Phase formation along the PO34/Zr = 1.5 Section of the ZrO(NO3)2-H3PO4-CsF-H 2O system

Article abstract of DOI:10.1134/S0036023612040080

The phase formation in the system ZrO(NO₃)₂ H ₃PO₄ CsF H₂O was studied along the section at the molar ratios PO^/Zr = 1.5 and CsF/Zr = 2-5 at a ZrO₂ concentration in the initial solution of 2-5 wt %. New fluorophosphate zirconates, CsH₂Zr₂F2(PO4)3 · 1.5H₂O and two modifications of CsZrF₂PO₄ · 0.5H ₂O, were isolated, and the known phosphate zirconate CsZr ₂(PO₄)₃ was obtained for the first time by calcining acidic fluorophosphate zirconate.

Full text of DOI:10.1134/S0036023612040080

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 4, pp. 492–498. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © M.M. Godneva, D.L. Motov, V.Ya. Kuznetsov, T.E. Shchur, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 4, pp. 554–559.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
3−
Phase Formation along the
= 1.5 Section
PO4 Zr
of the ZrO(NO3)2–H3PO4–CsF–H2O System
M. M. Godneva, D. L. Motov†, V. Ya. Kuznetsov, and T. E. Shchur
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Research Center, Russian
Academy of Sciences, ul. Fersmana 26A, Apatity, Murmansk oblast, 184200 Russia
Received April 27, 2010
Abstract—The phase formation in the system ZrO(NO3)2–H3PO4–CsF–H2O was studied along the section
3−
at the molar ratios
= 1.5 and CsF/Zr = 2–5 at a ZrO2 concentration in the initial solution of 2–5 wt %.
PO4 Zr
New fluorophosphate zirconates, CsH2Zr2F2(PO4)3 ⋅ 1.5H2O and two modifications of CsZrF2PO4 ⋅ 0.5H2O,
were isolated, and the known phosphate zirconate CsZr2(PO4)3 was obtained for the first time by calcining
acidic fluorophosphate zirconate.
DOI: 10.1134/S0036023612040080
†
We previously studied the phase formation in sulfuꢀ
The system ZrO(NO3)2–H3PO4–CsF–H2O was
studied along the section at the molar ratio F/Zr = 2–5
at 2–5 wt % ZrO2. The initial substances were
ric acid solutions of titanium subgroup element comꢀ
pounds in the presence of alkali metal fluorides [1].
Under “mild” synthesis conditions, we isolated about
a hundred of alkali metal fluorometallates and fluoroꢀ
sulfate metallates, most of which were obtained for the
first time. Investigation of a number of the compounds
showed that some of them are characterized by intense
Xꢀray luminescence. Xꢀray luminophores promising
for practical applications are hexafluorozirconates
ZrO(NO3)2
grade), and CsF (chemically pure). CsF was added
while continuously stirring to ZrO(NO3)2 2H2O soluꢀ
⋅ 2H2O and 85% H3PO4 (both of analytical
⋅
tions. After the mixtures became homogeneous,
H3PO4 was added to them. After keeping the obtained
mixtures for 7–45 days, precipitates were filtered off,
washed successively with water and alcohol, and dried
in air. The ZrO2 content in solution was calculated
with the consideration of H3PO4 before adding CsF.
Phases in the precipitates were identified by Xꢀray
powder diffraction, crystalꢀoptical, thermal, elemenꢀ
tal, and IR spectroscopic analyses. The Xꢀray powder
diffraction patterns were recorded with a DRFꢀ2
instrument (graphite monochromator, CuKα radiaꢀ
tion). The crystalꢀoptical measurements were perꢀ
formed using immersion liquids. The thermograms
were recorded in air using a Pt–Pt/Rh thermocouple.
