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A magnetic study of UMO ternary mixed oxides (M: Mn, Fe, Co, Ni, Cu)
116
Journal of Alloys and Compounds, 193 (1993) 116--118 JALCOM 2114
A magnetic study of U-M-O ternary mixed oxides (M: Mn, Fe, Co, Ni, Cu) C. Miyake, T. Kondo, T. Takamiya and Y. Yoneda Department of Nuclear Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565 (Japan)
Abstract Ternary mixed oxides of MUaO~0 with a-UO3 type structure, M U 2 0 6 with hexagonal structure and fluorite structure, and CuUO4 were prepared. The magnetic susceptibility-temperature curves show a maximum in the temperature range of 4~43 K for all of them. The effective numbers of Bohr magneton for MUaO~0 correspond to the oxidation state of the 3d transition element in the individual mixed oxide, while the remaining mixed oxides show rather small value in spite of more than one ion being responsible for the magnetism. Electron spin resonance absorption signals were observed for all of them.
1. Introduction
3CuO + U3Os + 1/202 87o*c,air 3CuU04 200 h
Kemmler-Sack [1] performed an extensive study of the oxidation states of metallic ions in U - M - O ternary mixed oxides by magnetic susceptibility measurements at from room temperature to liquid nitrogen temperature. Bacmann and Bertaut [2] measured the magnetic susceptibility and neutron diffraction for several of these and found antiferromagnetic transitions. In this study, the magnetic susceptibility down to liquid helium temperature, electron spin resonance (ESR) absorption and infrared spectra are reported for nine of these ternary mixed oxides.
2.1. Materials
Nine samples for testing were prepared as follows and identified by powder X-ray diffraction analysis [3]. 900 *C, A r
Co304 q- 3U308 + 02 NiO + UO2 + UO3 NiO + U 3 0
8
900 °C, 0 2 100h
,ADU
400 *C, air, 8 h
+ Fe(OH)3
880 *C, 0 2 , 2 w e e k s
+U3Os (trace, 6N HNO3)
~FeU3Oao ' FeU30w
900 °C, 0 2
M n 0 2 + U308
300 h
' ~-Mn Us 01o
900 *C, A r
M n 0 2 + 2U02
240 h
) MnU206
291) h
3. Results and discussion
pellet, 900 °C, a i r 303 h
200 h
Magnetic susceptibility measurements were carried out with a Faraday type torsion magnetometer at from room temperature down to liquid helium temperature. ESR spectra were recorded with a JES-ME-2X at room temperature and liquid nitrogen temperature. In addition, the infrared spectra also were measured with Hitachi Perkin-Elmer 225 Grating Infrared Spectrophotometer.
' 3COU3 01o , NiU206
870 *C, air
CuO + U308 + 1/202
0925'8388/93/$6.00
, 3COU206
100 h
900 *C, A r - H 2
"~-1/202
ammonia water
+ Fe203 (in 6N HNO3)
2.2.Measurements
2. Experimental details
Co304 + U308 + 3UO 2
U308 (in 6N HNO3)
, NiU~01o
, CuUz01o
3.1. Magnetic susceptibilities
Figure 1 shows the magnetic susceptibility vs. temperature curves for MW3Oao (M." Mn, Fe, Co, Ni, Cu). In Figs. 2(a), 2(b) and 3(a), the dependences of magnetic susceptibility on temperature are shown for NiU206 and COU206 with a hexagonal structure, MnU206 with © 1993- Elsevier Sequoia. All fights reserved
C. Miyake et aL
o~
Magnetic study of U-M-O ternary mixed oxides
I
O
MU3OIo
-6 ~E420
- - o - - CoU3010
150 ...... :Mn
CO 0
: Fe
j m
.....
~100
........... : N i
E
CoU206 e.
:Co
-5 E "-
....... : C u
100
E .13 :~ ¢-i
117
E
u if}
\
50[
"":'.~..
