica tubes within a gold crucible, under vacuum,
at 10003C, with traces of FeCl as mineralizing agent.
A single crystal (ꢀ&100 ꢀm) was selected for the structure
ꢀ
To whom correspondence should be addressed. E-mail: Rene.
ꢃ
Gerardin@lcsm.uhp-nancy.fr.
7
1
0
022-4596/02 $35.00
ꢀ
2002 Elsevier Science (USA)
All rights reserved.

7
2
ELBOUAANANI ET AL.
determination. The data were collected on a Nonius
TABLE 2
Kappa-CCD area detector di!ractometer at the Service
Atomic Coordinates and Thermal Agitation Factors
for Fe P SiO
Commun de Di!ractome
H
trie de l'Universite
H
Henri Poin-
3
5
19
care-Nancy I.
H
Atom
Site Symmetry
x
y
z
s
B(Aꢃ)
Magnetic measurements were performed (between 4.2
and 300 K) on a MANICS magnetosusceptometer in "elds
up to 1.6 T.
Neutron di!raction experiments were carried out at the P(1)
Institut Laue Langevin, Grenoble. Several di!raction pat-
terns were recorded with the one-dimensional curved multi-
detector D1B using a neutron wavelength of 2.520 A
temperature range 100}2 K. The analysis of the patterns
was performed by Rietveld pro"le re"nements (5) using the O(1)
software Fullprof (6).
The M oK ssbauer data were collected with a constant accel-
eration spectrometer with 1024 channels. Isomer shifts are
reported with respect to ꢁ-iron at room temperature (line
width"0.25 mm/s). The Mo
lyzed by using least-squares minimization techniques (7) to
evaluate the hyper"ne spectral parameters.
Fe(1)
Fe(2)
6c
6c
6c
6c
6c
2a
2b
2b
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
2a
2b
1
1
1
1
1
3
3
3
1
1
1
1
1
1
1
1
1
1
1
1
3
3
0.3409(5)
0.3411(4)
0.0173(5)
0.0182(5)
0.1892?
0.79(8)
0.79(8)
0.7826(4)
0.1466(3) !0.0868(3)
0.4329(3) 0.2120(3)
0.4864(17) 0.58(6)
0.4875(17) 0.66(6)
0.4852(18) 0.59(6)
0.4503(18) 1.18(16)
0.5274(19) 1.26(24)
0.4590(17) 0.95(16)
0.1551(24) 0.01(3)
0.4851(38) 0.55(16)
0.1552(30) 1.03(39)
0.4841(43) 0.47(16)
0.4953(31) 0.47(24)
0.3108(32) 1.97(47)
0.4746(36) 1.50(24)
0.3270(29) 1.10(39)
0.3113(30) 1.66(47)
0.1686(33) 1.10(39)
0.0213(23) 1.03(24)
0.0264(21) 1.26(31)
P(2)
P(3)
0.4228(3) !0.0957(3)
P(4)
0
0
s
, in the
Si(1)
Si(2)
ꢃ
ꢀ
ꢂ
ꢂ
ꢀ
ꢃ
ꢂ
ꢂ
0.2516(13)
0.2110(13)
O(2)
0.3634(8)
0.4512(16)
0.6955(8)
0.0600(8)
0.2005(18)
0.6918(9)
0.4228(16)
0.0719(17)
0.2655(17)
0.1181(9)
0.6402(10)
0
0.2657(7)
0.3969(16)
0.9042(7)
0.6021(8)
0.9660(18)
0.2440(9)
0.1515(16)
0.4573(17)
0.4148(17)
0.0493(9)
0.2198(10)
0
O(3)
O(4)
O(5)
O(6)
K
ssbauer e!ect data were ana- O(7)
O(8)
O(9)
O(10)
O(11)
O(12)
O(13)
O(14)
STRUCTURE DETERMINATION
0.240(15)
1.7(9)
ꢃ
ꢂ
ꢀ
ꢂ
0.7411(40) 1.26(47)
The cell parameters, initially measured on Guinier pat-
tern, were re"ned by di!ractometric techniques at 203C with
least-squares re"nement based on 25 re#ections and are
?Atom used to "x the origin of the cell
a"14.4804(8) A
From the data collection containing 5840 re#ections,
95 with I'3ꢄ(I) were considered for the structural limiting possible re#ections (00l with l"2n) was between
resolution. P6 , P6 /m, and P6 22.
s s
, c"7.4256(2) A in the hexagonal system.