The reference substance was calcined aluminum
oxide. The weight loss was determined with a VTꢀ1000
torsion balance at a heating rate of ~9 deg/min. The
IR spectra in the frequency range 400–3800 cm–1 were
recorded with a Specordꢀ80 spectrometer. Samples for
recording were prepared by compacting pellets with
KBr or CsI. The chemical analysis was carried out
according to standard procedures. The contents of
phosphorus, zirconium, and cesium were determined
by Xꢀray spectroscopy by the fundamental parameter
method with a Spectroscan MAKCꢀGV spectrometer;
fluorine after double distillation, by potentiometry;
NO3 group, by the Kjeldahl method; and water, by
thermogravimetry or from weight loss after keeping
M2Zr(Hf)F6 (M = K, Rb, Cs) and also Rb3Zr2F9SO4
⋅
2H2O [2, 3]. Two important results were obtained: on
the one hand, the synthesized materials exhibit relaꢀ
tively intense Xꢀray luminescence over a wide waveꢀ
length range, and on the other, it was found that the
efficiency of the Xꢀray luminescence efficiency can be
enhanced and its spectrum and temporal characterisꢀ
tics can be optimized by transforming some crystal latꢀ
tice defects to others, being Xꢀray luminescence cenꢀ
ters.
Phosphate zirconates CsZr2(PO4)3 [4, card 34ꢀ0196],
ꢀCs2Zr(PO4)2 [4, card 28ꢀ0356], and Cs3Zr1.5(PO4)3
α
[4, card 52ꢀ1181] are known. At low concentration of
the phosphorus component, we isolated crystalline
cesium fluorophosphate zirconate CsZrF2PO4
also amorphous oxofluorophosphate Cs2Zr3O2F4(PO4)2
3H2O and amorphous oxofluorophosphate nitrate
CsZr3O1.25F4(PO4)2(NO3)0.5 4.5H2O. The compound
Cs3Zr3O1.5F6(PO4)2 3H2O was obtained, which forms
in the crystalline or glassy state, depending on the conꢀ
ditions. The formation of the compounds
Cs2Zr3O1.5F5(PO4)2
and Zr3O4(PO4)1.33
⋅ H2O and
⋅
⋅
⋅
⋅
2H2O, Cs2Zr3F2(PO4)4
⋅ 4.5H2O,
⋅
6H2O was established, which crysꢀ
tallize only in mixtures with the known phases [5].
†
Deceased.
samples at 250°С in undried air.
492

PHASE FORMATION
493
Table 1. Formation of solid phases
Precipitate composition
Initialsolution: Addition:
ZrO2 content, F/Zr molar
chemical composition, wt %
phase
composition
wt %
ratio
P
O34–
N
O3–
+
–
Zr(IV)
Cs
F
H O
2
1.9
1.9
2
4.8
4.8
5
2
4
4.7
2
3
21.7
38.7
36.0
20.5
37.5
40.4
32.4
24.7
20.0
24.1
28.8
19.7
23.8
21.8
5.4
8.6
9.6
43.7
22.9
26.7
39.3
24.4
16.9
24.0
0
0
4.1
–
1.4
3.8
–
III
II
II
III, V
IV, V
IV, VI
I, II
3.6
5.6
3.6
3.2
2.2
5.8
14.8
10.3
19.5
3.8
5
5.4
–
4.8
Note: Phase notation: I–Cs ZrF , II–αꢀCsZrF PO ⋅ 0.5H O, III–CsH Zr F (PO ) ⋅ 1.5H O, IV–βꢀCsZrF PO ⋅ 0.5H O, V–phase y,
2 4 2 2 2 2 4 3 2 2 4 2
2
6
VI–CsNO .
3
The targeted synthesis of cesium fluorophosphate Fig. 1 shows a schematic of phase formation fields.
compounds was performed according to published
data [5, 6, 10].
Three singleꢀphase regions are outlined. With increasꢀ
ing molar ratio F/Zr, the phases that contain more fluꢀ
orine atoms, in particular, Cs2ZrF6, form and begin to
Table 1 presents selected data on the compositions
of the initial mixtures and isolated precipitates, and dominate in the system.
