ARTICLE IN PRESS
V.V. Chernaya et al. / Journal of Solid State Chemistry 177 (2004) 2875–2880
2876
dramatically changes the structure resulting in layers of
square pyramids linked by PO groups [8,9].
structure investigations can be obtained from the
Fachinformationszentrum Karlsruhe, 76344 Eggen-
depository numbers CSD413693 and CSD413694.
Thermal analysis was performed on a NETZSCH
STA 449C instrument in a purified Ar flow.
4
Recently, we reported the synthesis and investigation
of the new vanadylvanadates Na MVO(VO ) (M=Sr,
2
4 2
Ca) [10]. This structure is somewhat similar to that of
Ba VO(PO ) and the A-cations are orderly situated
2
4 2
between the chains. Na SrVO(VO ) revealed a weak
2
4 2
antiferromagnetic transition at about 80 K resulting
4
Electron diffraction (ED) and high-resolution elec-
tron microscopy (HREM) were performed with a JEOL
4000EX microscope. The image simulations were made
using the MacTempas software.
Measurements of the ESR spectra have been per-
formed on a conventional cw ESR spectrometer
ADANI PS100.X at room temperature. Since all
investigated compounds are dielectric we used bulk
ceramic samples for ESR measurements.
Magnetic susceptibility measurements were per-
formed on a Quantum Design MPMS SQUID magnet-
ometer in the range between 2 and 400 K at fields of 0.1,
1 and 5 T.
+
from the superexchange interaction of the V
5
atoms
via V O groups. One may expect that compounds
+
4
5
+
with a similar structure may be formed during a V
5
-
+
P
substitution.
Below we present the results of the synthesis and
investigation of new complex vanadyl(IV)phosphates
Na MVO(PO ) (M=Ca, Sr) by means of X-ray
2
4 2
diffraction, electron microscopy, magnetic susceptibility
and ESR measurements.
2
. Experimental
Bulk samples of Na SrVO(PO ) and Na2CaVOðPO Þ
2
4 2
4 2
were obtained by heating stoichiometric mixtures of
Na P O , Sr P O or Ca P O and VO in an evacuated
3. Results and discussion
4
2
7
2
2
7
2
2
7
2
ꢀ
and sealed silica tube for 36 h at 700 C. Reagents were
thoroughly ground in an agate mortar under acetone,
pressed into pellets and placed into silica tubes. Na P O
2 7
3.1. Crystal structure
4
was obtained by heating Na HPO in dynamic vacuum at
7
The ab initio solution and following structure
refinement for Na SrVO(PO ) were carried out using
2
4
ꢀ
00 C for 24 h; M P O (M=Ca, Sr) were synthesized by
2 2 7
2
4 2
annealing a stoichiometric mixture of MCO3 and
ꢀ
the WinCSD program package [12]. The larger differ-
ence in Z-number for Sr and V atoms (in comparison
with that for Ca and V) allowed to distinguish uniquely
these atoms inside the unit cell during the model
NH H PO at 800 C for 48h in air.
4
2
4
The XRD patterns were indexed using the TREOR90
program [11]. Both Na CaVO(PO ) and Na SrVO
2
4 2
2
(
PO4)2 have an orthorhombic unit cell with
˚
construction. Since the reflections belonging to Na Sr
2
˚
lattice parameters a ¼ 10:5305ð3Þ A, b ¼ 6:5617ð2Þ A,
VO(PO ) mostly do not overlap with reflections of the
4
2
˚
˚
c ¼ 10:0595ð3Þ A
and
a ¼ 10:6435ð6Þ A,
˚
b ¼
unknown impurity, this phase was chosen for the
structure solution. Integral intensities were extracted
X
with the Win Pow program package [15] and used for
˚
6
:6194ð4ÞA, c ¼ 10:2483ð5Þ A for Ca and Sr, respec-
tively; Z ¼ 4: In the X-ray pattern of the Sr-containing
phase a few weak peaks were present (less than 5% of
intensity) of an unknown admixture and a change of
synthetic conditions did not result in the synthesis of a
pure product. The Ca-containing sample was obtained
as a single-phase material. We failed to obtain single
crystals of the materials because both compounds melt
the further structure calculations and refinements. The
Pnma space group was chosen according to the electron
diffraction data (see below). The coordinates of the
heavy atoms were found from direct methods. The
coordinates for the phosphorus and oxygen atoms were
extracted from Fourier and difference Fourier maps.
Finally, the Rietveld method refinement was used and
ranges containing admixture peaks were excluded from
the calculations. The thermal parameters for the oxygen
atoms were constrained. The atomic coordinates found
for Na SrVO(PO ) were taken as the initial ones for the
ꢀ
with decomposition (at 730 C for Na CaVO(PO ) and
2
4 2
ꢀ
at 800 C for Na SrVO(PO ) ) forming whitlockite-like
4 2
phases. Therefore the structure solution was done using
powder diffraction data.
X-ray powder diffraction (XPD) data for the struc-
ture solution and refinement were collected on a STOE
diffractometer (transmission diffraction geometry,
2
2
4 2
refinement of the Na CaVO(PO ) structure. The
2
4 2
experimental and structural parameters for Na MVO
2
CuK -radiation, Ge-monochromator, linear-PSD).
a1
(PO ) (M=Ca, Sr) are listed in Table 1. The atomic
4 2
The WinCSD program package [12] was used for an
ab initio structure solution. Finally, the full profile
structure refinement was carried out with the GSAS
coordinates, thermal parameters and main interatomic
distances are presented in Tables 2 and 3, respectively.
The experimental, calculated and difference X-ray
patterns for Na CaVO(PO ) are shown in Fig. 1.
[
13,14] program package. Further details of the crystal
2
4 2
Chernaya, Victoria V.