The choice of space group according to the conditions
8
ꢂ
ꢂ
ꢂ
The conditions for the data collection and re"nement of
the structure are listed in Table 1. All computer programs
used were taken from Ref. (8). Absorption was corrected by
the Sortav software (9). Scattering factors for Fe, P, Si, and
O were taken from the International ¹ables for X-ray Crys-
tallography (10).
TABLE 1
Summary of Data Collection and Structure Re5nement
of Fe P SiO
3
5
19
Molar mass (g.mol\ꢀ)
Crystal size (ꢀm)
Symmetry
654.49
ꢁ+100
Hexagonal
14.4804(8)
7.4256(2)
1347.39
4
3.251
P6
MoKꢁ
Graphite
The structure was re"ned satisfactorily in the space group
P6 . The iron, phosphorus, and silicon atom positions have
a (A
c (A
s
)
)
ꢂ
been obtained using the direct methods procedure of the
Shelx program (8). The oxygen atom positions were deter-
mined by di!erence Fourier synthesis. Final re"nement with
individual and isotropic temperature factors leads to the
s
<
Z
ꢀ
(A
(g.cm\ꢂ)
ꢁꢂ
s
ꢂ)
ꢀ
Space group
ꢂ
reliability factors R"0.052 (R "0.052). The atomic
Radiation
Monochromator
Scan mode
ꢃ
parameters are listed in Table 2 and the main interatomic
distances and angles are given in Table 3.
Oscillation scan
ꢂ425
Record limits (3)
Linear absorption coe$cient ꢃ (mm\ꢀ) 133.67
STRUCTURE DESCRIPTION
Recorded intensities
5840
Unique and nonzero intensities
Recorded intensities with ꢄ(I)/I(0.33 895
F(000)
2078
The crystal structure of Fe P SiO is a three-dimen-
ꢂ ꢅ
ꢀꢆ
1276
sional network of corner-sharing [Fe O ] units, PO tet-
ꢃ ꢆ
ꢄ
Index ranges
04h414. 04k414.!74l47 rahedra, and disilicate Si O groups (Fig. 1). The [Fe O ]
79
0.052
0.052
ꢃ ꢇ
ꢃ ꢆ
Number of parameters
Final R value
Final wR2 value
unit is formed by pair of FeO octahedra sharing a face;
ꢈ
the Si O disilicate group is formed by a pair of SiO
tetrahedra sharing an apex and exhibiting a semieclipsed
ꢃ ꢇ
ꢄ

STRUCTURE AND PROPERTIES OF Fe P SiO
ꢂ ꢅ ꢀꢆ
73
TABLE 3
The [Fe O ] units and the Si O disilicates are along
in"nite rows parallel to the c axis, connected to each other
ꢃ ꢆ
ꢃ ꢇ
Main Interatomic Distances (A
s
) and Angles (3) for Fe P SiO
3
5
19
by PO tetrahedra (Fig. 2).
ꢄ
[
FeO ] octahedra
The two FeO octaedra are distorted. They exhibit three
ꢈ
ꢈ
Fe(1)}O(9)
Fe(1)}O(8)
Fe(1)}O(6)
Fe(1)}O(5)
Fe(1)}O(2)
Fe(1)}O(4)
Fe(1)}O
1.93(2)
1.98(2)
2.00(2)
2.06(2)
2.11(2)
2.12(2)
2.03
Fe(2)}O(10)
1.85(3)
1.87(2)
1.89(2)
2.09(2)
2.11(2)
2.17(2)
2.00
short distances Fe}O, 1.85 to 2.00 A
s
, values smaller than the
Fe(2)}O(3)
Fe(2)}O(1)
Fe(2)}O(4)
Fe(2)}O(2)
Fe(2)}O(5)
Fe(2)}O
2
s
.015 A calculated by Brown and Altermatt (11) for the
bond length Feꢂ>}Oꢃ\. Three longer distances, 2.06 to
ꢄꢀꢅ
2.17 A, connect each Fe atom to the three O atoms O(2),
s
O(4), and O(5) of the shared face (see Table 3).
The distance Fe}Fe (3.019 A) is comparable to 2.967 and
.048A , values found in Fe (P O ) by Elbouaanani et al.
s
Fe(1)}Fe(2)
3.019(3)
3
(
s
ꢄ
ꢃ ꢇ ꢂ
12), and 2.99 A found in the Fe (PO ) (OH) hy-
ꢄ ꢂ
droxyphosphate compound by Ijjaali et al. (13).