5
I, II
II
II
4
3
2
IV
IV
3600 3200
1600 1200 800 400
, cm–1
III
ν
1
III
3600 3200 1700 1300 900800 600 400
, cm–1
0
2
4
ZrO2, wt %
6
ν
Fig. 2. IR spectra of fluorophosphates zirconates The
Roman numerals at the curves are the phase numbers.
Spectra II and IV were recorded with a Specordꢀ80 specꢀ
trometer; spectrum III, a URꢀ20 spectrometer.
Fig. 1. Phase formation fields. The circles are experimental
points. The Roman numerals in the fields correspond to
the phase numbers.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

494
GODNEVA et al.
Table 2. Xꢀray powder diffraction data of cesium fluorophosphate zirconates
II III
IV
d
, Å
Irel
d
, Å
Irel
d
, Å
Irel
d
, Å
Irel
d
, Å
Irel
9.0
15
16
29
46
63
57
100
39
13
14
17
10
9
9.0
29
16
15
38
10
15
62
68
13
15
17
40
100
57
17
23
35
28
10
15
18
16
10
12
12
23
22
23
17
15
1.670
1.606
1.566
10
16
16
12.4
9.0
17
11
12
14
8
1.822
1.813
1.700
1.615
1.556
18
20
11
14
9
5.25
4.70
4.40
3.84
3.40
3.31
3.16
2.96
2.87
2.82
2.65
2.61
2.53
2.45
2.42
2.34
2.23
2.18
2.12
1.985
1.925
1.915
1.895
1.870
1.780
1.640
1.568
1.489
1.465
6.90
6.30
5.80
5.30
4.42
4.10
4.00
3.80
3.67
3.56
3.33
3.20
3.14
2.97
2.95
2.91
2.78
2.64
2.50
2.32
2.25
2.16
2.08
2.05
2.00
1.970
1.949
1.804
1.730
7.1
6.75
6.30
5.50
9
5.00
7
4.69
9
4.31
26
25
11
100
14
18
57
57
12
14
17
12
15
19
10
15
12
25
16
18
18
17
4.05
3.91
3.57
3.30
18
14
13
11
33
30
19
20
19
19
18
17
29
16
18
13
16
3.21
3.16**
2.99
2.90
2.82
2.63
2.56**
2.44
2.32
2.27
2.14
2.10
2.05
1.996**
1.960
1.904
1.855
* Cs ZrF , ** CsNO .
2
6
3
Table 2 provides the Xꢀray powder diffraction data vibrations of water. The strong absorption bands within
the range 900–1300 cm–1 are assigned to the vibrations of
the PO4 group. The zirconium–fluorine bands manifest
themselves at low frequencies (<550 cm–1) [7]. In anaꢀ
lyzing the IR spectra, we were proceeded from the fact
on crystalline cesium fluorophosphate zirconates,
which have no analogues in the ICDD database.
The IR spectra of cesium fluorophosphate zirconate
(Fig. 2) contain absorption bands due to the bending
(1500–1730 cm–1) and stretching (3300–3650 cm–1) that the symmetry of the tetrahedral РО4 group
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

PHASE FORMATION
495
Table 3. Wavenumbers (cm–1) of absorption bands in IR
reduces in the following cases: as this group coordiꢀ
nates to Zr, for terminal groups as compared to bridgꢀ
ing ones, in the transition from transꢀ to cisꢀisomers,
and in the interaction of PO4 groups with hydrogen to
give hydrophosphate groups.
spectra
Assignment
II
III
IV
[7, 9]
In diluted (2 wt % ZrO2) solutions at the molar
ratio F/Zr > 3, phase II forms, which contains less
300
320
300
340
PO34−
water than at lower concentration of
groups
3−
(
= 0.5) [5].
PO4 Zr
380 n
–
ν
(Zr–F–Zr)
For CsZrF2PO4
⋅
0.5 H2O anal. calcd. (wt %): Cs+
,
3−
36.3; Zr(IV), 24.92; F– 10.38;
25.94; H2O 2.46.
PO4
,
36.0; Zr(IV), 24.1; F– 9.6;
400
450
420
ν(Zr–F)
3−
PO4
Found, wt %: Cs+
26.7; H2O 2.0.
