Ba2PO4I, Sr2PO4I, and Pb2PO4I - A new structure type and three of its representatives

Article abstract of DOI:10.1002/zaac.201400221

The compound Pb₂PO₄I was synthesized via a solid state reaction under inert conditions. None of the known structure types of other compounds of the type M₂(P,V,As,Cr)O₄(F,Cl,Br,I) provided a similar pattern. Structure solution was carried out by evaluation of an X-ray diffractogram of polycrystalline powder using the methods simulated annealing and difference Fourier. Pb₂PO₄I crystallizes in the/space group P2₁/c with the lattice parameters a = 9.0451(1) ?, b = 8.7593(1) ?, c = 8.5740(1) ?, and β = 111.128(1)° . The isotypic compounds Sr₂PO₄I and Ba₂PO₄I were synthesized, too. Their crystallographic structure was refined by Rietveld analysis. The structure of the three compounds is described and discussed.

Full text of DOI:10.1002/zaac.201400221

ARTICLE
DOI: 10.1002/zaac.201400221
Ba2PO4I, Sr2PO4I, and Pb2PO4I – A New Structure Type and Three of Its
Representatives
Robert Haberkorn,*[a] Jessica Bauer,[a] and Guido Kickelbick[a]
Keywords: X-ray diffraction; Structure determination; Rietveld analysis; Lead
Abstract. The compound Pb2PO4I was synthesized via a solid state space group P21/c with the lattice parameters a = 9.0451(1) Å, b =
reaction under inert conditions. None of the known structure types of 8.7593(1) Å, c = 8.5740(1) Å, and β = 111.128(1)°. The isotypic com-
other compounds of the type M2(P,V,As,Cr)O4(F,Cl,Br,I) provided a
similar pattern. Structure solution was carried out by evaluation of
pounds Sr2PO4I and Ba2PO4I were synthesized, too. Their crystallo-
graphic structure was refined by Rietveld analysis. The structure of the
an X-ray diffractogram of polycrystalline powder using the methods three compounds is described and discussed.
simulated annealing and difference Fourier. Pb2PO4I crystallizes in the
Sr2VO4I, Sr2AsO4I,[7] Mn2PO4F, and Mn2PO4Cl,[8] but did not
publish detailed crystallographic information.
Introduction
Within the systems MII3(AVO4)2-MIIX2 (A = P, V, As, Cr;
X = F, Cl, Br, I) many compounds of the general formula
MII5(AVO4)3X or M2AO4X may be found and will be mentioned
in this work as apatite-MF or spodiosite-MF respectively. The
apatite-MF compounds show similar structures and belong to
the apatite family. Most of them crystallize in the space group
Meanwhile six different structure types of spodiosite-MF
compounds are known. These types are listed in Table 1 and
some sources of crystallographic information on representa-
tives of these types are given in Table 2. The chlorspodiosite
Table 1. Structure types of compounds M2AO4X.
¯
P63/m or a subgroup of this space group (P63, P21/b, P1).
Many representatives of the spodiosite-MF ones belong to the Type
Mineral
Space group
Z
spodiosite family and crystallize in the space group Pbcm (Z
= 4) or a subgroup thereof (I2/c, P21/a). Other structure types
of spodiosite-MF are also known. Frequently scientists used to
call spodiosite-MF compounds either spodiosite or wagnerite,
independently of the structure present.[1,2]
In the 19th century several authors[3–5] have already claimed
to have synthesized “wagnerites” of the general formula
M2AO4X. Ditte reported the preparation of the compound
Pb2PO4I in 1886 [4]. Of course characterization by X-ray dif-
fraction was not possible at that time. The shape of the crystals
and elemental analysis were used to substantiate the existence
of the reported composition and relationship to minerals like
wagnerite.
Ca2PO4Cl
Mn2PO4F
Mg2PO4F
Mg2PO4Cl
Sn2PO4Cl
Cu2AsO4Cl
chlorspodiosite
triplite
wagnerite
Pbcm (57)
C2/c (15)
P21/a (14)
Pna21 (33)
Ama2 (40)
P21/m (11)
4
8
16
4
4
2
Table 2. Literature providing crystallographic information on some
compounds M2AO4X.
