Phase formation in the Ag2MoO4-MgMoO 4-Al2(MoO4)3 system

Article abstract of DOI:10.1134/S0036023610060203

The subsolidus region of the Ag₂MoO₄-MgMoO ₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag _1-xMg_1-xAl_1+x(MoO₄)₃ (0 ≥ x ≥ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_1-xMg_1-xAl_{1 + x}(MoO ₄)₃ variable-composition phase is related to the NASICON type structure (space group R 3? c). AgMg₃Al(MoO ₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P 1?, Z = 2) with the following unit cell parameters: α = 9.295(7) ?, b = 17.619(2) ?, c = 6.8570(7) ?, α = 87.420(9)°, β = 101.109(9)°,. = 91.847(9)°. The compounds Ag _{1 - x}Mg_{1 - x}Al_{1 + x}(MoO₄) ₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036023610060203

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 6, pp. 955–958. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.Yu. Kotova, V.P. Korsun, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 6, pp. 1022–1025.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Formation in the Ag2MoO4–MgMoO4–Al2(MoO4)3 System
I. Yu. Kotova and V. P. Korsun
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, UlanꢀUde, Buryat Republic, Russia
Received December 18, 2008
Abstract—The subsolidus region of the Ag2MoO4
ied by Xꢀray phase analysis. The formation of new compounds Ag1 – xMg1 – xAl1 + x(MoO4)3 (0
AgMg3Al(MoO4)5 has been determined. The Ag1 – xMg1 – xAl1 + x(MoO4)3 variableꢀcomposition phase is
–MgMoO4
–
Al2(MoO4)3 ternary salt system has been studꢀ
≤ ≤
x
0.4) and
related to the NASICON type structure (space group ). AgMg3Al(MoO4)5 is isostructural to sodium magꢀ
nesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group = 2)
with the following unit cell parameters: = 9.295(7) Å, = 17.619(2) Å, = 6.8570(7) Å, = 87.420(9)°,
R3 c
P1 , Z
a
b
c
α
β
= 101.109(9)°, = 91.847(9)°. The compounds Ag1 – xMg1 – xAl1 + x(MoO4)3 and AgMg3Al(MoO4)5 are
γ
thermally stable up to 790 and 820°C, respectively.
DOI: 10.1134/S0036023610060203
The demands of new industries and the advances in equilibrium was attained, the phase composition was
a number of new scientific and engineering lines stimꢀ
ulate investigations in the field of multicomponent
systems and the development and synthesis of new
solidꢀphase materials with a designed set of properties.
Now a highly important place in the search and creꢀ
ation of new complex oxide materials offering promise
as ionic semiconductors is held by compounds that
demonstrate crystallochemical similarity to NASIꢀ
CONꢀtype compounds [1–5].
This work studies phase formation in the subsolidus
region of the silver magnesium aluminum molybdate
system and determines the Xꢀray diffraction and therꢀ
mal characteristics of triple molybdates and the condiꢀ
tions for their synthesis.
studied by Xꢀray diffraction.
To ascertain a possible homogeneity region in the
Ag2MoO4–MgMoO4–Al2(MoO4)3 system, Ag1 – xA1 –
Al1 + x(MoO4)3 samples were prepared in
x
Δ
x = 0.1 steps
within the range 0.7 and stepwise annealed in air
0
≤ ≤
x
in steps of 50°С starting at 300°С with intermediate
grinding every 20–30 h. The duration of annealing was
50–100 h at every temperature. The homogeneity
region boundaries were determined by Xꢀray phase
analysis of airꢀannealed samples.
Xꢀray diffraction investigations were performed on
a Brukeraks D8 Advance automatic powder diffractoꢀ
meter (Cu
K irradiation, graphite monochromator,
α
maximal angle
per point) and an FRꢀ552 monochromator chamber
Cu irradiation, Ge internal standard). Unit cell
parameters were determined on a Guinier G670
HUBER automated diffractometer.
2
θ
= 90°, 0.01°–0.02° scan steps, 1 s
EXPERIMENTAL
Molybdates Ag2MoO4, MgMoO4, and Al2(MoO4)3
that were previously synthesized by the solidꢀphase
method, including the staged annealing of AgNO3
(pure for analysis grade), MgO (chemically pure
(
K
1
α
Differential thermal analysis was performed on an
MOM ODꢀ103 derivatograph (heating rate was
10 K/min, sample size was 0.3–0.4 g).
grade), Al(NO3)3 9H2O (pure for analysis grade) and
⋅
molybdenum trioxide (chemically pure grade) in a
stoichiometric ratio at 350–450°С (Ag2MoO4), 400–
750°С (MgMoO4), and 300–700°С (Al2(MoO4)3)
served as initial components. The Xꢀray diffraction
and thermal characteristics of the compounds
obtained agree satisfactorily with data in [6–8].