[
PO ] Tetrahedra
s
ꢄ
ꢄ
ꢂ
P(1)}O(1)
P(1)}O(6)
P(1)}O(4)
P(1)}O(11)
P(1)}O
1.50(2)
P(2)}O(8)
1.44(2)
1.55(1)
1.57(3)
1.59(2)
1.54
1.52(2)
1.54(1)
1.58(1)
1.54
P(2)}O(2)
P(2)}O(10)
P(2)}O(7)
P(2)}O
Face-sharing between octahedra is much less common in
iron compounds than edge-sharing, because it brings ca-
tions very close to each other and this destabilizes the
lattice. But for this compound, as we are dealing with
distorted octahedra, the Feꢂ>ions move in such a way that
P(3)}O(9)
P(3)}O(3)
P(3)}O(5)
P(3)}O(12)
P(3)}O
1.51(2)
1.52(2)
1.54(1)
1.59(1)
1.54
P(4)}O(13)
P(4)}O(11);3
1.56(11)
1.58(1)
s
they increase their distance from each other to 3.019 A,
which is comparable to what we have in edge-sharing
octahedra.
P(4)}O
1.56
Simultaneously, oxygen ions move within the shared face
toward each other in order to screen the Feꢂ>}Feꢂ> repul-
sion. The mean oxygen}oxygen distance is signi"cantly
[
SiO ] Tetrahedra
ꢄ
Si(1)}O(7);3
Si(1)}O(14)
Si(1)}O
1.56(2)
1.59(3)
1.58Si(2)
Si(2)}O(12);3
Si(2)}O(14)
}O
1.57(2)
1.62(3)
1.58
smaller in the shared face, O}O"2.55 A
O(2)}O(4)}O(5), whereas O}O"2.99 A
O(9)}O(8)}O(6) face and 2.83 A
face (see Fig. 2).
s
between
between
for the O(1)}O(3)}O(10)
s
Angles
s
Si(1)}O(7)}P(2)
P(4)}O(11)}P(1)
139(1)
141(1)
Si(2)}O(12)}P(3)
Si(1)}O(14)}Si(2)
146(1)
180
The P(4) atom (special position (2a), Table 2) is in tetra-
hedra obviously aligned along the c axis. Each P(4)O
tetrahedron connects its three apices O(11) with three
ꢄ
con"guration. The six terminal oxygen atoms of Si O are P(1)O tetrahedra, and the fourth apex O(13) is &&free''
ꢃ ꢇ
ꢄ
ꢄ
bonded to six surrounding PO tetrahedra: three P(2)O and (O(13) is only bound to P(4)) (Figs. 3 and 4a); in this way
ꢄ
three P(3)O , forming the [Si P O ] silicophosphate unit. these four tetrahedra form the [P O ] unit. This situation
ꢄ
ꢃ ꢈ ꢃꢅ ꢄ ꢀꢂ
Fe2
P2
P4
P4
Fe1
P1
P1
P3
P1
P2
P3
Fe1
Fe1
Si2
Fe1
P2
P3
P3
P2
P1
P3
Si1
Fe2
P1
Fe2
Fe2
P2
P2
P3
P1
Fe2
P4
Fe1
P4
FIG. 1. Projection of the framework of Fe P SiO along [001].
ꢂ ꢅ ꢀꢆ

7
4
ELBOUAANANI ET AL.
O8
O6
O9
O6
O8
O9
Fe1
O9
O14
O10
O8
Fe1
O6
Fe1
O10
O5
O7
P2
Si1
Fe2
P2
O2 P2
O8
O4
O4
O5
O1
Fe2
Fe2
O3
P3
Fe1
O8
O3
O9
O10
O8
O3
P3
O1
O5
O12
Si2
O10
O12
O12
P3
Fe2
Fe2
O5
O9
O6
Fe1
Fe1
O6
O10
O14
O8
Fe1
O10
Si1
Fe2
O8
P2
P2
O2 P2
O8
O7
O5
O4
O4
Fe2
Fe2
O5
O3
O1
O3
O10
O12 P3
O10
O12
c
O12
Si2
O4
P3
P3
Fe2
Fe2
O5
O9
O9
O10
O10
O14
O1
a
O3
b
FIG. 2. Clinographic view showing the connections between Si O and [Fe O ] units via P(2)O and P(3)O tetrahedra.
ꢃ
ꢇ
ꢃ
ꢆ
ꢄ
ꢄ
O9
O8
O8
O5
O6
O6
O9
Fe1
O1
O1
Fe1
P1 O1
O11
O11
O4
O5
O4
Fe2
P1
O2
Fe2
O8
O11
P4
P1
Fe1
O9
O6
O6
O8
Fe1
O1
O13
O9
O3
O9
P1
P1
O2
O11
O11
Fe1
P1
O11
O5
P4
O5
O4
c
O2
O3
Fe2
Fe2
O13
O1
O1
O3
O1
O10
O4
O2
O5
O4
O3
O2
O5
a
b
FIG. 3. Clinographic view showing the connections between P(4)O and [Fe O ] units via P(1)O tetrahedra.