Type
Formula
Without atomic Including
positions
atomic positions
Ca2PO4Cl
Ca2PO4Cl
Ca2VO4Cl
Ca2AsO4Cl
Ca2CrO4Cl
Sr2VO4Cl
Sr2VO4Br
Sr2CrO4Cl
(Mn,Fe)2PO4F
Mn2PO4F
Cu2PO4F
Fe2PO4Cl
Mg2PO4F
Mg2PO4Cl
Mn2PO4Cl
Sn2PO4Cl
Cu2AsO4Cl
Co2AsO4Cl
[17]
[18]
[18]
[2]
[19]
[19]
[2]
In the 20th century other scientists reported the synthesis
of several spodiosite-MF compounds: Ca2PO4Cl,[6] Ba2VO4Br,
Ba2PO4I, Ba2AsO4I, Ba2VO4I,[1] Mn2PO4Cl, Mn2PO4Br,
Co2PO4Cl, Mg2PO4Cl, Mg2AsO4Cl, Ca2VO4I, Ca2AsO4I,
[10, 20]
[10]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[16]
[28]
[28]
Mn2PO4F
* Dr. R. Haberkorn
Fax: +49-681-302-70652
E-Mail: haberkorn@mx.uni-saarland.de
[a] Anorganische Festkörperchemie
Universität des Saarlandes
Mg2PO4F
Mg2PO4Cl
Box 151150
66041 Saarbrücken, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201400221 or from the au-
thor.
Sn2PO4Cl
Cu2AsO4Cl
Z. Anorg. Allg. Chem. 2014, 640, (15), 3153–3158
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. Haberkorn, J. Bauer, G. Kickelbick
ARTICLE
type is the most common one, but especially small anions and of (100) and (001) texture and yielded Rwp = 0.064 (RBragg
=
cations tend to form special structures like triplite or wagnerite. 0.024). The atomic positions are listed in Table 3. The Rietveld
In the last three decades only few investigations on plot for the final refinement is displayed in Figure 1.
spodiosite-MF compounds have been carried out, but Chiu et
al.[9] report on Eu2+ doped Ca2PO4Cl showing blue lumines-
cence, which might be of interest for application in white light-
emitting diodes (wLEDs).
Results and Discussion
Although syntheses of Pb2PO4I[4] and Ba2PO4I[1] are re-
ported in literature no information about the spodiosite-MF
structure type is given. Sr2PO4I, to the best of our knowledge,
has never been reported before.
The scan of Pb2PO4I does not show a pattern similar to
any known spodiosite type compound such as Ca2PO4Cl or
Sr2VO4Br. Within the 2θ range from 7 to 72° of the Pb2PO4I
diffractogram the intensities and positions of 146 peaks could
be extracted. The peak positions could be indexed on the basis
of a monoclinic cell with a = 9.045 Å, b = 8.761 Å, c =
8.575 Å, and β = 111.13° (final values are given in Table 4).
Figure 1. Rietveld plot of the XRD pattern of Pb2PO4I, with observed
full scan and zoomed region. Refined intensity (light gray), measured
Based on these metric conditions the pattern was checked for
systematic extinctions and possible space groups. The space
group P21/c proofed to be the most reliable one and was se-
lected for structure solution.
intensity (black), difference plot, and markers for Pb2PO4I.
The Rietveld refinement did not show additional peaks be-
side those of Pb2PO4I or any other significant misfit indicating
The volume V of the unit cell found by indexing was the existence of another phase. Pb2PO4I was yielded as a pure
634 Å3. The spodiosite type compound Sr2VO4Br has a unit phase, although an excess of 5% PbI2 was used. The silica
cell volume V = 566 Å3.[10] According to Shannon[11] the ionic tube, which was used for synthesis, showed a thin orange layer
radius of I (rI–1 [6]= 2.20 Å) is much larger than the radius of at the complete surface, probably mainly consisting of PbI2. It
Br (rBr–1 [6]= 1.96 Å). From this an additional volume of about may be assumed all the excessive PbI2 condensed via sublima-
18 Å3 per atom I instead of Br may be estimated. The ex- tion at the wall of the tube.
change of the other atoms is of minor influence. Therefore Z
= 4 was estimated for this cell, which corresponds to 32 atoms ilar ionic radius as Sr2+ (rSr+2 [6]= 1.18 Å). Both are relatively
within the unit cell.
large cations and Ba2+ (rBa+2 [6]= 1.35 Å) is a large cation, too.
