Synthesis and homogeneity range of Yb8−xYxV2O17 in the Yb8V2O17–Y8V2O17 system
Synthesis and homogeneity range of Yb82xYxV2O17 in the Yb8V2O17-Y8V2O17 system
Mateusz Piz 0
Elzbieta Filipek 0
0 Department of Inorganic and Analytical Chemistry, Faculty of Chemical Technology and Engineering, West Pomeranian University of Technology , Szczecin, Al. Piastow 42, 71-065 Szczecin , Poland
New substitutional limited solid solution of the formula Yb8-xYxV2O17 and 0 \ x \ 4.0 was synthesised by the solid-state reaction from the mixtures of the compounds Yb8V2O17 and Y8V2O17. The monophasic samples containing Yb8-xYxV2O17 were characterised by powder XRD, DTA, IR, UV-Vis-DRS and SEM methods. The influence of the degree of Y3? ion incorporation in the crystal lattice of Yb8V2O17 replacing Yb3? ions, on the thermal stability, unit cell volume, band gap energies as well as on the position of the IR absorption bands in the spectrum of Yb8-xYxV2O17 was determined. The morphology of Yb8V2O17 and solid solution was analysed.
Solid solution; Solid-solid reaction; Thermal stability; XRD; Yb8-xYxV2O17
Yttrium vanadates(V) doped with rare earth metals have
been for a few decades the subject of interest because of
their unique and attractive physicochemical properties and
have been applied in many branches of industry [1?13].
Yttrium orthovanadates(V) doped with Nd3?, Er3? or Yb3?
ions make interesting laser materials employed in lasers
used in medicine or electronic industry [1?7]. YVO4 doped
with Nd3?, Yb3?, Eu3?, Bi3? or Er3? ions has been applied
as a luminophore or for production of plasma displays,
electroluminescent diodes or fluorescence lamps [8?13].
Many scientific reports have been devoted to yttrium or
ytterbium orthovanadates(V) [1?18], but much less
attention has been paid to other vanadates(V) forming in the
binary systems V2O5?Yb2O3 and V2O5?Y2O3, that is to the
compounds Yb8V2O17 and Y8V2O17 [19?22]. The first of
them Yb8V2O17 has been for the first time obtained by
Brusset et al.  as a result of heating of a mixture of
oxides Yb2O3/V2O5 at the molar ratio 4:1 to 1550 C. This
compound crystallises in the monoclinic system, and the
parameters of its elementary cell are: a = 1.0397 nm,
b = 0.8242 nm, c = 1.5891 nm, b = 98.47 . The
same authors  constructed the phase diagram of V2O5?
Yb2O3, taking into account the formation of YbVO4 and
According to literature data on the system V2O5?Y2O3
[21, 22], the compound Y8V2O17 has been obtained as a
result of heating a mixture of oxides Y2O3/V2O5 at the
molar ratio 4:1 at 1549 C  and by the alkoxy method
from VO(OC2H5)3 and YCl3 . The authors of  have
washed the sediment obtained many times with hot water
and then after drying, subjected the sediment to calcination
at 1500 C. However, the X-ray structural data for the
compound Y8V2O17 obtained by the above-mentioned two
methods are significantly different [21, 22]. The authors of
[21, 22] agree that Y8V2O17 occurs in two polymorphic
varieties and that the low-temperature variety of Y8V2O17
undergoes a monotropic phase transition to the
high-temperature variety at 1550 C. Only Yamaguchi et al. 
have reported that the low-temperature variety crystallises
in tetragonal system, while the high-temperature one in
monoclinic system and determined the parameters of their
The state of knowledge on Yb8V2O17 and Y8V2O17, and
in particular the lack of information on their thermal
stability and incomplete information on their structures, has
prompted us to supplement the gap.
Taking into account the fact that the title pseudo-binary
system Yb8V2O17?Y8V2O17 has not been studied yet, the
general aim of our study was to which phases?if any?form
as a result of reaction between the components of this
system, determination of their thermal stability and basic
physicochemical properties. These new phases can
potentially find similar or wider application than the already
known ones formed with yttrium orthovanadate(V) or
orthovanadates of rare earth elements.