ꢄ
ꢃ
ꢆ
ꢄ

STRUCTURE AND PROPERTIES OF Fe P SiO
75
ꢂ ꢅ
ꢀꢆ
P1
P1
P1
P1
P3
P1
P1
P4
P4
P3
Si2
Si1
P3
P1
P1
P1
P1
P4
P2
P2
P1
P1
P2
P4
(
c)
(b)
(a)
FIG. 4. (a) Real [P O ] unit. (b) Hypothetical [P O ] unit. (c) Real [Si P O ] unit.
ꢀꢂ ꢃꢅ ꢃ ꢈ ꢃꢅ
ꢄ
ꢉ
is not usual, it is also found in V P SiO (3). The three also exists in Mo P SiO but was interpreted di!erently by
ꢂ ꢅ ꢀꢆ ꢂ ꢅ ꢀꢆ
distances P(4)}O(11)"1.58(1) A
P(4)}O(13)"1.56(11) A
respectively three 1.517(5) and one 1.54(4) A
cases the low accuracy on the distance values P}O can be these structural determinations should re#ect a structural
explained by a high thermal agitation. This phenomenon disorder on this point.
s
seem to be longer than Wang et al. (4): two sites P(4) and Pꢅ(4), 0.55 A
s
apart, with
s
(it is the opposite in V P SiO the occupancy factors 0.55 and 0.45 are used to place this
:
ꢂ ꢅ ꢀꢆ
s
). In the two P atom in the cell. Whatever way we look at the problem,
ꢆꢇꢈꢈ
Two adjacent P(4)O groups are eclipsed (see Fig. 1) and,
ꢄ
like in [Si P O ], [P O ] connects [Fe O ] units
ꢃ ꢈ ꢃꢅ
ꢄ ꢀꢂ
ꢃ ꢆ
1
0
30
50
70
90
110
130
150
0.15
(Fig. 3).
The P}O distances for P(1), P(2), and P(3) are classical
(Table 3), and the average values (1.54 A) are comparable to
1
4
13
12
11
10
s
the 1.536 A
s
value given by Corbridge (14). The longest P}O
distances are observed for O common to the PO and SiO
tetrahedra, and the same is found for the other silicophos-
phates (15}17).
0
0
.13
.11
ꢄ
ꢄ
The angles Si}O}P involving an oxygen atom bridging
two tetrahedra range from 143(1) to 156(2)3, close to the
values found in V P SiO (3) (134.9(2) and 151.1(4)3).
9
8
7
6
ꢂ ꢅ
ꢀꢆ
ꢄ ꢀꢂ
0
0
.09
.07
The staking of the [P O ] units along the c axis shows
that the simple migration of one central phosphorus atom
along the P(4)}P(4)--- row (Fig. 4a) would lead to the
[P O ] units (Fig. 4b). This hypothetical unit does not
exist in iron phosphates. The replacement of the two central
1
40
4
0
60
80
T (K)
100
120
ꢉ ꢃꢅ
(
a)
phosphorus atoms by silicon in the [P O ] allows the
ꢉ ꢃꢅ
formation of a [P Si O ] unit (Fig. 4c). A framework built
0
.6
ꢈ ꢃ ꢃꢅ
T = 8 K
up from of [M O ] dimers and only [P Si O ] units
ꢃ ꢆ
ꢄ ꢈ ꢃ ꢃꢅ
but not for M"Fe.
ꢈ ꢃ ꢃꢅ
0
.5
exists with the M P Si O composition for M"Mo (17),
0
0
.4
.3
These results show that Fe P SiO is isotypic with
ꢂ ꢅ
ꢀꢆ
V P SiO (3).
ꢂ ꢅ ꢀꢆ
0
0
.2
.1
MAGNETICSTUDY
H # 6 kG
(
a)Susceptibility Measurements
0
.0
The thermal variation of the susceptibility is shown in
0
2
4
6
8
10 12 14 16 18
Fig. 5a. Fe P SiO is antiferromagnetic below ¹ "35 K.
(
b)
ꢂ ꢅ
ꢀꢆ
,
H(kG)
In the paramagnetic state, the Curie}Weiss law is obeyed,
leading to the Curie molar constant C "15.66, which
FIG. 5. (a) Temperature dependence of the inverse susceptibility of
Fe P SiO , (b) Magnetization versus applied "eld of Fe P SiO at 8K.