-,....
.u_
' t6 o 6 b
un
40
NiU206
r En U .y
0 0
100
(a)
Temperature
200
(K)
0~
0
100 Temperature
200 (K)
Fig. 1. Dependence of magnetic susceptibility on temperature for MU3010 (M: Mn, Fe, Co, Ni, Cu).
a fluorite structure and CuU04 which has not yet been elucidated exactly, and compared with those of the corresponding MU3010 respectively. The magnetic parameters were obtained from the high temperature regions where the Curie-Weiss law holds, and their values are shown in Table 1. The effective numbers of Bohr magnetons for MU3Olo type correspond to the oxidation state of the 3d transition element in the individual mixed oxides, suggesting that uranium is hexavalent. This fact is consistent with the absorption due to the uranyl unit observed in infrared spectra. On the other hand, the effective numbers of Bohr magnetons for NiU206 and COU206 are rather smaller than those for MU3010 type. In the former mixed oxides, both the transition element ion and two U 5+ are responsible for paramagnetism, whereas in the latter only one transition element ion is paramagnetic. The temperature of Xm~ on magnetic susceptibility-temperature curves is a measure of the intensity of antiferromagnetic interactions. The fact that the temperatures of Xmaxfor NiU206, C o U 2 0 6 and MnU206 are higher than those for the corresponding MU3Ow suggests the contribution of pentavalent uranium to the antiferromagnetic interaction, leading to the reduction of magnetic susceptibility in the former mixed oxides in spite of more than one ion responsible for the magnetism.
3.2. ESR spectra In Fig. 3(b) the ESR spectra for CuUO4 and C u U 3 0 1 0 are shown as the representatives. In the crystal of
tO(
o --o- M n~010
x
E
300
..... MnU206 O
t~
20G
vU
E
50
(b)
100
Temperature
150
200
(K)
Fig. 2. (a) Dependence of magnetic susceptibility on temperature for NiU206 and COU206. (b) Dependence of magnetic susceptibility on temperature for MnU206.
CuUO4, copper ion is surrounded by six oxygen ions with a tetragonally distorted octahedral symmetry. The crystal structure of CuU3Olo has monoclinic or pseudohexagonal symmetry and is analogous to the structure of hexagonal a-UO3. Copper ion in this crystal is octahedrally surrounded as in the case of CuUO4, and is bonded more strongly to four oxygen atoms in the ab-plane than to the two oxygen atoms in the c-axis. Based on these crystal structures, the observed ESR spectra are explained as follows. Provided that the unpaired electron of Cu 2÷ is in dx:_y2 state, the parallel component of g-factor, g,, and perpendicular component, g i , are given as follows:
C. Miyake et aL / Magnetic study of U-M-O ternary mixed oxides
118
T A B L E 2. ESR parameters for mixed oxide, g-value and linewidth 15
CuU3010
% O
E
Mixed oxide
g-value
CuU04 CuU3Ot0
2.11 g, ~=2.393 g± = 2.065 gi~o=2.18
NiU206 NiU3Oto CoU206" CoU30,o FeU3010 MnU206 MnU30~0*
2.9 2.8 2.3
~cn 5 E
50
0
1 0
150
Temperature
(O)
2 0
(K )
3 1.9 2.5
Linewidth (gauss) 900
1025 1240 700 very broad 1500 1450 1190
*Observed at only room temperature.
CuU04
g : 2.11
~ " - ~
J ~
/,..~,. g~ = 2.065
Vo,, 0/2 (b)
~
= 2 393
0.'3 0.'4 Mognetic Field (']")
0.'5
Fig. 3. Dependence of magnetic susceptibility on temperature for CuUO4 and CuU3010. Co) E S R spectra for CuUO4 and CaU3Ot0.
