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Phases of scheelite structure in the neptunium molybdate and sodium or lithium molybdate systems
J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2797-2801. Pergamon Press.
Printed in Great Britain
PHASES OF SCHEELITE STRUCTURE IN THE NEPTUNIUM MOLYBDATE AND SODIUM OR LITHIUM MOLYBDATE SYSTEMS M O N I Q U E PAGES lnstitut du Radium, Laboratoire Curie, I 1, rue P. et M. Curie, 75 Paris V, France and W. F R E U N D L I C H Laboratoire de Chimie Min6rale, ER 9 CNRS. 1, rue Victor-Cousin, 75 Paris V, France (Received 1 July 1971) Abstract-The establishment of solid-liquid equilibrium diagrams for the systems Np(MoO4)zNa2MoO4 and Np(MoO4h-Li2MoO4, coupled with solid-state studies by X-ray diffraction, has led to the discovery of three new phases: Na2Np(MoO4)3 with scheelite structure, and Na4Np(MoO4)4 and Li4Np(MoO4)4 with a scheelite superstructure. Congruent fusion occurs only with the lithium compound (m.p. = 647°C). No phase corresponding to Li4NpMoO4 is observed for thorium, whereas the sodium compounds of Np and Th are isostructural.
INTRODUCTION
IN SCHEELITE, C a W O 4 , the calcium can be replaced by various elements, and particularly by trivalent ions of the lanthanides. These can be vacancy substitutions or can be compensated by monovalent ions; i.e. 3Ca~+ = 2Ln3+ + [] or 2Ca2+ = Ln3+ + M +. For example, we have demonstrated the existence of a tungstate and a molybdate of americium(III), Am~(MO4)8, (where M = W or Mo) with scheelite structure [1]. These can be considered as limiting cases of vacancy substitution, according to Ca 12+ Am3+l--1 MO., -3x 2x 3" 4
with x = k.
In addition, the tungstates NaLn(WO4)2, (where Ln = Nd, Sm, Y), with scheelite structure are also known [2]. The complete substitution of calcium by monovalent and tetravalent ions is also possible, since the compound Na2Th(MoO4)a is known[3], with 3Ca 2+ = 2 M + + A 4+. In certain cases, a superstructure is observed; e.g. NasLnm(WO4)4 [4], Na4Th(WO4)4 and Na2Th(WO 4)3 [3]. The present work concerns attempts to obtain complete compensated substitution of calcium by the transuranium element neptunium, in the oxidation state 1. 2. 3. 4.
W. Freundlich and M. Pag6s, C. r. Acad. S ci. Paris 7~9C, 392 (1969). L. M. Kovba, I. A. Murav'eva, V. K. Tmnov and V. I. Spicyn, Dan S S S R , 175, 1290 0967). V. K. Trunov and N. N. Busnev, Radiokhimija l l , 2, 245 (1969). L. R. Sill6n and H. Sundvall, Ark. Kemi Mineral. Geol. 17A, l0 (1943). 2797
M O N I Q U E PAGI~S and W. F R E U N D L 1 C H
2798
IV. We have studied the solid-state reactions of the molybdate of Np xv with the molybdates of Na and Li. The solid-liquid equilibrium diagrams have been established and the crystalline phases formed have been identified. EXPERIMENTAL Reactions were, in general, carried out by prolonged heating of various mixtures between 500 ° and 600°C, in closed platinum crucibles. The molybdate of Np w, however, was prepared at 700°C from the oxides MoO3 and NpO2[1]. Sodium and lithium molybdates were obtained by reaction of the respective alkaline carbonates with MOO3. Thermal analysis was carried out by means of a differential micro-analyser with hollow thermocouples in which the closed platinum crucibles were placed (capacity 6/zl). The sensitivity of the apparatus was such that milligram samples could be used. The equilibrium diagrams were established by means of heating curves (speed, 3-6°/min); the reverse procedure gave, in general, appreciable supercooling. The phases, were identified by X-ray diffraction [4], using a "Guinier de Wolff" camera. RESULTS AND DISCUSSION
The NazMoO4-Np(MoO4)2 system
With this system, two quaternary phases were found: Na4Np(MoO4)4 and Na2Np(MoO4)3. The solid-liquid equilibrium diagram (Fig. 1) shows three invariants: a eutectic and two peritectics. Eutectic E
Peritectic P1
Peritectic/'2
538
704
736
9
32
49
Temp. (°C) mole% Np(MoO4)2
/ t/
IOOC
/ ~
Liq.