470 st
480 n
510
According to the IR spectrum, the phase contains
a trisubstituted phosphate group (Table 3). The splitꢀ
ting of the bands ν3 and ν4 can be caused by the coorꢀ
dination of PO4 groups to zirconium and also by the
formation of cis and trans isomers [8]. Two absorption
bands due to water stretching vibrations and a step in
the bending vibration band are because of the presence
of two types of water molecules with different hydroꢀ
gen bond strengths. The absence of water rotational
480
520 n
535
δ (PO ),
as 4
ν
(Zr–F)
580
620 n
640
580 st
550
600
620
ν
(PO )
4
4
vibrations
phase is crystallization water [7]. After dewatering, the
product is virtually thermally stable until 720 , at
ρ in phase II indicates that the water in this
625 b
660
δ(PO )
4
°С
650 n
which temperature it is likely to incongruently melt
(Fig. 3).
740 b w
770 b
ρ(MꢀOH ),
2
γ
(POH)
(PO(H))
(MꢀOH ),
The composition of phase II is similar to the comꢀ
position CsZrF2PO4 · H2O obtained previously at the
820 w
ν
3−
molar ratio
= 0.5 [5]. The two compounds
PO4 Zr
are characterized by similar, but not identical, Xꢀray
powder diffraction patterns and different crystal
shapes, with the refractive index being higher for
hemihydrate (Table 4). Their IR spectra are also difꢀ
ferent. After heating to ∼1000°С, Cs2Zr(PO4)2 and
monoclinic ZrO2 were found in the heating product,
which confirmed the composition of the initial phase.
Phase III is represented by uniform granular crysꢀ
tals
900 n
ρ
2
ν
(PO(H))
1000 vs
1050
930 n
1020
ν
(PO )
1
4
ν
(PO )
4
3
1040 s
1090
1080 s
1230
For CsH2Zr2F2(PO4)3 ⋅ 1.5 H2O anal. calcd. (wt %):
1140
1180
1120
3−
Cs+
,
19.91; Zr(IV), 27.33; F– 5.69;
42.69; H2O
PO4
4.05. Found, wt %: Cs+
,
20.9; Zr(IV), 26.9; F– 5.4;
1200
PO34−
42.9; H2O 4.2.
1630
1600 st
1630
δ(H–O–H)
The IR spectra of hydrophosphates are characterꢀ
ized by the presence of bands at the frequencies 700–
900, 860–915, 1210–1400, and 2600–3250 cm–1,
1650 st
1680
which are assigned to the vibrations
(PO(H)), (POH), and (OH), respectively [9]. The
spectrum of phase III exhibits absorption at 1230 and
2850 cm–1 but does not show the vibrations
(POH)
and (PO(H)). In this compound, hydrogen is likely to be
bonded to fluorine, rather than to the PO4 group. Within
the range of vibrations of PO4 groups, the spectrum is simꢀ
ilar to those of the compounds М3H3Zr3F3(PO4)5 (M = K
or Rb) [6, 10], to which the formulas of phosphatohydroꢀ
phosphates М3Zr3F3(HPO4)3(PO4)2 were assigned.
γ(POH),
2850 w b
ν
(OH)
ν
δ
ν
3300
3450
3550
ν(O–H)
γ
ν
3480
3580
3500 b w
Note: b, broad; n, narrow; s, strong; st, step; vs, very strong; w,
weak.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

496
GODNEVA et al.
As judged from its composition and structure
ΔT, °C
(Table 2), phase IV is a modification of phase II. The
IR spectrum of phase IV contains the bands that can
be simultaneously assigned both to the vibrations of
the HPO4 group and to the wagging and rocking vibraꢀ
tions of water, which are characteristic of water coorꢀ
dinated to zirconium. The number of absorption
bands of PO4 groups in the spectrum of phase IV is
much larger than that in the spectrum of phase II; i.e.,
the former groups are less symmetric, which can be
explained both by the hydrogen bond in the hydroꢀ
phosphate group and by the cis isomerism in phase IV
as compared to the cis–trans isomerism in phase II [7].