+
corresponds to 6.46 ꢃ for the e!ective magnetic moment
ꢂ ꢅ
ꢀꢆ
ꢂ ꢅ
ꢀꢆ

7
6
ELBOUAANANI ET AL.
per iron atom. This value is higher than 5.9 ꢃ expected for
The extrapolated Curie temperature is negative:
a high-spin iron(III) cation. We have no explanation to ꢂ "!63 K.
ꢉ
interpret this di!erence; however, we have noted that this
The measurement of the magnetization versus "eld at 8K
fact is currently observed for iron(III) phosphate com- is shown in Fig. 5b. The magnetization increases linearly at
pounds, as the results below show:
low "eld, and then it changes slope at about H"6 kG. Such
behavior may be characteristic of a metamagnetic-like
transition.
Fe (PO ) F , (CH NH ) , H O
6.2(3) ꢃ
ꢂ
ꢄ ꢂ ꢃ
ꢂ
ꢂ ꢃ
ꢃ
Fe(OH)(H O)(O P}(CH ) }CO H) 6.3(2) ꢃ
ꢃ
ꢂ
ꢃ ꢃ
ꢃ
C}Fe(PO )
6.1 ꢃ
ꢂ ꢂ
(b)Neutron Di wraction Study
Fe (P O )
ꢃ ꢇ ꢂ
6.14 ꢃ
6.08 ꢃ
ꢄ
The patterns recorded and the calculated di!raction pro-
"les at 105 and 2 K are shown in Figs. 6a and 6b.
FeP SiO
ꢀꢀ
ꢂ
FIG. 6. Observed and calculated neutron powder di!raction pro"le of Fe P SiOꢀꢆ: (a) at ¹"105 K, (b) at ¹"2 K, and (c) di!erence between the
ꢂ ꢅ
observed spectra collected at 105 and 2K.

STRUCTURE AND PROPERTIES OF Fe P SiO
ꢂ ꢅ ꢀꢆ
77
Fe2
Fe1
Fe2
Fe1
(a)
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
-
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
+
c
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
a
b
Fe2
Fe2
Fe1
Fe2
Fe2
(b)
Fe2
Fe1
Fe2 Fe1
Fe1
Fe2
Fe1
Fe2
Fe2
Fe1
Fe2
Fe2
Fe1
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
Fe2
Fe1
c
Fe1
Fe2
Fe1
Fe2
a
b
Fe1
Fe2
Fe1
Fe1
Fe1
FIG. 7. Collinear arrangement of spin for antiferromagnetic ordering of Fe P SiO . The gray and white circles indicate opposing spin direction in
ꢂ ꢅ ꢀꢆ
s
intradimer [Fe O ] distance. The white bonds represent the 4.41, 4.85, 4.87, and 4.93 A interdimer
the ab plane. The gray bonds represent the 3.019 A
Fe O ] distances. (a) Projection along [110]. (b) Clinographic view.
s
ꢃ
ꢆ
[
ꢃ
ꢆ
At 2 K, additional lines, characteristic of an antiferromag-
It should be noted that a full re"nement is not possible
netic ordering, appear in agreement with the magnetic due to the lack of experimental information, as there are 61
measurements. All of the observed re#ections can be in- variable parameters to determine from 60 independent neu-
dexed in the same crystal unit cell and it was quickly tron data. Therefore, using the set of nuclear parameters
established that additional peaks 00l only occur with de"ned during the single-crystal X-ray study (Table 2) only,
l"2n#1 (forbidden by the 6 axis (Fig. 6)). The (001) line the scale factor, the lattice and half-width parameters, and
ꢂ
appears essentially as the strongest one; this implies that the the magnetic moment components (constrained to be equal
easy magnetization axis probably lies in this plane or in its for the two independent iron sites) were re"ned. The best "t
close neighborhood.
to the data is characterized by the standard quantities,
As shown in the previous section, there are two in-
dependent iron sites (Table 2) which give two magnetic Fe magnetic moment equal to 4.56(5) ꢃ . This value is
sublattices, and for each there are six crystallographically expected for a high-spin iron(III). The "nal re"nement and
R
"7.9% and R "5.6%, and gives the value of
,
3! +ꢊ%
equivalent positions per unit cell. The loss of the 6 axis the di!erence spectra between 105 and 2 K are shown in
ꢂ
leads to an antiferromagnetic arrangement in each Fe sub- Figs. 6b and 6c.
lattice.
All these structural and magnetic considerations suggest
an antiferromagnetic structure based on an antiferromag-
(c)Mo( ssbauer Study
netic arrangement in each [Fe O ] unit, with the spin
direction perpendicular to the [001] direction. The mag- at 295 K is shown in Fig. 8a. The width of each peak is
Paramagnetic state (¹'35 K). The observed spectrum
ꢃ ꢆ
netic structure is illustrated in Figs. 7a and 7b.