[M00412 + Liq.
80C P ~:~':ff;Liq.-
P
"
-
~--O-Q
......
E
No~doO4 + I
400
r
r 20
I
i
.~ J _ .-i...e-- - Q.. . . . . . . . .
"r.Tr
IT, NplMo04I
~ 40
I 60
I
I 80
I
lI
Fig. 1. Solid-liquid equilibrium diagram for the Na2MoO4-Np(MoO4)2 system.
Phases of scheelite structure
2799
The two compounds are characterized by non-congruent melting and exhibit a reversible polymorphic transformation at 580 ° and 500°C respectively. It was not possible to conserve the metastable "high-temperature" forms, even by rapid cooling in liquid nitrogen. Na4Np(MoO4)4
The X-ray diffraction pattern of this phase is analogous to that of Na4Th It is a tetragonal phase (Table 1), with the following parameters: a = 11.240 ~ , c = 11.800 A. This molybdate shows a superstructure: the parameter a of the elementary cell is about twice that of scheelite. (M004)4.
Table 1. X-ray data for Na4Np(MoO4)4 do~
dcalc
dobs
dealt
h
k
l
(A)
(A)
/re,
h
k
l
(m)
(m)
lrel
1 2 2 1 3 2 3 3 0 3 4 2 4 3
0 0 1 0 0 1 1 2 0 0 1 0 2 2
1 0 1 3 1 3 2 1 4 3 1 4 0 3
8.15 5.62 4.62 3.72 3.57 3-097 3.049 3"01 2,950 2.712 2.652 2.612 2"512 2.442
8.145 5.620 4.625 3.715 3.571 3.099 3.045 3,013 2.950 2.715 2.657 2.614 2.513 2.443
vs vw m w m vw vs vw w w vw vw m m
4 4 5 5 4 4 4 3 6 6 3 6 5 7
2 1 0 2 4 3 2 2 1 2 1 3 4 2
2 3 1 1 0 3 4 5 1 0 6 0 3 1
2.310 2.241 2.205 2-056 2.000 1-951 1.912 1.882 1.828 1.777 1-720 1-674 1.604 1.532
2-312 2.243 2.208 2.055 1.987 1.951 1.913 1-882 1-827 1.778 1.721 1.675 1.603 1.532
vw vw vw w w w m w w w w w w m
NazNp(MoO4)3 This compound and Na2Th(MoO4)3 are isostructural. Its powder diagram can be indexed as a tetragonal phase with the parameters (Table 2); a = 5.244 ,~, c = 11.420A. It may be noted that the phases Na4MW(MoO4)4 and NazM tv (MOO4)3 are isostructural for Np and Th. Table 2. X-ray data for NazNp(MoO4)3 dob~
dcal~
dob,
d~l~
h
k
l
~A)
(A)
/roi
h
k
1
(A)
(A)