T A B L E 1. Magnetic parameters for ternary oxides, effective n u m b e r of Bohr magnetons,/~en, temperature of maximum magnetic susceptibility, Tx=~, temperature-independent paramagnetic susceptibility, Xtip, and Weiss constant defined as X = C/(T-O) Ternary oxide
/~,~
Tx,~
Xt.i.p. ( x 10 -3)
Weiss constant
ot-UO3 CoU3Oto FeW3Oxo NiUaOlo CuU3010 /3-MnO3Ot0
4.3 5.55 2.80 1.75 4.5
10 43 13 18 4
0 1 0.18 0.4 0
- 1.4
hexagonal NiU206 COU206
2.34 4.0
38 33
1.24 1
- 3 - 0.4
0
+6
- 2 0 0
fluorite MnU206
5.0
CuU04
1.57
8 ~ 10 20 ~ 23
0.3
- 18
where ge is the g-factor for a free electron; and A is the spin-orbit coupling constant. Putting - 8 0 0 cm -1 for A of Cu 2÷ and the observed values of g, and g j_ at room temperature, the energy difference between d~y and dx~-y~, AE~y, and that between dye,= and dx~_~, AEy:.= are estimated to be 15 100 cm -1 and 21 100 cm-1 respectively. These values are consistent with the spectroscopic observation for Cu 2÷ complexes in the visible region. The g-values and the linewidths of the observed ESR spectra are given in Table 2. These g-values seem to correspond to each oxidation state in the mixed oxides.
Acknowledgments The authors wish to express their thanks to Professor Emeritus S. Imoto of Osaka University for his encouragement. This work is partially supported by the project of priority area for the physics on actinide compounds, a Grant-in-Aid No. 02 216 103 for Scientific Research from the Ministry of Education, Science and Culture.
References 1 S. Kemmler-Sack, Z. Anorg. AUg. Chem., 363 (1968) 295. 2 M. Bacmann and E. F. Bertaut, J. Phys. (Paris), 30 (1969) 949. 3 H. R. Hoekstra and R. H. Marshall, Lanthanide Actinide Chemistry No. 71, American Chemical Society, Washington, 1967. p. ~! 1.
Journal of Alloys and Compounds, 193 (1993) 116--118 JALCOM 2114
A magnetic study of U-M-O ternary mixed oxides (M: Mn, Fe, Co, Ni, Cu) C. Miyake, T. Kondo, T. Takamiya and Y. Yoneda Department of Nuclear Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565 (Japan)
Abstract Ternary mixed oxides of MUaO~0 with a-UO3 type structure, M U 2 0 6 with hexagonal structure and fluorite structure, and CuUO4 were prepared. The magnetic susceptibility-temperature curves show a maximum in the temperature range of 4~43 K for all of them. The effective numbers of Bohr magneton for MUaO~0 correspond to the oxidation state of the 3d transition element in the individual mixed oxide, while the remaining mixed oxides show rather small value in spite of more than one ion being responsible for the magnetism. Electron spin resonance absorption signals were observed for all of them.
1. Introduction
3CuO + U3Os + 1/202 87o*c,air 3CuU04 200 h
Kemmler-Sack [1] performed an extensive study of the oxidation states of metallic ions in U - M - O ternary mixed oxides by magnetic susceptibility measurements at from room temperature to liquid nitrogen temperature. Bacmann and Bertaut [2] measured the magnetic susceptibility and neutron diffraction for several of these and found antiferromagnetic transitions. In this study, the magnetic susceptibility down to liquid helium temperature, electron spin resonance (ESR) absorption and infrared spectra are reported for nine of these ternary mixed oxides.