Three absorption bands due to water stretching vibraꢀ
tions and a step in the bending vibration band are
because of the presence of two types of water moleꢀ
cules.
102
117
550
1
723
241
906
536
523
260
650
693
721
2
752
657
76
344
3
781
385
452
700
145
τ, min
The lowꢀtemperature (241–260°С) endothermic
event in the differential thermal analysis curve is
caused by water removal; then, an amorphous product
Fig. 3. Differential thermal analysis curves of cesium fluoꢀ
rophosphate zirconates ( ꢀCsZrF PO 0.5H O, (
CsZrF PO 0.5H O, and (
1)
α
⋅
2) βꢀ
2
4
2
2
4 3
⋅
3)
CsZr (PO )
⋅
2HF
⋅
crystallizes (exothermal event at 523–536
water removal up to 420 , the weight loss is 1.6%.
The main loss occurs above 600 . The last endotherꢀ
mic event (752–781 ) is caused by decomposition to
°С). After
2
4
2
1.5H O at sample weights of (
1) 0.20, (2) 0.13 and (3) 0.18 g
2
°С
at a heating rate of 9 K/min.
°С
°С
form a mixture of solid phases of the gross composiꢀ
tion CsZrO1.75(PO4)0.5, which contains ZrO2 and,
After water removal, no weight loss is observed until
320 . Then, within the range 320–460 , there is a
°С
°С
probably, Cs2ZrO1.5PO4
.
3.2% weight loss, which is approximately a half of the
total HF loss. In this case, the composition of the product
after the endothermic event is CsHZr2F(PO4)3. The litꢀ
tle excess over the theoretical value (6.02%) is caused
by the insignificant formation of polyphosphates. The
final calcination product is CsZr2(PO4)3 (Table 5). No
lines due to polyphosphates are seen in the Xꢀray powꢀ
der diffraction pattern.
The total weight loss at
∼1000°С is 15.2 wt %,
which exceeds the theoretical weight loss due to fluoꢀ
rine by 4.5%. Isothermal calcination at the same temꢀ
perature leads to a 25% weight loss, which is caused by
the transformation of phosphate to polyphosphate.
The final calcination product is fireꢀpolished and
changes to a sticky mass because of hygroscopicity
while being ground to a powder. Few weak lines in the
Xꢀray powder diffraction pattern are unidentifiable.
Phase IV crystallizes with impurities. From a mixꢀ
ture of this phase and CsNO3, mechanically large
CsNO3 crystals were removed. The composition of the
residue was found.
Phase V (denoted by y) is amorphous and is not isoꢀ
lated individually; its composition is not found.
The compounds mainly form small crystals 2–6
in size.
μm
For CsZrF2PO4 ⋅ ,
0.5 H2O anal. calcd. (wt %): Cs+
3−
36.3; Zr(IV), 24.92; F– 10.38;
25.94; H2O 2.46.
3−
PO4
Found, wt %: Cs+
24.4; H2O 3.2.