The following reagents were used in our experiments:
Yb2O3, a.p. (Alfa Aesar, Germany), Y2O3, a.p. (Alfa Aesar,
Germany), V2O5, a.p. (POCh, Poland). The components of
investigated system, i.e. Yb8V2O17 and Y8V2O17, were
obtained by heating in air the mixtures of V2O5/Yb2O3 and
V2O5/Y2O3 at the molar ratio of 1:4 in the temperature
range 600?1300 C [19, 21].
Nine samples were prepared for the experiments. The
samples were contained from 5.00 to 62.50 mol% of
Y8V2O17 in mixtures with Yb8V2O17. The solid solution,
Yb82xYxV2O17, where 0 \ x \ 4, was prepared by the
high-temperature solid-state reaction from the compounds:
Yb8V2O17 and Y8V2O17 by the method described inter alia
in [23?26]. Reagents weighed in suitable proportions were
homogenised and calcined in air atmosphere in the
temperature range 1400?1600 C. The samples were heated in
a tube furnace PRC 50/170/M (Czylok, Poland) equipped
with a stationary optical pyrometer MARATHON MM
(Raytek, Germany). The optical pyrometer was calibrated
to the melting points of Ca2P2O7 (1353 C), CaF2
(1420 C) and Na3PO4 (1583 C). After each heating
stage, the samples were gradually cooled in the furnace to
room temperature and analysed by the powder XRD or
DTA methods too. The powder diffraction patterns of the
samples obtained were recorded with the aid of the
diffractometer EMPYREAN II (PANalytical, Netherlands)
using CuKa with graphite monochromator. The phases
were identified on the basis of XRD characteristics
presented in the PDF cards . The powder diffraction
pattern of Yb82xYxV2O17 was indexed in analogy to other
phases , i.e. by means of the POWDER program .
The parameters of selected unit cell were refined using the
REFINEMENT program of DHN/PDS package.
The DTA study was performed using an SDT 2960
thermoanalyser (TA Instruments, USA) under the air flow
(110 mL min-1), at the heating rate of 10 min-1 in
temperatures from the range 20?1450 C. The DTA
method for testing the thermal stability of the various
phases forming in the multicomponent oxide systems was
described, inter alia, in [30?33].
Selected samples were investigated also by means of an
electron scanning microscope?SEM (JSM-6100, Jeol,
Japan). The densities of Yb82xYxV2O17 were determined
in argon (5 N purity) with the help of an Ultrapyc 1200e
ultrapycnometer (Quantachrome Instruments, USA). Initial
mixtures and monophasic samples were examined by IR
spectroscopy. The measurements were made within the
wavenumber range of 1200?250 cm-1, using a
spectrophotometer SPECORD M-80 (Carl Zeiss, Jena,
Germany). A technique of pressing pellets with KBr at the
mass ratio of 1:300 was applied. The UV?Vis?DR spectra
were measured using a UV?Vis spectrometer V-670
(JASCO, Japan) equipped with a reflecting attachment for
the solid-state investigation (integrating sphere attachment
with horizontal sample platform PIV-756/(PIN-757). The
spectra were recorded in the wavelength region of
200?750 nm at room temperature.
Results and discussion
The first stage of the study was to verify the literature
crystallographic data [19?22] on the compounds Yb8V2O17
and Y8V2O17 and to evaluate their thermal stability.
Analysis of XRD diffractograms of Yb8V2O17 and the
lowtemperature polymorph of Y8V2O17 synthesised by us
revealed that only the diffractogram of Yb8V2O17 differed
slightly from that reported by Brusset et al. . Because
of these differences including the presence of additional
low-intensity XRD lines (d = 0.4675; 0.4492; 0.3911 nm),
the Yb8V2O17 diffractogram was subjected to indexation
using the program POWDER .
Indexation was performed for selected 20 reflections
from the range of 2h angles from 6 to 40 (CuKa). The best
agreement with experimental data was obtained for the
triclinic elementary cell model. The results of indexation of
the powder diffractogram of Yb8V2O17 are presented in
The elementary cell parameters of Yb8V2O17 were
refined with the use of the program REFINEMENT
(package DHN/PDS) to be:
? a = 0.8932 nm, b = 0.9259 nm, c = 0.9794 nm,
? a = 77.684 , b = 106.367 , c = 116.348
? elementary cell volume V = 0.6928 nm3,
? number of molecules in the elementary cell Z = 2.