1 1 0 2 2 1 2 2 2
0 1 0 0 1 1 I 0 2
1 2 4 0 1 4 3 4 0
4.72 3" 10 2.85 2-61 2.31 2.26 1.98 1.927 1-844
4.75 3-102 2-855 2-612 2-290 2-260 1-990 1-926 1-847
m vs m m vw vw vw s m
1 2 3 2 4 3 4 4 4
1 1 1 2 0 1 1 0 2
6 5 2 4 0 6 3 4 0
1.690 1.632 1.585 1'549 1.304 1.247 1.201 1.184 I. 165
1.692 1'635 1.588 1'550 1.306 1.248 1-202 1.187 1' 168
5. M. Pages and W. Freundlich, C, r. A cad, Sci. Paris 268C, 2181 (1969).
lro~ rn vw m w vw m vw vw vw
2800
MONIQUE
PAGI~S and W. F R E U N D L I C H
The Li2MoO4-Np(MoO4)2system A ternary phase, Li4Np(MoO4)4, has been observed. The solid-liquid equilibrium diagram (Fig. 2) shows two invariants, the eutectics E1 and E~:
T e m p . (°C) mole% Np(MoO4)~
620
635
17
67.5
8oc,I P~_.70£ 600
/ /Np(MoO,)z*Liq
Liq. ~
a=. ;'El
"
-
I
20
~ /
LizMOO4
"E2
-
Li2÷M°041I 500
Fig. 2.
I I I
•
I+ Np(M°04)2 I 60
4 0
80
I Li4NP(Mo04)41 I
mot *~
Solid-liquidequilibriumdiagram for the
Np(Mo04)z
Li2MoO4-Np(MoO4)2
system.
Table 3. X-ray data for Li4Np(MoOa)4
dob~
d~o
do~,
d~l~
h
k
l
(A)
(,~)
1,~]
h
k
l
(~)
(A)
lr~,
1 2 2 2 2 3 1 3 3 2 4 0 4 3 4 2 2
0 0 1 2 0 0 0 2 1 1 1 0 1 0 2 0 1
I 0 1 0 2 1 3 1 2 3 0 4 1 3 0 4 4
7.69 5.55 4.50 3.93 3.84 3.50 3.38 2.964 2.930 2-885 2'700 2.662 2'612 2'561 2"485 2-402 2.348
7.686 5.552 4.501 3"926 3.843 3"496 3.381 2.959 2"931 2.888 2-693 2.662 2'6i 1 2-562 2.483 2"400 2.346
vs w s vw w m m w vs w m w m vw m w w
3 4 5 4 3 5 5 4 2 5 4 3 6 5 6 5 5
2 2 0 1 1 2 1 4 1 2 3 0 1 2 2 4 2
3 2 1 3 4 1 2 0 5 2 3 5 1 3 0 1 4
2.328 2.254 2.174 2' 144 2'12 2"025 2.017 1.963 1.957 1 "922 1.881 1 '846 1.800 1.785 1 "757 1"711 1 '632
2.326 2.250 2.174 2' 146 2-121 2.024 2.016 1.963 1.957 1 "923 1.883 1.846 1.799 1"783 1.756 1"712 1.630
w w vw vw vw w w vw w w w w w w m w m
2801
Phases of scheelite structure Table 4 Parameters Phase
a (A)
c (,~)
c/a
Structure
Na4Th(MoO4)4
11.39
11.94
1.048
Na4Np(MoO4)4
11.240
11.800
1.050
NazTh(MoO4)3 Na2Np(MoO4)3 Li4Np(MoO4)4
5.293 5.224 11.105
11.580 11.420 10.648
2.188 2.186 0.959
Superstructure scheelite [3] Superstructure scheelite Scheelite[3] Scheelite Superstructure scheelite
The compound is characterized by congruent melting (m.p. = 647°C). Being isostructural with Na4Np(MoO4)4, its powder diagram can be indexed as a tetragonal phase, with a = 11.105 A, c = 10.698 A. It may be noted that no compound corresponding to Li4Np(MoO4)4 exists for the lithium-thorium molybdate system. On the other hand, the formation of a cubic phase, Li2(MoOD4ThMo2Os, has been reported[3]. One thus finds an interesting difference, in this case, between the cations Np 4+ and Th 4+. The crystallographic data for the different scheelite-type phases reported in this paper are collected in Table 4.