,
37.5; Zr(IV), 25.2; F– 10.3;
PO4
Approximate schemes of thermal decompositions
are the following:
Table 4. Crystalꢀoptical characteristics
Phase
Crystal shape
N
N
p
g
II
Radiated aggregates
Spherolites, uniform granular
Needle
1.580
1.560–1.580
1.545*
1.540
1.530
III
IV
V
Undetermined
1.595*
* Average value.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

PHASE FORMATION
Table 5. Xꢀray powder diffraction data of calcination products
497
II
III
IV
3
1000
°
C
480
°C
970
°
C
760°C
d
, Å
Irel
d
, Å
Irel
d
, Å
Irel
d
, Å
Irel
1
2
9.4
9
17
49
19
100
79
7
6.30
5.60
5.00
4.49
3.98
3.81
3.60
3.40
3.16
3.09
2.88
2.59
2.50
2.22
2.14
2.12
1.994
1.862
1.820
1.775
1.727
1.717
1.698
1.680
18
20
18
100
50
31
21
59
46
84
92
30
43
37
37
35
20
35
35
21
31
37
41
36
4.30
82
37
10
8
5.0
13
12
17
6
1
4.72
4.20
3.70
3.32
3.15
3.03
2.84
2.71
2.61
2.53
2.36
2.28
2.21
2.14
2.11
2.05
2.02
3.82
4.61
4.47
4.21
3.67
3.43
3.29
3.20
3.16
3.05
2.83
2.75
2.68
2.61
2.50
2.48
2.26
2.22
2.17
2.08
2.04
2.01
1
3.58
2
3.20
1
2
2.99
100
16
10
30
7
19
100
82
84
67
17
30
58
30
16
14
12
10
16
22
10
19
17
10
14
16
23
19
12
18
18
18
12
2.90
2.75
2
12
39
8
2.48
1
2
2
2.40
2
2.34
3
12
5
2.13
32
12
35
14
3
24
16
6
2.08
1
2
1.907
1.860
1.780
1.720
1.623
1.595
1.508
1.430
1.352
1.319
1.278
1.233
2
5
1
1
50
32
9
8
20
23
21
5
1.863
1.818
1.750
1.694
1.661
1.570
1.545
1.472
1.410
1.402
1.367
1.293
1.254
1.132
14
8
2
19
4
9
2
2
4
5
6
1.980
1.925
1.880
1.843
1.820
1.723
1.680
1.662
1.635
23
7
9
2
2
7
13
8
20
12
7
11
(1)
(2)
(3)
Note: The superscripts at the numbers refer to the following: Cs Zr (PO ) (4, card 52ꢀ1181), ZrO (4, card 36ꢀ420), and isoꢀ
3
1.5
4 3
2
thermal calcination.
2αꢀCsZrF2PO4 · 0.5H2O
βꢀCsZrF2PO4 · 0.5H2O
102–117°C
241–260°C
⎯⎯⎯⎯⎯→ 2αꢀCsZrF2PO4
⎯⎯⎯⎯⎯→ βꢀCsZrF2PO4
721–723°C
523–536°C
⎯⎯⎯⎯⎯→ Cs Zr PO + ZrO2;
(
)
⎯⎯⎯⎯⎯⎯→ βꢀCsZrF2PO4
crystallization
2
4
2
780°С
⎯⎯⎯⎯→ Cs2ZrO1.5PO4 + ZrO2.
CsH Zr F PO · 1.5H2O
(
)
2
2
2
4
3
3−
76–145°C
Thus, at the molar ratio
= 1.5, new fluoꢀ
PO4 Zr
⎯⎯⎯⎯⎯→ CsH Zr F PO
4
(
)
3
2
2
2
rophosphate zirconates, CsH2Zr2F2(PO4)3
and two modifications of CsZrF2PO4 0.5H2O, were
isolated from solution, and a singleꢀphase product,
⋅ 1.5H2O
320–460°C
⎯⎯⎯⎯⎯→ CsHZr F PO
(
)
3
2
4
⋅
970°C
⎯⎯⎯⎯→CsZr2(PO4)3;
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012

498
GODNEVA et al.
5. M. M. Godneva, D. L. Motov, and M. P. Rys’kina,
Russ. J. Inorg. Chem. 56, 1363 (2011).
6. M. M. Godneva, D. L. Motov, and V. Ya. Kuznetsov,
phosphate zirconate CsZr2(PO4)3, was obtained by
calcining acidic fluorophosphate zirconate.
Russ. J. Inorg. Chem. 53, 1654 (2008).
REFERENCES
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9. V. V. Pechkovskii, R. Ya. Mel’nikova, E. D. Dzyuba,
et al., Atlas of Infrared Spectra of Phosphates: Orthoꢀ
phosphates (Nauka, Moscow, 1981) [in Russian].
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nium Group Elements: Sulfates, Fluorides, and Fluoroꢀ
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 4 2012