0.35 mm/s. This value is too great to represent the resonance

7
8
ELBOUAANANI ET AL.
TABLE 5
MoK ssbauer Spectral Parameters for Fe P SiO at 6 K
1
00
3
5
19
9
9
8
7
6
5
Site
ꢆ? (mm.s\ꢀ) 2ꢉ (mm.s\ꢀ)
H (T)
ꢈ (mm.s\ꢀ)
I (%)
1
2
0.540
0.558
0.096
!0.216
54.7
54.6
0.27
0.27
50
50
9
9
9
9
?
Relative to room temperature ꢁ-iron foil. ꢆ$0.005, 2ꢉ$0.005,
(
a) T = 295 K
H$0.1.
O3
O5
P3
-
2
-1
0
1
2
O8
Fe2
+
O6
Velocity mm/s
O9
O5
O3
O12
Fe1
+
P3
O4
Fe2
-
100
O9
Fe1
O3
9
8
6
4
2
0
8
6
O1
-
O10
O5
(
a)
P3
9
9
9
9
8
8
O8
Fe2
+
O6
O9
O5
O3
P3
O9
Fe1
+
Fe2
O4
-
Fe1
(
b) T = 6 K
O3
P3
O1
O10
O8
-
c
O5
Fe2
+
O6
O9
O5
-
10 -8 -6 -4 -2
0
2
4
6
8
10
a
b
O3
P3
Fe1
+
Velocity mm/s
O4
FIG. 8. Mo
K
ssbauer spectra of Fe P SiOꢀꢆat (a) ¹"295 K and ¹"6K.
O9
ꢂ ꢅ
of one type of iron but is consistent with the resonance of
two types. The spectrum was then accurately "tted with two
Lorentz-type quadrupole doublets where the intensity of
each doublet was constrained to be equal and the widths of
the peaks were "xed to 0.27 mm/s. Each doublet is asso-
ciated with each of the two crystallographically distinct iron
sites.
The calculated spectral parameters are presented in
Table 4.
The isomer shift values (ꢆ"0.431 and 0.435 mm/s) are
clearly characteristic of the paramagnetic high-spin iron(III)
O3
O9
O5 P3
O8
O6
+
O3
O9
O5
O3
O9
+
P3 O5
O4
-
O10
-
O3
P3
O1
(b)
O8
O9
O6
+
+
P3 O5
O4
(21). These high values are not unexpected: they are similar
to those found in Fe (P O ) (0.41 to 0.42 mm/s) (12) and it
-
O10
ꢄ
ꢃ ꢇ ꢂ
-
O3
P3
O1
has been well established (22) that, thanks to the inductive
c
O5
O3
O8
O9
O6
+
a
b
+
TABLE 4
P3
O5
O4
M oK ssbauer Spectral Parameters for Fe P SiO at 110 K
3 5 19
O9
Site
ꢆ? (mm.s\ꢀ) ꢇ (mm.s\ꢀ) ꢈ (mm.s\ꢀ)
I (%)
FIG. 9. Projection of the structure of Fe P SiO along [110] showing
ꢂ ꢅ ꢀꢆ
(a) the [Fe O ], PO connections and (b) exchange, superexchange, and
1
2
0.431
0.435
0.643
0.377
0.27
0.27
50
50
ꢃ
ꢆ
ꢄ
super-superexchange paths in Fe P SiO : intradimer [Fe O ], Fe}Fe
ꢂ ꢅ ꢀꢆ
and Fe}O}Fe; interdimer [Fe O ] via the P(3)O tetrahedra,
ꢃ
ꢆ
ꢃ
ꢆ
ꢄ
?
Relative to room temperature ꢁ-iron foil ꢆ$0.005, ꢇ$0.005.
Fe}O}P}O}Fe.