According to Shannon[11] Pb2+ (rPb+2 [6]= 1.19 Å) has a sim-
The structure solution was started by simulated annealing. Therefore Sr2+ and Ba2+ were promising candidates to replace
Eight sites were provided, each at (0.01, 0.01, 0.01) as starting Pb2+ in this structure. Indeed, the compounds Sr2PO4I and
position. Since the general position of P21/c has a multiplicity Ba2PO4I could be synthesized, showing a pattern similar to
of four this gives 32 atoms as long as no special position is that of Pb2PO4I (Figure 2).
occupied. However the result was not satisfying. Therefore the
The first XRD measurements on Sr2PO4I showed a fast de-
search was limited to three sites according to eight atoms Pb composition of the sample when exposed to air. Therefore sub-
and four atoms I. After simulated annealing the three positions sequently this compound was not prepared into a standard
were used for a Rietveld refinement and yielded a relatively sample holder for X-ray diffraction, but in the glove box into
proper fit with Rwp = 0.149 (RBragg = 0.090). The remaining a sample holder protecting against contact to air. The sample
positions were determined by difference Fourier. Within the was mixed with Apiezon grease and enclosed between Mylar
next step only the P1 site was searched for and then the four foils, which were fixed by two concentrical rings (supplier of
O sites. The final Rietveld refinement allowed a combination the sample holder: PANalytical B.V., The Netherlands). Imme-
Table 3. Site parameters for Pb2PO4I, space group P21/c. All sites have the Wyckoff position 4e.
Site
x
y
z
B /Å2
Pb1
Pb2
I
0.1594(1)
0.7319(1)
0.5026(3)
0.9640(8)
0.1487(14)
0.0943(15)
0.1354(13)
0.9027(15)
0.3000(2)
0.3264(2)
0.9375(3)
0.0471(8)
0.0781(17)
0.1234(15)
0.6673(17)
0.4233(17)
0.5498(2)
0.0286(2)
0.2439(3)
0.2715(10)
0.3590(19)
0.7214(19)
0.1616(17)
0.5701(19)
1.61(3)
1.46(3)
2.05(5)
0.56(15)
0.85(17)
0.85
P
O1
O2
O3
O4
0.85
0.85
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Ba2PO4I, Sr2PO4I, and Pb2PO4I
Table 4. Lattice parameters and additional data about the scan and the
Rietveld refinements.
Parameter
Ba2PO4I
Pb2PO4I
Sr2PO4I
2θ range/°
7–120
7–120
8–80
a /Å
b /Å
c /Å
9.3645(1)
9.2418(1)
8.8606(1)
9.0451(1)
8.7593(1)
8.5740(1)
9.1137(2)
8.9049(2)
8.4339(2)
β /°
111.377(1) 111.128(1) 112.212(1)
V /Å3
714.08(1)
4
633.64(1)
4
633.67(2)
4
Z
ρ(X-ray) /g·cm–3
Rwp
4.619
0.053
0.022
100
6.670
0.064
0.024
100
4.163
0.029
0.007
90.6(2)
69
RBragg
Weight fraction /%
No. of refined parameters
57
56
Figure 2. Main part of the XRD pattern of Ba2PO4I, Pb2PO4I, and
Sr2PO4I.
water to become SrI2·2H2O, but did not show the peaks of the
decomposition phase, even after a few hours. When removing
the protective dome shield SrI2·6H2O was formed from the
other hydrates of SrI2, followed by decomposition of Sr2PO4I,
which was completed after a few hours. Another sample with
excess of Sr3(PO4)2 did not show SrI2 or any hydrate thereof,
but the same decomposition of Sr2PO4I in air within several
hours. The product of the decomposition is SrI2·6H2O and at
least one additional phase, which could not be identified yet.