Printed in Great Britain
PHASES OF SCHEELITE STRUCTURE IN THE NEPTUNIUM MOLYBDATE AND SODIUM OR LITHIUM MOLYBDATE SYSTEMS M O N I Q U E PAGES lnstitut du Radium, Laboratoire Curie, I 1, rue P. et M. Curie, 75 Paris V, France and W. F R E U N D L I C H Laboratoire de Chimie Min6rale, ER 9 CNRS. 1, rue Victor-Cousin, 75 Paris V, France (Received 1 July 1971) Abstract-The establishment of solid-liquid equilibrium diagrams for the systems Np(MoO4)zNa2MoO4 and Np(MoO4h-Li2MoO4, coupled with solid-state studies by X-ray diffraction, has led to the discovery of three new phases: Na2Np(MoO4)3 with scheelite structure, and Na4Np(MoO4)4 and Li4Np(MoO4)4 with a scheelite superstructure. Congruent fusion occurs only with the lithium compound (m.p. = 647°C). No phase corresponding to Li4NpMoO4 is observed for thorium, whereas the sodium compounds of Np and Th are isostructural.
INTRODUCTION
IN SCHEELITE, C a W O 4 , the calcium can be replaced by various elements, and particularly by trivalent ions of the lanthanides. These can be vacancy substitutions or can be compensated by monovalent ions; i.e. 3Ca~+ = 2Ln3+ + [] or 2Ca2+ = Ln3+ + M +. For example, we have demonstrated the existence of a tungstate and a molybdate of americium(III), Am~(MO4)8, (where M = W or Mo) with scheelite structure [1]. These can be considered as limiting cases of vacancy substitution, according to Ca 12+ Am3+l--1 MO., -3x 2x 3" 4
with x = k.
In addition, the tungstates NaLn(WO4)2, (where Ln = Nd, Sm, Y), with scheelite structure are also known [2]. The complete substitution of calcium by monovalent and tetravalent ions is also possible, since the compound Na2Th(MoO4)a is known[3], with 3Ca 2+ = 2 M + + A 4+. In certain cases, a superstructure is observed; e.g. NasLnm(WO4)4 [4], Na4Th(WO4)4 and Na2Th(WO 4)3 [3]. The present work concerns attempts to obtain complete compensated substitution of calcium by the transuranium element neptunium, in the oxidation state 1. 2. 3. 4.
W. Freundlich and M. Pag6s, C. r. Acad. S ci. Paris 7~9C, 392 (1969). L. M. Kovba, I. A. Murav'eva, V. K. Tmnov and V. I. Spicyn, Dan S S S R , 175, 1290 0967). V. K. Trunov and N. N. Busnev, Radiokhimija l l , 2, 245 (1969). L. R. Sill6n and H. Sundvall, Ark. Kemi Mineral. Geol. 17A, l0 (1943). 2797
M O N I Q U E PAGI~S and W. F R E U N D L 1 C H
2798
IV. We have studied the solid-state reactions of the molybdate of Np xv with the molybdates of Na and Li. The solid-liquid equilibrium diagrams have been established and the crystalline phases formed have been identified. EXPERIMENTAL Reactions were, in general, carried out by prolonged heating of various mixtures between 500 ° and 600°C, in closed platinum crucibles. The molybdate of Np w, however, was prepared at 700°C from the oxides MoO3 and NpO2[1]. Sodium and lithium molybdates were obtained by reaction of the respective alkaline carbonates with MOO3. Thermal analysis was carried out by means of a differential micro-analyser with hollow thermocouples in which the closed platinum crucibles were placed (capacity 6/zl). The sensitivity of the apparatus was such that milligram samples could be used. The equilibrium diagrams were established by means of heating curves (speed, 3-6°/min); the reverse procedure gave, in general, appreciable supercooling. The phases, were identified by X-ray diffraction [4], using a "Guinier de Wolff" camera. RESULTS AND DISCUSSION
The NazMoO4-Np(MoO4)2 system
With this system, two quaternary phases were found: Na4Np(MoO4)4 and Na2Np(MoO4)3. The solid-liquid equilibrium diagram (Fig. 1) shows three invariants: a eutectic and two peritectics. Eutectic E
Peritectic P1
Peritectic/'2
538
704
736
9
32
49
Temp. (°C) mole% Np(MoO4)2
/ t/
IOOC
/ ~
Liq.