The quality coefficient for this refined solution is
F(20) = 12.37 (0.0192.84). The calculated density of
Yb8V2O17 for the selected solution is equal to 8.42 g cm23
Table 1 Results of indexation of the powder diffractogram of
and experimentally determined with a gas ultrapycnometer
was 8.26 ? 0.05 g cm23. The difference in densities is
probably connected with porosity of obtained compound.
As the solution proposed by us is significantly different
from that given in  from 1973, we decided to refine the
Yb8V2O17 diffractogram known from literature with the
use of program REFINEMENT. For the solution proposed
by the authors of  which was the monoclinic system,
the quality coefficient FM was very low, of only 2.24,
which indicated a very small probability of crystallisation
of this compound in the monoclinic system.
As thermal stability of the compounds Yb8V2O17 and
Y8V2O17 has not been known, they were subjected to
DTA?TG measurements in air atmosphere and in the
temperature range 20?1450 C. In this range no thermal
effects were observed on both DTA and TG curves. This
result means that these compounds undergo decomposition
or melting at temperatures higher than 1450 C. In view of
this result, the study of reactivity between Yb8V2O17 and
Y8V2O17 was started from a lower temperature of 1400 C.
The mixtures of Yb8V2O17 and Y8V2O17 of compositions
specified in Table 2, were heated at the following stages:
I:1400 C (24 h) ? II:1450 C (24 h) ? III:1500 C
(24 h) ? IV:1550 C (24 h).
As evidenced by XRD analysis, already after the first
stage of heating the phase composition of all samples
changed. The XRD diffractograms recorded for samples
1?7 did not reveal the reflections characteristic of
Y8V2O17, and besides the lines characteristic of Yb8V2O17
slightly shifted towards smaller angles 2h, it showed the
lines undoubtedly evidencing the presence of YVO4 and
Yb2O3. The subsequent two stages of the sample heating, at
1450 and 1500 C, did not cause changes in the phase
composition but changed the proportion of phases, i.e. the
phases YVO4 and Yb2O3 were present in small amounts.
The diffractograms recorded after the last stage of heating
showed only the lines characteristic of Yb8V2O17. With
increasing content of Y8V2O17 in the initial mixtures of
reagents, the lines were increasingly shifted towards
smaller 2h angles that evidenced increasing interplanar
distances dhkl relative to those in undoped Yb8V2O17 .
According to these results, in the system Yb8V2O17?
Y8V2O17 in the concentration range studied, the reactions
leading to formation of substitutive solid solution in which
Y3? replaced Yb3? in the crystalline lattice of Yb8V2O17
took place. It is highly probable because of similar values
of ionic rings of Yb3? and Y3? that can occur in the
polyhedrons of NC = 6 (Yb3?-86.8 pm and Y3?-90.0 pm)
as well as of NC = 8 (Yb3?-98.5 pm and Y3?-101.9 pm)
. The method for synthesis of this solid solution has
been applied for patent protection in Poland .
According to phase composition determination in
samples 8 and 9, representing the concentration ranges of the
system components above 40.00 mol% Y8V2O17, after the
last stage of heating (1550 C) the samples were biphasic
and besides the Yb8-xYxV2O17 contained the
high-temperature polymorph of Y8V2O17 (Table 2).
The phase composition of all samples after the last stage
of heating, presented in Table 2, shows that the solid
solution formed in the system is substitutive, of limited solubility
of components and general formula Yb8?xYxV2O17. The
results collected in Table 2 additionally imply that the
maximum degree of Y3? ions incorporation into Yb8V2O17
reaches at least 40.00% mol (x = 3.2) and does not exceed
50.00% mol. The above-discussed results lead to the
conclusion that in the reaction mixtures studied the following
reaction took place:
?1 0:125x?Yb8V2O17?s? ? 0:125x Y8V2O17?s?
? Yb8 xYxV2O17 ?s:s:?
Figure 1 presents a fragment of XRD diffractogram of
Yb8V2O17 (Fig. 1a) to be compared with the analogous
fragments of diffractograms of the new solid solution
Yb8-xYxV2O17 for x = 0.8 (Fig. 1b), x = 2.8 (Fig. 1c) and
x = 3.2 (Fig. 1d).