The atomic positions of Pb2PO4I could be used as starting
values for the Rietveld refinement of the diffractograms of
Sr2PO4I and Ba2PO4I. The quality of the fits proved all three
compounds to be isotypic. The lattice parameters and the resid-
ual values of these refinements are given in Table 4, the atomic
positions in Table 5 and Table 6. Due to the higher background
radiation for Sr2PO4I the Rwp is lower than for the other scans.
Due to the more broadened peaks also the fit of the peaks is
better (small RBragg), nevertheless the quality of many of the
refined parameters is lower. The quantitative phase analysis
gave strontium phosphate and 4 wt-% of hydrates of strontium
diately after locking out several XRD measurements each with
20 min scan time were started. The second diffractogram
showed already peaks of the decomposition phase. When pre-
pared in a dome construct (Figure 3) (supplier: Bruker AXS
GmbH, Germany) inside the glove box SrI2·H2O was found as
the first iodine rich phase, which slowly took up additional
Figure 3. Photographs of sample holders for inert atmosphere: (a)
sample holder with foils, (b) sample holder with dome (closed), (c)
mounting tool for sample holder with dome, (d) sample holder with
dome (opened).
Table 5. Atomic parameters for Ba2PO4I, space group P21/c.
Site
x
y
z
B /Å2
Ba1
Ba2
I
0.1617(1)
0.7493(1)
0.5044(1)
0.9617(5)
0.1437(9)
0.0746(9)
0.1232(9)
0.8941(9)
0.3083(2)
0.3271(1)
0.9234(2)
0.0539(6)
0.0917(12)
0.1007(11)
0.6711(13)
0.4179(12)
0.5409(2)
0.0482(2)
0.2426(2)
0.2610(7)
0.3436(12)
0.7067(13)
0.1712(12)
0.5649(11)
1.11(3)
1.17(3)
1.66(3)
1.24(11)
1.40(12)
1.40
P
O1
O2
O3
O4
1.40
1.40
Table 6. Atomic parameters for Sr2PO4I, space group P21/c.
Site
x
y
z
B /Å2
Sr1
Sr2
I
0.1496(3)
0.7536(3)
0.5068(3)
0.9524(10)
0.1431(16)
0.0718(15)
0.1353(16)
0.8945(15)
0.3050(3)
0.3286(3)
0.9040(2)
0.0544(8)
0.0837(18)
0.1164(15)
0.6690(16)
0.4170(16)
0.5406(3)
0.0488(3)
0.2562(3)
0.2569(12)
0.3434(18)
0.7129(17)
0.1681(16)
0.5542(17)
1.79(9)
1.69(8)
2.80(7)
1.23(25)
1.42(21)
1.42
P
O1
O2
O3
O4
1.42
1.42
Z. Anorg. Allg. Chem. 2014, 3153–3158
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R. Haberkorn, J. Bauer, G. Kickelbick
ARTICLE
Table 7. Distances d of atoms, average distances ϽdϾ, and coordination numbers cn.
Site
Parameter
Ba2PO4I
Pb2PO4I
Sr2PO4I
M1
cn
7ϫO + 2ϫI
2.62–2.93
2.790
3.70–3.93
3.815
5ϫO + 3ϫI
2.62–2.93
2.719
3.62–3.66
3.635
7ϫO + 2ϫI
2.35–2.89
2.660
3.59–3.74
3.665
4ϫO + 3ϫI
2.35–2.85
2.578
3.31–3.50
3.409
7ϫO + 2ϫI
2.49–2.80
2.636
3.50–4.02
3.752
5ϫO + 3ϫI
2.40–2.74
2.560
3.43–3.55
3.477
d(M1–O) /Å
Ͻd(M1–O)Ͼ /Å
d(M1–I) /Å
Ͻd(M1–I)Ͼ /Å
cn
d(M2–O) /Å
Ͻd(M2–O)Ͼ /Å
d(M2–I) /Å
Ͻd(M2–I)Ͼ /Å
cn
M2
P
I
4
4
4
d(P–O) /Å
Ͻd(P–O)Ͼ /Å
cn
1.52–1.64
1.593
5ϫBa
1.59–1.63
1.608
5ϫPb
1.57–1.63
1.595
5ϫSr
d(I–M)
Ͻd(I–M)Ͼ /Å
3.62–3.93
3.707
3.31–3.74
3.511
3.43–402
3.587
iodide beside 91 wt-% of the target phase within the sample of
Sr2PO4I.