[M00412 + Liq.
80C P ~:~':ff;Liq.-
P
"
-
~--O-Q
......
E
No~doO4 + I
400
r
r 20
I
i
.~ J _ .-i...e-- - Q.. . . . . . . . .
"r.Tr
IT, NplMo04I
~ 40
I 60
I
I 80
I
lI
Fig. 1. Solid-liquid equilibrium diagram for the Na2MoO4-Np(MoO4)2 system.
Phases of scheelite structure
2799
The two compounds are characterized by non-congruent melting and exhibit a reversible polymorphic transformation at 580 ° and 500°C respectively. It was not possible to conserve the metastable "high-temperature" forms, even by rapid cooling in liquid nitrogen. Na4Np(MoO4)4
The X-ray diffraction pattern of this phase is analogous to that of Na4Th It is a tetragonal phase (Table 1), with the following parameters: a = 11.240 ~ , c = 11.800 A. This molybdate shows a superstructure: the parameter a of the elementary cell is about twice that of scheelite. (M004)4.
Table 1. X-ray data for Na4Np(MoO4)4 do~
dcalc
dobs
dealt
h
k
l
(A)
(A)
/re,
h
k
l
(m)
(m)
lrel
1 2 2 1 3 2 3 3 0 3 4 2 4 3
0 0 1 0 0 1 1 2 0 0 1 0 2 2
1 0 1 3 1 3 2 1 4 3 1 4 0 3
8.15 5.62 4.62 3.72 3.57 3-097 3.049 3"01 2,950 2.712 2.652 2.612 2"512 2.442
8.145 5.620 4.625 3.715 3.571 3.099 3.045 3,013 2.950 2.715 2.657 2.614 2.513 2.443
vs vw m w m vw vs vw w w vw vw m m
4 4 5 5 4 4 4 3 6 6 3 6 5 7
2 1 0 2 4 3 2 2 1 2 1 3 4 2
2 3 1 1 0 3 4 5 1 0 6 0 3 1
2.310 2.241 2.205 2-056 2.000 1-951 1.912 1.882 1.828 1.777 1-720 1-674 1.604 1.532
2-312 2.243 2.208 2.055 1.987 1.951 1.913 1-882 1-827 1.778 1.721 1.675 1.603 1.532
vw vw vw w w w m w w w w w w m
NazNp(MoO4)3 This compound and Na2Th(MoO4)3 are isostructural. Its powder diagram can be indexed as a tetragonal phase with the parameters (Table 2); a = 5.244 ,~, c = 11.420A. It may be noted that the phases Na4MW(MoO4)4 and NazM tv (MOO4)3 are isostructural for Np and Th. Table 2. X-ray data for NazNp(MoO4)3 dob~
dcal~
dob,
d~l~
h
k
l
~A)
(A)
/roi
h
k
1
(A)
(A)