STRUCTURE AND PROPERTIES OF Fe P SiO
79
ꢂ ꢅ
ꢀꢆ
TABLE 6
Magnetic Interactions in Fe P SiO
3
5
19
Pathway
(A, 3)
Fe}Fe
Distance (A
Interaction
Nature
Sign
AF
n
s
s
)
Feꢂ>(1)}Feꢂ>(2)
Feꢂ>(1)}O(5)}Feꢂ>(2)
Feꢂ>(1)}O(2)} Feꢂ>(2)
Feꢂ>(1)}O(4)}Feꢂ>(2)
Direct
1
3.019
Superexchange
AF
AF
AF
1
1
1
4.23, 91
4.22, 92
4.21, 92
3.019
3.019
3.019
Feꢂ>(1)}O(6)}P(1)}O(1)}Feꢂ>(2)
Feꢂ>(2)}O(1)}P(1)}O(4)}Feꢂ>(1)
Feꢂ>(2)}O(1)}P(1)}O(4)}Feꢂ>(2)
Feꢂ>(1)}O(6)}P(1)}O(4)}Feꢂ>(2)
Feꢂ>(1)}O(6)}P(1)}O(4)}Feꢂ>(1)
Feꢂ>(1)}O(8)}P(2)}O(10)} Feꢂ>(2)
Feꢂ>(1)}O(8)}P(2)}O(2)}Feꢂ>(2)
Feꢂ>(1)}O(8)}P(2)}O(2)}Feꢂ>(1)
Feꢂ>(2)}O(10)}P(2)}O(2)}Feꢂ>(1)
Feꢂ>(2)}O(10)}P(2)}O(2)}Feꢂ>(2)
Feꢂ>(1)}O(9)}P(3)}O(3)}Feꢂ>(2)
Feꢂ>(2)}O(3)}P(3)}O(5)}Feꢂ>(1)
Feꢂ>(2)}O(3)}P(3)}O(5)}Feꢂ>(2)
Feꢂ>(1)}O(9)}P(3)}O(5)}Feꢂ>(2)
Feꢂ>(1)}O(9)}P(3)}O(5)}Feꢂ>(1)
Super-superexchange
AF
F
AF
F
AF
AF
F
AF
F
AF
AF
F
AF
F
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
6.91, 116
7.05, 111
7.02, 111
7.15, 114
7.18, 114
6.84, 115
7.08, 114
7.08, 114
7.08, 110
7.08, 110
6.83, 116
7.00, 106
7.10, 106
7.14, 116
7.04, 116
4.41
4.87
6.08
4.85
6.08
4.41
4.87
6.08
4.85
6.08
4.41
4.93
6.14
4.93
6.14
AF
Note. AF, antiferromagnetic; F, ferromagnetic; n, number of interactions per dimer; pathway, distance (Fe}O}P}O}Fe) in angstroms and angle on
oxygen or phosphorus in degrees; O(4), O(2), and O(5) are the oxygen atoms of shared faces.
e!ect, the ionicity of the Fe}O bonds in phosphates is rather are linked to each other through several exchange path-
high.
The two di!erent quadrupole splitting values (ꢇ"0.377
and 0.643 mm/s) indicate that the environment around one tions in the Fe P SiO compound: intra- and interdimer
ways.
It is clear that we have to consider many types of interac-
ꢂ ꢅ
ꢀꢆ
iron is more distorted than the other one. This di!erence [Fe O ]. These magnetic interactions are given in Table 6
ꢃ ꢆ
is also measured by the calculated distortion indices, and are described by the relevant parameters.
Dis"ꢁꢈ ((Fe}O) !Fe}O)ꢃ/6(Fe}O)ꢃ, of each iron co-
Gꢋꢀ
G
ordination polyhedron which are not the same for Fe(1) and
Intradimer Interactions
. The cation}cation direct interactions are important
since the cations separation is relatively small through the
). These interac-
tions, occurring between two 3d half-"lled orbitals, are obvi-
ously antiferromagnetic, as the transferred electron must be
antiparallel to the net spin at both ions (Goodenough rules
Fe(2): 10ꢄDis
"12 and 10ꢄDis
"42. Since the Fe(2)
$ꢈꢌꢀꢍ
$ꢈꢌꢃꢍ
1
octahedral coordination is the more irregular geometry, the
doublet ꢇ"0.643 mm/s should be assigned to Fe(2).
common face (distance Fe}Fe"3.019 A
s
Ordered state. The calculated and observed spectra at
K are shown in Fig. 8b. In the data analysis, two magnetic
sextets of equal area, one for each crystallographic site, and
with width of peaks "xed to 0.27 mm/s, were "tted to the
observed spectrum. The relative areas of the lines in each of
the two sextets were constrained to be in the ratio
6
(23)).
2
. The cation}anion}cation interactions are characterized
by the angles Fe}O}Fe near 903 (Table 6); accordingly they
are moderately antiferromagnetic, thanks to delocalization
superexchange, and partly to correlation superexchange
3
:2:1:1:2:3 as is required for an unoriented powder sample.
The hyper"ne spectral parameters are reported in Table 5.
The two internal hyper"ne "elds are similar, H"55 T,
(Goodenough rules (23)).
typical of high-spin iron(III) nearly at the saturation state,
in agreement with the neutron di!raction study.