Note that the following discussion covers all three structures
if not a single one is explicitly mentioned. The P atom is coor-
dinated by four oxygen atoms forming a slightly distorted tet-
rahedron. According to the Rietveld refinements the distances
between P and O are all within the range 1.52–1.64 Å (Table 7)
and all angles O–P–O within the range 101–117°. Due to the
uncertainty of data derived from powder pattern the distortion
of the tetrahedra is possibly smaller than implied by the above
mentioned values. The mean values ϽdϾ of distances d are
more reliable than single values.
The cation M1 is ninefold coordinated by seven O and two
I atoms, whereas M2 is eightfold coordinated by five O (except
Pb2; cf. Table 7) and three I atoms. In accordance with the
lower number of coordinating oxygen atoms the mean dis-
tances Ͻd(M–O)Ͼ are smaller for M2 than for M1. These
mean values are also smaller than the sum of the ionic radii,
Figure 4. 2ϫ2 unit cells of the structure of Ba2PO4I projected along
suggesting a strong coordinative bonding between M and O. the b axis. Coordination spheres of distorted tetrahedra of O around P.
In reverse, the mean distances Ͻd(M–I)Ͼ are nearly all longer
than the sum of the radii and only Ͻd(Pb2–I)Ͼ is smaller than
this sum. In addition Ͻd(Pb1–I)Ͼ is smaller than the other
Ͻd(M1–I)Ͼ values. The higher polarizability of Pb seems to
enable a stronger, probably more covalent bonding with the
polarizable I than the less polarizable Ba or Sr.
The sequence of “layers” M–O–P–O–M may be regarded as
a slab of metalphosphates, fixed by strong coordinative bond-
ing and electrostatic forces. Thus the structure may be de-
scribed as stacking of metalphosphate slabs and iodine layers.
The iodine atoms form a nearly plane layer, which shows
distorted hexagonal symmetry and contains as many atoms as
the P “layer”. It is a pseudohexagonal packed layer of iodine
(Figure 5). Because of the large distances between the P atoms,
the I atoms have large distances, too. To enable a relatively
dense packing of the atoms within this iodine layer these atoms
must be very large to fill this layer. The distance between an I
atom and the six neighboring I atoms is 4.50–5.47 Å for
This structure type shows elements of a layered structure
(Figure 4). Along the a axis the sequence of “layers” is
P–O–M–I–M–O,P–O…. The PO4 tetrahedra are isolated, nei-
ther sharing an edge nor a corner with another PO4 tetrahedron.
Neglecting the coordinating I, the M1 and M2 sites are coordi-
nated by seven (M1) or five (M2) oxygen atoms forming a
dome like partial shell. The M1 and M2 sites are located above
or below the O–P–O arrangement and outside the “dome” of
coordinating oxygen atoms. These M1–O7 and M2–O5 polyhe-
dra share corners and edges with the PO4 tetrahedra, resulting
in large distances between the tetrahedra and the phosphorus
atoms inside.
Ba2PO4I, more than twice the radius of iodine (rI–1
=
[6]
2.20 Å). Even iodine, the biggest halide, is too small for a
dense packing of this layer.
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Ba2PO4I, Sr2PO4I, and Pb2PO4I
for Sr2PO4I). The structure of Sn2PO4Cl does not show a lay-
ered character, but is a coordination structure.