At the next stage of the study our aim was to confirm
that the new solid solution Yb8-xYxV2O17 has the structure
of the matrix, that is it crystallises in the triclinic system.
x in Yb8-xYxV2O17
Fig. 1 Fragments of diffractograms of: a Yb8V2O17, b
Yb7.2Y0.8V2O17, c Yb5.2Y2.8V2O17, d Yb4.8Y3.2V2O17
Thus, the powder diffractograms of the new solution
Yb8-xYxV2O17 for x = 0.80; 2.00; 2.80 and 3.20 were
subjected to indexation. The elementary cell parameters
were refined with the program REFINEMENT. The results
confirmed that the new solid solution crystallises in the
triclinic system and permitted calculation of the parameters
of its elementary cell as a function of the degree of Yb3?
Phase composition of
samples after synthesis
substitution with Y3? in the crystal lattice of Yb8V2O17.
Table 3 presents the elementary cell parameters, their
volumes and densities for Yb8-xYxV2O17 with x = 0.00;
0.80; 2.00; 2.80 and 3.20.
According to the data presented in Table 3, with
increasing x in Yb8-xYxV2O17, that is with increasing
degree of Yb3? substitution with Y3?, the crystal lattice
expansion takes place; that is the elementary cell volume
increases with respect to that of the matrix Yb8V2O17.
Moreover, the density of the solid solution determined with
the use of a gas ultrapycnometer is lower than the value
calculated on the basis of parameters selected elementary
With increasing x in Yb8-xYxV2O17 a change in its
colour from orange to yellow was observed.
At the subsequent stage the compound Yb8V2O17 and
the solid solution Yb8-xYxV2O17 with x = 3.2 were
studied by scanning electron microscopy (SEM). The SEM
images of the two polycrystalline samples are presented in
Figs. 2 and 3.
The morphology of the solid solution Yb8-xYxV2O17
crystallites is very similar to that of the matrix Yb8V2O17.
They look like polygons of irregular shapes and different
sizes, varying from 1 to 8 lm (Fig. 3). It should be pointed
out that some crystallites of the matrix have ball-like shape
of diameters close to *6 lm (Fig. 2).
As the structures of Yb8V2O17 and the solid solution
Yb8-xYxV2O17 were not fully resolved, their IR spectra
were measured to get some preliminary information on the
type of metal oxide polyhedrons in structures these phases.
Figure 4 presents the IR spectra of Yb8V2O17 (Fig. 4a) and
the newly obtained solid solution Yb8?xYxV2O17 with
x = 0.80; 2.80 and 3.20 (Fig. 4b?d).
The IR spectrum of Yb8V2O17 (Fig. 4a) shows a few
absorption bands of maxima appearing at 940, 820,
450 cm-1. The bands in the wavenumber range
Table 3 Unit cell parameters, volumes and densities for Yb8V2O17 and solid solutions Yb8-xYxV2O17
x in Yb8-xYxV2O17
Fig. 2 SEM image of Yb8V2O17
Fig. 3 SEM image of Yb8-xYxV2O17 (x = 3.2)
970?620 cm-1 can be assigned to stretching vibrations of
the symmetric and asymmetric V?O bonds in VO4
tetrahedrons and to the vibrations of Yb?O bonds in the YbO6
octahedrons [36?38]. The presence of YbO8 polyhedrons
cannot be excluded . On the basis of the IR spectrum of
ytterbium vanadate(V) of the known structure [36?38] the
absorption band in the range 650?300 cm-1 can be assigned
to bending vibrations of V?O bonds in VO4 tetrahedrons and
the band at *630 cm-1 can be attributed to V?O?V bond.
On the other hand a broad band with a maximum at
450 cm-1 can likely be attributed to the stretching vibrations
of M?O bonds in the YbO6 octahedrons [36?38].
As follows from analysis of the IR spectrum of the new
solid solution (Fig. 4b?d) the positions of absorption bands
in this spectrum are very similar to those in the IR spectrum
of Yb8V2O17. With increasing degree of Y3? incorporation
to replace Yb3? in the crystal lattice of Yb8V2O17, the
positions of absorption bands shift towards smaller
Fig. 4 Fragments of the IR spectra of: a Yb8V2O17, b Yb7.2Y0.8V2
O17, c Yb5.2Y2.8V2O17, d Yb4.8Y3.2V2O17
wavenumbers or remain unchanged with respect to their
positions in the IR spectrum of the matrix. The results of
this part of study confirmed that the solid solution
Yb8?xYxV2O17 shows the structure of Yb8V2O17, so contains
VO4 tetrahedrons and MO6 polyhedrons (M=Y and Yb) or/
and YbO8 [36?39]. It is not possible to conclude from IR
spectra on the way the polyhedron is joined and therefore
studies are only qualitative.