Table 1. Xꢀray diffraction characteristics of an Ag1 – xMg1 –
x
Al1 + x(MoO )3 variableꢀcomposition phase
4
Phase formation in the Ag2MoO4–MgMoO4–
Al2(MoO4)3 system was studied by the “intersecting
sections” method in the subsolidus region. The
MgMoO4–AgAl(MoO4)2 section, where intermediate
phases were formed, was studied over the entire concenꢀ
tration region in steps of 5–10 mol % and in the vicinity
of new compounds, in steps of 2.0–2.5 mol %. While
3
Compound
a
, Å
c
, Å
V, Å
AgMgAl(MoO4)3
9.2320(16) 22.800(4) 1682.9
Ag0.8Mg0.8Al1.2(MoO4)3 9.1870(13) 22.8046(19) 1666.9
Ag0.6Mg0.6Al1.4(MoO4)3 9.1430(16) 22.817(3) 1651.8
955

956
KOTOVA, KORSUN
Table 2. Indexing of Xꢀray diffraction pattern for AgMg3Al(MoO4)5
θexp deg I0 exp, Å h k l Δ( θexp – 2θtheor), deg θexp
2
,
I/
d
2
2
,
deg
I
/
I0
d
exp, Å
h k l
022, 50
Δ(
2θexp – 2θtheor), deg
10.052
13.164
15.084
5
8
1
8.793 020
6.720 001
5.869 030
–0.006
–0.006
+0.009
28.817
28.889
29.296
15 3.096
–0.037, +0.006
+0.004
1
4
2
3.088 141
3.046
+0.002
2
1
21
22
16.263
16.655
17.162
19.052
19.690
19.922
20.244
20.461
20.943
21.975
22.566
23.161
23.711
23.820
24.348
24.599
2
8
2
1
4
5.446
5.319
5.163
4.655
4.505
–0.003, +0.009
+0.003, +0.007
+0.005
29.570
30.052
30.464
30.588
30.694
31.164
31.668
31.954
32.081
32.438
32.778
32.859
32.955
33.227
33.341
33.687
33.812
34.170
34.341
34.734
35.100
35.299
35.671
35.761
36.191
36.378
36.520
36.693
37.013
37.187
37.700
37.847
37.847
38.458
13 3.019
2.971
+0.002
0
2
1, 120
5
–0.008, +0.036
–0.008, +0.033
–0.005
1
20, 01
1
230, 0
060, 2 3
1 3
30
2.868 032
3 2
11 2.932
12 2.920
1 1
1 2
1
1
1
+0.000
2
–0.018, +0.047
+0.003
2
1
8
1
2.910
–0.001
0
1
1
3
1,130
21
30, 101
2
28 4.453
4.383
–0.004
2
–0.027, +0.018
+0.007
2.823
2.799
–0.007, –0.003
–0.004
2
1
31, 201
32
<1 4.337 031
4.238 111
4
–0.005
16 2.788
–0.017, +0.018
+0.010
211, 21 1
17 4.042
60 3.937
<1 3.837
10 3.749
+0.003
2
1
9
2
9
9
2.758
2.730 151
2.723
2.716 160
1 3
1
1
5
1
+0.003
+0.007
1
1
0
2 1
–0.044
+0.000, +0.026
–0.010
31
0
4
2, 240
–0.002
4
1
3
3
3
3.733 140
3.653
3.616 041
–0.012
2.694
2.685
–0.007
2 4
1
–0.004
–0.007
1
40
2
2 1
+0.000
19 2.658
–0.005, +0.004
+0.012
2
40, 2 02
25.295 100 3.518 050
33 3.492 131
12 3.475
3.399 200
–0.008
5
3
7
9
3
2
1
1
9
2
2
2.649
2.622
2.609
2.581
2.555
2.541
2 1
1 6 1, 042
12
2 2
2
25.491
25.611
26.197
26.497
26.582
26.800
26.924
27.002
27.187
27.280
27.432
27.711
27.898
27.958
28.256
28.351
28.475
28.599
–0.003
–0.028, +0.007
+0.003
–0.002
1
41
2
2
+0.001
+0.001