Each Sn atom is coordinated by four O and three Cl atoms
similar to the Ba1–O7/I2 and Ba2–O5/I3 polyhedra. But the
distance between the “layers” of Sn above and below the chlo-
rine “layer” (about 3.1 Å) is much smaller than the correspond-
ing distance (about 4.9 Å) for Ba2PO4I. The PO4 tetrahedra
within a slab of metalphosphates are all orientated in the same
direction for Sn2PO4Cl, and the crystal system is orthorhombic
(space group Ama2) instead of monoclinic. The space group
P21/c is no subgroup of the space group Ama2, but both share
the same subgroup P21. From a topological view the a and c
axes of Sn2PO4Cl have double respectively half the length of
the corresponding axes of Ba2PO4I. A more detailed compari-
son of all the structure types mentioned above will be given
elsewhere.
In an inert atmosphere all three compounds M2PO4I men-
tioned above may be stored for several months without signifi-
cant decomposition. Sr2PO4I is less stable than both the other
compounds when exposed to air. Due to the lower stability of
the Sr compound, when exposed to air and the special behavior
of the ns2 cation Pb2+ this new structure type should be named
after Ba2PO4I as the “normal” representative of this type.
Figure 5. 2ϫ2 unit cells of the structure of Ba2PO4I projected along
the a axis. All atoms besides I removed. Pseudohexagonal arrangement
of I atoms.
The corresponding I–I distances are within the range of
4.45–5.03 Å for Sr2PO4I (4.31–5.40 Å for Pb2PO4I) and pro-
vide a more dense layer. The Sr compound is less stable than
both of the other compounds. For even smaller cations than Sr
this structure probably will not exist. For smaller anions than
iodide it may be difficult to form dense layers due to the repul-
sion force of these anions.
The structure types chlorspodiosite, triplite, wagnerite, and
Mg2PO4Cl show channels filled with columns of anions X. The
structure of Cu2AsO4Cl does not include such channels.
The structure of Sn2PO4Cl, however, shows distorted
hexagonal “layers” of anions X and a stacking of slabs of
metalphosphates and these “layers” of chlorine, similar to the
Ba2PO4I structure. In Figure 6 the structure is displayed in a
similar manner as the structure of Ba2PO4I in Figure 4 and
Figure 5. In Sn2PO4Cl the hexagonal packing of the “layers”
of the halogen atoms is even less distorted than in Ba2PO4I,
but also less dense. The distances d(Cl–Cl) are within the
range 4.74–4.94 Å, much more than twice the radius of chlo-
rine (rCl–1 [6]= 1.81 Å). More exactly: the ratio Ͻd(X–X)Ͼ/
(2ϫrX) is 135% for Sn2PO4Cl and 112% for Ba2PO4I (106%
Conclusions
The compounds Ba2PO4I, Pb2PO4I, and Sr2PO4I may be
synthesized by a solid state route in an inert atmosphere. The
synthesis of Ba2PO4I and Pb2PO4I was claimed in the 19th
century, whereas Sr2PO4I has never been mentioned before.
Therefore the three compounds may be called “new”.
The structure of Pb2PO4I could be determined by simulated
annealing and difference Fourier methods, followed by a Riet-
veld analysis. This is not only a new structure, but also a new
structure type with the monoclinic space group P21/c and four
formula units within the unit cell. The two other compounds
show the same structure type and their structures were refined
by Rietveld analysis, too. The Sr compound is less stable than
both the other representatives of this type, which should be
called Ba2PO4I type.
The structure is similar to a layered structure with stacking
of slabs of metalphosphates and layers of iodine in turn. A slab
consists in the inner part of distorted PO4 tetrahedra, connected
to another by dome-shaped M–O coordination polyhedra. This
structure type probably will only exist in the case of large, low
charged anions and large cations.
The structure of Sn2PO4Cl, space group Ama2, is related to
this new structure type, but is a coordination structure without
the character of a layered structure.
Experimental Section
The chemicals used were of the grade “pro analysi” or of a higher
grade. PbI2 was synthesized by precipitation from aqueous solutions
of Pb(NO3)2 and KI. BaI2·2H2O was dried in air at 150 °C overnight
to yield BaI2·H2O. Commercial SrI2 of 99.99% purity was used. The
phosphates were synthesized by calcination according to Equation (1):
Figure 6. 2ϫ2 unit cells of the structure of Sn2PO4Cl. Position of
sites taken from Ref. [16]. (a) Projection along the c axis. (b) All atoms
besides Cl removed, projection along the a axis.