In order to assess the thermal stability of Yb8V2O17 and
the solid solution Yb4.8Y3.2V2O17 obtained at 1550 C, the
samples containing these two phases were heated from
1450 to 1700 ? 20 C in air atmosphere in a horizontal
tube furnace equipped with an optical pyrometer.
The samples heated to 1600 C did not show signs of
melting, and their phase composition was unchanged. The
diffractograms of the samples heated up to *1650 C
show the set of XRD lines which, according to the PDF
chart no. 00-035-0153, were assigned to the
high-temperature polymorph of Yb8V2O17.
Fig. 5 Fragments of diffractograms of samples were heated at
*1700 C: a Yb8V2O17 b Yb4.8Y3.2V2O17
Fig. 6 Kubelka?Munk transformation of reflectance spectra of
Yb8V2O17 and the solid solution Yb8?xYxV2O17 for x = 0.80; 2.80;
The lines in the diffractogram of Yb4.8Y3.2V2O17
corresponded to slightly greater interplanar distances, which
suggest the presence of the solid solution Yb8?xYxV2O17,
as the high-temperature polymorph of Yb8V2O17 is its
matrix. The results obtained at this stage imply that at
1650 ? 20 C the compound Yb8V2O17 undergoes
monotropic polymorphous transformation.
Heating of the samples up to *1700 C did not result in
their melting and did not cause changes in their phase
composition. As we have no possibility to heat the samples
above 1700 C, we could only conclude that the
hightemperature polymorph of Yb8V2O17 and the solid solution
of the same structure are thermally stable in air at least to
*1700 C. Figure 5 presents a fragment of XRD
diffractogram of Yb8V2O17 (Fig. 5a) with the analogous fragment
of diffractogram of Yb4.8Y3.2V2O17 (of the new solid
solution Yb8-xYxV2O17 for x = 3.2), i.e. of samples which
were heated at *1700 C (Fig. 5b).
Literature data  on the high-temperature polymorph
of Yb8V2O17 are fragmentary so the studies should be
continued to provide its physicochemical characterisation
and detail structure.
In this study the physicochemical characterisation of
Yb8V2O17 and the solid solution Yb8-xYxV2O17 was
extended by the UV?Vis?DR measurements that helped
evaluate the energy gap for these phases.
The reflectance spectra of Yb8V2O17 and the solid
solution Yb8?xYxV2O17 for x = 0.80; 2.80; 3.20 after
Kubelka?Munk transformation are shown in Fig. 6.
The Kubelka?Munk transformation of measured
reflectance performed using package Spectra Manager Version 2
(Spectra Analysis program) according to equation:
where K is reflectance transformed according to Kubelka?
Munk and R is reflectance (%).
Then plotted the relationship (K hm)2 = f(hm)?see
Fig. 6, where on the ordinate variable (K/M) means
(K hm)2. The intersection between the linear fit and the
photon energy axis gives the value to Eg.
The energy gap (Eg) obtained for the compound
Yb8V2O17 is *2.60 eV, while the energy gap for the solid
solution Yb8?xYxV2O17 evaluated by UV?Vis?DR method
decreases with increasing degree of substitution x from
Eg = * 2.52 eV for Yb7.2Y0.8V2O17 to *2.44 eV for
Yb4.8Y3.2V2O17. The above energy gap values mean that
both the compound Yb8V2O17 and the solid solution
Yb8-xYxV2O17 are semiconductors.
The substitutional, limited solid solution of the formula
Yb8-xYxV2O17 and 0 \ x \ 4.0 is formed in the
This phase has been obtained in air by high-temperature
reaction from the specially synthesised compounds:
Yb8V2O17 and Y8V2O17.
Yb8-xYxV2O17 crystalises in the triclinic system.
With increasing x in Yb8-xYxV2O17, the crystal lattice
of solid solution expands.
The solid solution Yb8-xYxV2O17 is stable in air
atmosphere up to *1700 C.
Yb8V2O17 and Yb8-xYxV2O17 belong to the group of
semiconductors with the band gab energies from 2.60 to
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