2
63 3.361 002
42 3.351 210
–0.004
–0.010
1
2
3
3
2
–0.013
+0.000
1
24 3.324
–0.020, +0.013
+0.001
2.515 070
+0.019
0
1
2
1
2,
41
01
2 10
8
2
6
3.309
3.299
3.277
2.509
2.480
2.468
2.458
–0.016, –0.012
–0.005
2
0
22, 132
+0.010
5
2
–0.006, +0.041
–0.006
–0.005
012,
1
02
2 3
2 5
2
1
20 3.266
3.249
27 3.217
–0.017
2 1
1 1
1
3
+0.016
<1 2.447
–0.018
2
16 1
–0.003
<1 2.427 161
+0.025
2
11
3.195 220
3.189
3.156 150
3
3
8
8
5
9
–0.008
2
2.416
–0.001
2
0
2
50
1, 052
32, 170
–0.001
11 2.384
–0.025, +0.000
–0.025, +0.018
–0.018, +0.046
–0.010, +0.001
1
12
7
–0.005
1
1
4
2.375
2.375
2.339
3.145
3.132
3.119
+0.003
2
20
170, 2
70,
4
1
–0.006
2 2
1
1
1
52
–0.008, +0.000
14 1, 1 2 2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

PHASE FORMATION
957
Ag2MoO4
1:1
1:2
S1
S2
MgMoO4
Al2(MoO4)3
Diagram of subsolidus phase relations in the MgMoO –Ag Mg (MoO ) –AgAl(MoO ) –Al (MoO ) region for the
4
2
2
4 3
4 2
2
4 3
MgMoO –Ag MoO –Al (MoO ) system. S stands for Ag x Mg x Al x (MoO ) ; S stands for AgMg Al(MoO ) .
4
2
4
2
4 3
1
1 –
1 –
1 +
4 3
2
3
4 5
RESULTS AND DISCUSSION
points and points located inside the Ag2MoO4–
MgMoO4–Al2(MoO4) triangle showed that, in the
The Ag2MoO4–MgMoO4 and Ag2MoO4–
Al2(MoO4)3 systems were studied in [9–12], so we did
not additionally consider them.
solid phase at 500
MgMoO4–AgMg3Al(MoO4)5,
AgMg3Al(MoO4)5, Ag2Mg2(MoO4)3–AgAl(MoO4)2,
AgMg3Al(MoO4)5–Ag1 – xMg1 – xAl1 + x(MoO4)3, 0
0.4), Ag2Mg2(MoO4)3–Ag1–xMg1–xAl1+x(MoO4)3,
Ag1Ag1 xMg1 xAl1 x(MoO4)3–AgAl(MoO4)2,
°
С
, twoꢀphase sections are
Ag2Mg2(MoO4)3–
The
Ag2MoO4–MgMoO4 and
Ag2MoO4–
≤ ≤
x
Al2(MoO4)3 sides of the Ag2MoO4–MgMoO4–
Al2(MoO4)3 concentration triangle are characterized
by the formation of Ag2Mg2(MoO4)3 and AgAl(MoO4)2
double molybdates. Silver magnesium molybdate
Ag2Mg2(MoO4)3 belongs to the Na2Mg5(MoO4)6
structural family, at 500–530°С undergoes a reversible
polymorphic transformation, and melts incongruently
at 740°С. The homogeneity region expands towards
MgMoO4 to reach 2.0–2.5 mol % at 500°С [9]. Douꢀ
ble molybdate AgAl(MoO4)2 crystallizes in monoclinic
system (NaFe(MoO4)2 structural type), does not have
an appreciable homogeneity region and melts inconꢀ
gruently [10–12]. In view of the nonexistence of conꢀ
gruent compounds in the Ag2MoO4–Al2(MoO4)3
system [11], we confine the ternary salt system
investigation to the MgMoO4–Ag2Mg2(MoO4)3–
AgAl(MoO4)2–Al2(MoO4)3 region.
–
–
+
Ag1
Mg1 – xAl1 + x(MoO4)3–Al2(MoO4)3
,
and
⎯
x
AgMg3Al (MoO4)5–Al2(MoO4)3 (figure).