Z. Anorg. Allg. Chem. 2014, 3153–3158
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R. Haberkorn, J. Bauer, G. Kickelbick
ARTICLE
3MCO3 + 2(NH4)2HPO4 Ǟ M3(PO4)2 + 4NH3Ȇ + 3CO2Ȇ + 3H2OȆ
to have only the Lorentian part of crystallite size as microstructural
(1) refinable and constraint to the same value for all peaks.
Further details of the crystal structures investigations may be
obtained from the Fachinformationszentrum Karlsruhe, 76344 Egg-
enstein-Leopoldshafen, Germany (Fax: +49-7247-808-666; E-Mail:
crysdata@fiz-karlsruhe.de, http://www.fiz-karlsruhe.de/request for de-
posited data.html) on quoting the depository numbers CSD-427715
(Ba2PO4I), CSD-427716 (Pb2PO4I), and CSD-427717 (Sr2PO4I).
The starting materials were ground in an agate mortar after adding n-
pentane. The dried mixture was calcinated in air, using platinum cruci-
bles and a muffle furnace at temperatures of 1100 °C [Sr3(PO4)2,
Ba3(PO4)2] or 700 °C [Pb3(PO4)2] analogous to syntheses described in
the literature.[12] The product was homogenized and fired repeatedly
at the same temperature until a pure phase was yielded. The iodophos-
phates were prepared according to Equation (2):
Supporting Information (see footnote on the first page of this article):
The Rietveld plots of the samples Ba2PO4I and Sr2PO4I are shown in
Figure S1 and Figure S2.
M3(PO4)2 + MI2 Ǟ 2M2PO4I
(2)
To compensate loss of MI2 by sublimation an excess of 5% was
weighed. Due to the hygroscopic behavior of SrI2 weighing for
Sr2PO4I was done in a glove box. The starting materials were ground
in an agate mortar and filled into a silica tube. To remove H2O in
BaI2·H2O the tube was heated in dynamic vacuum prior to sealing.
The temperature for drying was increased within several hours from
room temperature to a maximum of 400 °C. The sealed tube was posi-
tioned upright in a muffle furnace and heated to 600 °C (Pb2PO4I,
Sr2PO4I) or 750 °C (Ba2PO4I) for 6 h. After allowing to cool down to
room temperature the tubes were opened in air and prepared into a
standard sample holder for X-ray diffraction (Pb2PO4I, Ba2PO4I) or
were opened in a glove box and mounted into a sample holder protect-
ing against contact to air (Sr2PO4I) (Figure 3).
References
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X-ray scans were recorded with a D8 Advance diffractometer (supplier
Bruker AXS, Karlsruhe, Germany) with focusing Bragg-Brentano ge-
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7 to 120°. Usually the scan time was 2 h. Samples in protective sample
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before starting the scan with 2 h scan time and a 2θ range from 8 to
80°. No monochromator was attached, but low energy radiation was
removed by discriminating the detector to 8.0Ϯ1.5 keV and Cu-Kβ
radiation was reduced to 1% relative intensity by a Ni foil. A fast
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The program Topas was used to extract individual peak positions, to
index unknown patterns,[13] for structure solution by simulated anneal-
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width and shape of the peaks as well as correcting peak positions was
done according to the fundamental parameters approach,[15] as im-
plemented in Topas. The instrumental function was determined by a
scan of LaB6. For Rietveld analysis the following parameters were
refined: lattice parameters, sample height displacement, microstruc-
tural parameters, coordinates of the atomic sites, and individual iso-
tropic temperature parameters for most sites, but constraining the tem-
perature factor of oxygen sites to a single parameter. If a parameter
reached an upper or lower limit then this parameter was fixed for a
subsequent run. For extracting peak positions all peaks were constraint
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[22] J. R. Rea, E. Kostiner, Acta Crystallogr., Sect. B 1972, 28, 2525.
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Received: May 7, 2014
Published Online: November 17, 2014
3158
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Z. Anorg. Allg. Chem. 2014, 3153–3158