1 1 0 2 2 1 2 2 2
0 1 0 0 1 1 I 0 2
1 2 4 0 1 4 3 4 0
4.72 3" 10 2.85 2-61 2.31 2.26 1.98 1.927 1-844
4.75 3-102 2-855 2-612 2-290 2-260 1-990 1-926 1-847
m vs m m vw vw vw s m
1 2 3 2 4 3 4 4 4
1 1 1 2 0 1 1 0 2
6 5 2 4 0 6 3 4 0
1.690 1.632 1.585 1'549 1.304 1.247 1.201 1.184 I. 165
1.692 1'635 1.588 1'550 1.306 1.248 1-202 1.187 1' 168
5. M. Pages and W. Freundlich, C, r. A cad, Sci. Paris 268C, 2181 (1969).
lro~ rn vw m w vw m vw vw vw
2800
MONIQUE
PAGI~S and W. F R E U N D L I C H
The Li2MoO4-Np(MoO4)2system A ternary phase, Li4Np(MoO4)4, has been observed. The solid-liquid equilibrium diagram (Fig. 2) shows two invariants, the eutectics E1 and E~:
T e m p . (°C) mole% Np(MoO4)~
620
635
17
67.5
8oc,I P~_.70£ 600
/ /Np(MoO,)z*Liq
Liq. ~
a=. ;'El
"
-
I
20
~ /
LizMOO4
"E2
-
Li2÷M°041I 500
Fig. 2.
I I I
•
I+ Np(M°04)2 I 60
4 0
80
I Li4NP(Mo04)41 I
mot *~
Solid-liquidequilibriumdiagram for the
Np(Mo04)z
Li2MoO4-Np(MoO4)2
system.
Table 3. X-ray data for Li4Np(MoOa)4
dob~
d~o
do~,
d~l~
h
k
l
(A)
(,~)
1,~]
h
k
l
(~)
(A)
lr~,
1 2 2 2 2 3 1 3 3 2 4 0 4 3 4 2 2
0 0 1 2 0 0 0 2 1 1 1 0 1 0 2 0 1
I 0 1 0 2 1 3 1 2 3 0 4 1 3 0 4 4
7.69 5.55 4.50 3.93 3.84 3.50 3.38 2.964 2.930 2-885 2'700 2.662 2'612 2'561 2"485 2-402 2.348
7.686 5.552 4.501 3"926 3.843 3"496 3.381 2.959 2"931 2.888 2-693 2.662 2'6i 1 2-562 2.483 2"400 2.346
vs w s vw w m m w vs w m w m vw m w w
3 4 5 4 3 5 5 4 2 5 4 3 6 5 6 5 5
2 2 0 1 1 2 1 4 1 2 3 0 1 2 2 4 2
3 2 1 3 4 1 2 0 5 2 3 5 1 3 0 1 4
2.328 2.254 2.174 2' 144 2'12 2"025 2.017 1.963 1.957 1 "922 1.881 1 '846 1.800 1.785 1 "757 1"711 1 '632
2.326 2.250 2.174 2' 146 2-121 2.024 2.016 1.963 1.957 1 "923 1.883 1.846 1.799 1"783 1.756 1"712 1.630
w w vw vw vw w w vw w w w w w w m w m
2801
Phases of scheelite structure Table 4 Parameters Phase
a (A)
c (,~)
c/a
Structure
Na4Th(MoO4)4
11.39
11.94
1.048
Na4Np(MoO4)4
11.240
11.800
1.050
NazTh(MoO4)3 Na2Np(MoO4)3 Li4Np(MoO4)4
5.293 5.224 11.105
11.580 11.420 10.648
2.188 2.186 0.959
Superstructure scheelite [3] Superstructure scheelite Scheelite[3] Scheelite Superstructure scheelite
The compound is characterized by congruent melting (m.p. = 647°C). Being isostructural with Na4Np(MoO4)4, its powder diagram can be indexed as a tetragonal phase, with a = 11.105 A, c = 10.698 A. It may be noted that no compound corresponding to Li4Np(MoO4)4 exists for the lithium-thorium molybdate system. On the other hand, the formation of a cubic phase, Li2(MoOD4ThMo2Os, has been reported[3]. One thus finds an interesting difference, in this case, between the cations Np 4+ and Th 4+. The crystallographic data for the different scheelite-type phases reported in this paper are collected in Table 4.