According to the Xꢀray powder diffraction data, the
AgMgAl(MoO4)3 and AgMg3Al(MoO4)5 triple molybꢀ
dates synthesized do not have an appreciable homogeꢀ
neity region along the AgAl(MoO4)2–MgMoO4 secꢀ
tion. An Ag1 – xMg1 – xAl1 + x(MoO4)3 variableꢀcomposiꢀ
tion phase is formed along the AgMgAl(MoO4)3–
Al2(MoO4)3 section and represents an AgMgAl(MoO4)3
based solid solution, whose singleꢀphase extent
reaches = 0.4. Al2(MoO4)3 weak reflections appear in
ꢀ
x
Xꢀray diffraction patterns at a higher concentration of
aluminum cations.
Xꢀray powder diffraction showed that the
We have not detected any phases on the MgMoO4– Ag1 xMg1 – xAl1 + x(MoO4)3 compounds are isostrucꢀ
⎯
Al2(MoO4)3 edge under our experimental conditions.
tural to sodium zinc scandium molybdate [13] with a
The Ag2Mg2(MoO4)3 and AgAl(MoO4)2 double
molybdates necessary for studying phase formation in
the Ag2MoO4–MgMoO4–Al2(MoO4)3 system, have
been synthesized by the solidꢀphase method from the
relevant neutral molybdates as described in [9–11].
3
rhombohedral lattice (space group R c, Z = 6) as to
reflection positions and intensity ratios. The homogeꢀ
neity extent was estimated from the change of lattice
parameters for the samples annealed at 500°С and
higher temperatures (Tables 1).
To investigate interactions in the Ag2MoO4–
MgMoO4–Al2(MoO4) system, we prepared a mixture
of neutral and double molybdates in the stoichiometꢀ
ric ratio, including the compositions of the intersecꢀ
tion points for all sections existing in the system. The group
results for the phase composition of the intersection ters:
AgMg3Al(MoO4)5
NaMg3In(MoO4)5, which has been synthesized by us
earlier [14] and indexed in triclinic system (space
is
isostructural
to
,
Z
= 2) with the following unit cell parameꢀ
P1
a
= 9.295(7) Å, = 17.619(2) Å, = 6.8570(7) Å,
b
c
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010

958
KOTOVA, KORSUN
4. V. K. Trunov, V. A. Efremov, and Yu. A. Velikodnyi, The
Crystal Chemistry and Properties of Double Molybdates
and Tungstates (Nauka, Leningrad, 1986) [in Russian].
α
= 87.420(9)°,
β
= 101.109(9)°, = 91.847(9)°, V =
γ
820.42 Å3, ρcalc = 4.078 g/cm3 (Table 2).
AgMgAl(MoO4)3 was found to melt incongruently
at 790°С, and AgMg3Al(MoO4)5 is thermally stable up
to 820°С; polymorphous transformations do not
occur.
In summary, the phase formation was studied in the
Ag2MoO4–MgMoO4–Al2(MoO4)3 system for the first
time. New triple molybdates AgMg3Al(MoO4)5 and
AgMgAl(MoO4)3 were synthesized, and the region of
AgMgAl(MoO4)3ꢀbased solid solutions was discovered.
Crystallographic and thermal characteristics were
determined for the compounds obtained. It has been
5. A. K. IvanovꢀShits and I. V. Murin, SolidꢀState Ionics
(S.ꢀPeterb. Gos. Univ., St. Petersburg, 2000) [in Rusꢀ
sian].
6. L. M. Plyasova and L. M. Kefeli, Izv. Akad. Nauk
SSSR, Neorg. Mater. 3 (5), 906 (1967).
7. V. V. Bakakin, R. F. Klevtsova, and L. A. Gaponenko,
Kristallografiya 27 (1), 38 (1982).
8. R. Kohlmuller and J.ꢀP. Faurie, Bull. Soc. Chim. Fr.,
No. 11, 4379 (1968).
9. G. D. Tsyrenova, S. F. Solodovnikov, E. G. Khaikina,
and E. T. Khobrakova, Zh. Neorg. Khim. 46 (12), 2066
(2001) [Russ. J. Inorg. Chem. 46 (12), 1886 (2001)].
established that the compounds Ag1 – xMg1 –
Al1 + x(MoO4)3 are of the NASICON structural type
x
10. JCPDS PDFꢀ2 Data base, Card # 56ꢀ0288.
3
(space group R c), which suggests a high ionic conꢀ
ductivity.
11. E. G. Khaikina, O. M. Basovich, and K. M. Khal’baeva,
Proceedings of the AllꢀRussia Scientific Conference on
Physicochemical Analysis (Makhachkala, 2007), p. 8 [in
Russian].
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 6 2010