Interdimer Interactions
DISCUSSION
There are several Fe}O}P}O}Fe paths connecting each
[
Fe O ] to its neighbors. As reported in the crystallo-
ꢃ ꢆ
We see in Figs. 9a and 9b that the antiferromagnetic graphic study, the [Fe O ] units form in"nite rows, parallel
dimers of the [Fe O ] face-sharing octahedra units to the c axis, connected to each other by PO tetrahedra
ꢃ ꢆ
ꢃ ꢆ
ꢄ

8
0
ELBOUAANANI ET AL.
(
Fig. 9a). The iron atoms in each row are linked to each
3. A. Leclaire, H. Chahboun, D. Groult, and B. Raveau, J. Solid State
Chem. 65, 168(19 86 ).
other through three Fe}O}P}O}Fe pathways, like
Fe}O(3)}P}O(9)}Fe (Fig. 9b and Table 6), which are anti-
ferromagnetic. These AF interdimer interactions are prob-
ably weaker than the AF direct intradimer interactions and
are called super-superexchange type.
4
. S. L. Wang, C. C. Wang, and K. H. Lii, J. Solid State Chem. 74,
09 (1988).
4
5
6
. H. M. Rietveld, J. Appl. Crystallogr. 2, 65 (1969).
. J. Rodriguez-Carvajal, Fullprof Program, Laboratoire Leon Brillouin,
1998.
7
8
. G. Le Caer, private communication.
. G. Sheldrick, Shelxs 97 and Shelxl 97, Programs for the Re"nement of
The [Fe O ] units in adjacent rows are also linked by
ꢃ ꢆ
PO tetrahedra (Fig. 9a) and the magnetic interactions
between them are also assured by super-superexchange
ꢄ
Crystal structure, Univ. GoK ttingen, Germany, 1997.
9
. R. H. Blessing, Crystallogr. Rev. 1, 3 (1987).
Fe}O}P}O}Fe. We see in Fig. 9b that two superexchange
pathways which go through each O(5) atom are respectively
ferro- and antiferromagnetic. The geometric characteristics
of these pathways being almost the same (Table 6), there is,
in this case, a frustration phenomenon. There is the same
frustrated magnetic super-superexchange phenomenon for
1
0. J. A. Ibers and W. C. Hamilton, &&International Tables for X-Ray
Crystallography,'' Vol. 4. Kynoch, Birmingham, 1976.
1. I. D. Brown and D. Altermatt, Acta Crystallogr. B 41, 244 (1985).
1
1
2. L. K. Elbouaanani, B. Malaman, and R. G eH rardin, J. Solid State Chem.,
submitted.
1
3. M. Ijjaali, B. Malaman, C. Gleitzer, and M. Pichavant, Eur. J. Solid
Inorg. Chem. 26, 73 (1989).
all the pathways which go through the oxygen atoms be- 14. D. Corbridge, Bull. Soc. Fr. Miner. Crist. 94, 271 (1971).
1
1
1
1
1
2
2
5. A. Leclaire, J. C. Monier, and B. Raveau, Acta Crystallogr. B 40, 180
1984).
6. A. Leclaire, M. M. Borel, A. Grandin, and B. Raveau, Mater. Chem.
Phys. 12, 537 (1985).
7. A. Leclaire, M. Lamire, and B. Raveau, Acta Crystallogr. C 44, 1181
(1988).
8. M. Cavellec, C. Egger, F. Linares, M. Nogues, F. Varret, and
G. Ferey, J. Solid State Chem. 134, 349 (1997).
longing to the common faces of the [Fe O ] units: O(2),
O(4), and O(5) (Table 6). It will be interesting to propose
a theoretical model to explain these results.
ꢃ ꢆ
(
ACKNOWLEDGMENTS
We are grateful to the Institut Laue Langevin (Grenoble) for the provis-
ion of neutron facilities.
9. M. Riou-Cavellec, M. Sanselme, J. M. Grene
`
che, and G. Ferey, Solid
State Sci. 2, 717 (2000).
0. L. K. Elbouaanani, B. Malaman, and R. Ge
48, 455 (1999).
1. F. Menil, J. Phys. Chem. Solids 46, 763 (1985).
H
rardin, J. Solid State Chem.
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1
1
. L. K. Elbouaanani, B. Malaman, and R. Ge
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. R. Glaum and A. Schmidt, Acta Cryst. C 52, 762 (1996).
H
rardin, J. Solid State
22. C. Gleitzer, Eur. J. Solid Inorg. Chem. 28, 77 (1991).
23. J. B. Goodenough, &&Magnetism and the Chemical Bond.'' Interscience
Publishers, New York, 1966.
2