2.1. Materials
Nine samples for testing were prepared as follows and identified by powder X-ray diffraction analysis [3]. 900 *C, A r
Co304 q- 3U308 + 02 NiO + UO2 + UO3 NiO + U 3 0
8
900 °C, 0 2 100h
,ADU
400 *C, air, 8 h
+ Fe(OH)3
880 *C, 0 2 , 2 w e e k s
+U3Os (trace, 6N HNO3)
~FeU3Oao ' FeU30w
900 °C, 0 2
M n 0 2 + U308
300 h
' ~-Mn Us 01o
900 *C, A r
M n 0 2 + 2U02
240 h
) MnU206
291) h
3. Results and discussion
pellet, 900 °C, a i r 303 h
200 h
Magnetic susceptibility measurements were carried out with a Faraday type torsion magnetometer at from room temperature down to liquid helium temperature. ESR spectra were recorded with a JES-ME-2X at room temperature and liquid nitrogen temperature. In addition, the infrared spectra also were measured with Hitachi Perkin-Elmer 225 Grating Infrared Spectrophotometer.
' 3COU3 01o , NiU206
870 *C, air
CuO + U308 + 1/202
0925'8388/93/$6.00
, 3COU206
100 h
900 *C, A r - H 2
"~-1/202
ammonia water
+ Fe203 (in 6N HNO3)
2.2.Measurements
2. Experimental details
Co304 + U308 + 3UO 2
U308 (in 6N HNO3)
, NiU~01o
, CuUz01o
3.1. Magnetic susceptibilities
Figure 1 shows the magnetic susceptibility vs. temperature curves for MW3Oao (M." Mn, Fe, Co, Ni, Cu). In Figs. 2(a), 2(b) and 3(a), the dependences of magnetic susceptibility on temperature are shown for NiU206 and COU206 with a hexagonal structure, MnU206 with © 1993- Elsevier Sequoia. All fights reserved
C. Miyake et aL
o~
Magnetic study of U-M-O ternary mixed oxides
I
O
MU3OIo
-6 ~E420
- - o - - CoU3010
150 ...... :Mn
CO 0
: Fe
j m
.....
~100
........... : N i
E
CoU206 e.
:Co
-5 E "-
....... : C u
100
E .13 :~ ¢-i
117
E
u if}
\
50[
"":'.~..
-,....
.u_
' t6 o 6 b
un
40
NiU206
r En U .y
0 0
100
(a)
Temperature
200
(K)
0~
0
100 Temperature
200 (K)
Fig. 1. Dependence of magnetic susceptibility on temperature for MU3010 (M: Mn, Fe, Co, Ni, Cu).
a fluorite structure and CuU04 which has not yet been elucidated exactly, and compared with those of the corresponding MU3010 respectively. The magnetic parameters were obtained from the high temperature regions where the Curie-Weiss law holds, and their values are shown in Table 1. The effective numbers of Bohr magnetons for MU3Olo type correspond to the oxidation state of the 3d transition element in the individual mixed oxides, suggesting that uranium is hexavalent. This fact is consistent with the absorption due to the uranyl unit observed in infrared spectra. On the other hand, the effective numbers of Bohr magnetons for NiU206 and COU206 are rather smaller than those for MU3010 type. In the former mixed oxides, both the transition element ion and two U 5+ are responsible for paramagnetism, whereas in the latter only one transition element ion is paramagnetic. The temperature of Xm~ on magnetic susceptibility-temperature curves is a measure of the intensity of antiferromagnetic interactions. The fact that the temperatures of Xmaxfor NiU206, C o U 2 0 6 and MnU206 are higher than those for the corresponding MU3Ow suggests the contribution of pentavalent uranium to the antiferromagnetic interaction, leading to the reduction of magnetic susceptibility in the former mixed oxides in spite of more than one ion responsible for the magnetism.
3.2. ESR spectra In Fig. 3(b) the ESR spectra for CuUO4 and C u U 3 0 1 0 are shown as the representatives. In the crystal of
tO(
o --o- M n~010
x
E
300
..... MnU206 O
t~
20G
vU
E
50
(b)
100
Temperature
150
200
(K)
Fig. 2. (a) Dependence of magnetic susceptibility on temperature for NiU206 and COU206. (b) Dependence of magnetic susceptibility on temperature for MnU206.
CuUO4, copper ion is surrounded by six oxygen ions with a tetragonally distorted octahedral symmetry. The crystal structure of CuU3Olo has monoclinic or pseudohexagonal symmetry and is analogous to the structure of hexagonal a-UO3. Copper ion in this crystal is octahedrally surrounded as in the case of CuUO4, and is bonded more strongly to four oxygen atoms in the ab-plane than to the two oxygen atoms in the c-axis. Based on these crystal structures, the observed ESR spectra are explained as follows. Provided that the unpaired electron of Cu 2÷ is in dx:_y2 state, the parallel component of g-factor, g,, and perpendicular component, g i , are given as follows:
C. Miyake et aL / Magnetic study of U-M-O ternary mixed oxides
118
T A B L E 2. ESR parameters for mixed oxide, g-value and linewidth 15
CuU3010
% O
E
Mixed oxide
g-value
CuU04 CuU3Ot0
2.11 g, ~=2.393 g± = 2.065 gi~o=2.18
NiU206 NiU3Oto CoU206" CoU30,o FeU3010 MnU206 MnU30~0*
2.9 2.8 2.3
~cn 5 E
50
0
1 0
150
Temperature
(O)
2 0
(K )
3 1.9 2.5
Linewidth (gauss) 900
1025 1240 700 very broad 1500 1450 1190
*Observed at only room temperature.
CuU04
g : 2.11
~ " - ~
J ~
/,..~,. g~ = 2.065
Vo,, 0/2 (b)
~
= 2 393
0.'3 0.'4 Mognetic Field (']")
0.'5
Fig. 3. Dependence of magnetic susceptibility on temperature for CuUO4 and CuU3010. Co) E S R spectra for CuUO4 and CaU3Ot0.
T A B L E 1. Magnetic parameters for ternary oxides, effective n u m b e r of Bohr magnetons,/~en, temperature of maximum magnetic susceptibility, Tx=~, temperature-independent paramagnetic susceptibility, Xtip, and Weiss constant defined as X = C/(T-O) Ternary oxide
/~,~
Tx,~
Xt.i.p. ( x 10 -3)
Weiss constant
ot-UO3 CoU3Oto FeW3Oxo NiUaOlo CuU3010 /3-MnO3Ot0
4.3 5.55 2.80 1.75 4.5
10 43 13 18 4
0 1 0.18 0.4 0
- 1.4
hexagonal NiU206 COU206
2.34 4.0
38 33
1.24 1
- 3 - 0.4
0
+6
- 2 0 0
fluorite MnU206
5.0
CuU04
1.57
8 ~ 10 20 ~ 23
0.3
- 18
where ge is the g-factor for a free electron; and A is the spin-orbit coupling constant. Putting - 8 0 0 cm -1 for A of Cu 2÷ and the observed values of g, and g j_ at room temperature, the energy difference between d~y and dx~-y~, AE~y, and that between dye,= and dx~_~, AEy:.= are estimated to be 15 100 cm -1 and 21 100 cm-1 respectively. These values are consistent with the spectroscopic observation for Cu 2÷ complexes in the visible region. The g-values and the linewidths of the observed ESR spectra are given in Table 2. These g-values seem to correspond to each oxidation state in the mixed oxides.
Acknowledgments The authors wish to express their thanks to Professor Emeritus S. Imoto of Osaka University for his encouragement. This work is partially supported by the project of priority area for the physics on actinide compounds, a Grant-in-Aid No. 02 216 103 for Scientific Research from the Ministry of Education, Science and Culture.
References 1 S. Kemmler-Sack, Z. Anorg. AUg. Chem., 363 (1968) 295. 2 M. Bacmann and E. F. Bertaut, J. Phys. (Paris), 30 (1969) 949. 3 H. R. Hoekstra and R. H. Marshall, Lanthanide Actinide Chemistry No. 71, American Chemical Society, Washington, 1967. p. ~! 1.