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Formation of the Cu3Au type solid solution of UPd3 by doping a small amount of URu3
L
Journal of Alloys and Compounds 274 (1998) 222–228
Formation of the Cu 3 Au type solid solution of UPd 3 by doping a small amount of URu 3 Ken Kurosaki*, Masayoshi Uno Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, Yamadaoka 2 -1, Suita, Osaka 565 -0781, Japan Received 24 November 1997; received in revised form 21 March 1998
Abstract In order to investigate the formation of the Cu 3 Au type UPd 3 solid solution, reactions of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out. Two Cu 3 Au type compounds were obtained, one was a solid solution of URu 3 with a small amount of UPd 3 , and the other was a solid solution of UPd 3 with a small amount of URu 3 . Although pure UPd 3 has a hexagonal TiNi 3 type structure, a solid solution of UPd 3 with a Cu 3 Au type structure can be obtained when it contains URu 3 in the region of 12–14%. 1998 Elsevier Science S.A. Keywords: Uranium; Platinum-family metals; Solid solution; UPd 3 ; Cu 3 Au type structure
1. Introduction Platinum-family metal fission products (FP) have large fission yield in a nuclear reactor. In oxide fuel, platinumfamily metal FPs (Me: Ru, Rh, Pd) form mainly intermetallic compounds with other transition metal FPs and do not react with UO 2 , but in nitride fuel, platinum-family metals react with UN and form intermetallic compounds of the type UMe 3 . We have investigated the reaction behaviors between UN and Me because FPs may provide a large influence on the physical and chemical properties of the fuel. Although several studies on the binary phase diagrams for U–Me systems have been made [1,2], the ternary and quaternary phase diagrams are not reported. The crystal structures and the lattice parameters of UMe 3 type intermetallic compounds are summarized in Table 1. In the previous work for the pseudo-binary system [5], it was found that the reactions between UN and Ru, and between UN and Rh produced URu 3 and URh 3 as intermetallic compounds, respectively. In the reactions between UN and Pd, UPd 4 (U: 18|20%) was formed in addition to UPd 3 . *Corresponding author. Tel.: 181 6 8797906; fax: 181 6 8797889; e-mail: [email protected] 0925-8388 / 98 / $19.00 1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 98 )00544-1
The reactions of UN13 (Ru x 1Rh y 1Pd 12x 2y ), [0] # (x,y)] # 1] at 1673 K under vacuum (|10 22 Pa) for the pseudo-ternary and quaternary systems were carried out [6]. These results are redrawn in Fig. 1. The reactions between UN, Ru and Rh, and between UN, Rh and Pd produced a Cu 3 Au type solid solution. However, two compounds were obtained in the reactions between UN, Ru and Pd at any Pd ratio in the pseudo-ternary system, and between UN, Ru, Rh and Pd at the molar ratio of Ru:Rh:Pd51:1:4 in the pseudo-quaternary system. From the identification by the X-ray diffraction method and EPMA, it was assumed that the two Cu 3 Au type compounds obtained from the reactions of UN, Ru and Pd are the solid solution of URu 3 , dissolving a small amount of UPd 3 , and the solid solution of UPd 3 , dissolving a small amount of URu 3 , respectively. A UPd 3 solid solution with Table 1 The crystal structure and the lattice parameter of UMe 3 (Me: Ru, Rh, Pd) type intermetallic compounds Intermetallic compounds
Crystal structure
˚ Lattice parameters (A)
URu 3 URh 3 UPd 3
Cu 3 Au type Cu 3 Au type TiNi 3 type
a 0 53.98 [3] a 0 53.99 [4] a 0 55.757 c 0 59.621 [3]
UPd 4 (U: 18|20%)
Cu 3 Au type
a 0 54.06|4.07 [5]
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223
3 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out in more detail. The existence of the solid solution was discussed from the viewpoint of the variation of the lattice parameter of U–Pd intermetallic compounds and the transformation of the crystal structure from TiNi 3 type to Cu 3 Au type.
2. Experimental
Fig. 1. The results of the reactions of UN13 (Ru, Rh, Pd) at 1673 K under vacuum.
a small amount of URu 3 in a Cu 3 Au type structure was not reported until now. In this study, to understand the solubility of URu 3 in the Cu 3 Au type solid solution of UPd 3 , the reactions of UN1
UN was prepared from uranium metal by a hydride– dehydride–nitride process which referred to the work of Evans et al. [7]. The method for preparation of UN is as follows: 1. Hydriding uranium metal at 500 K, 2. decomposing the hydride and nitriding at 500|1673 K in purified nitrogen, 3. decomposing the nitride at 1673 K under vacuum.
Fig. 2. X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (x50.25, 0.50, 0.75) at 1673 K under vacuum.
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224
All the reactions were carried out sequentially in an impervious alumina tube. In the X-ray diffraction pattern of UN, a trace of UO 2 was observed. Ru and Pd powder with a purity of more than 99.9% was obtained from Nakarai Tesque Co. Ltd. The starting materials containing UN, Ru and Pd with the desired molar ratio were pressed into pellets at 600 kg cm 22 and heated in an electric furnace at 1673 K under vacuum (|10 22 Pa). The reaction products were identified by X-ray diffraction. The X-ray diffraction was performed at room temperature with Cu-Ka radiation on a Rigaku Rad r-A diffractometer equipped with a curved graphite monochromator. The distribution of elements in the reaction products was investigated by EPMA using Topkon MINI-SEM 100 and Horiba EMAX-8000 units.
3. Results and discussion From the previous work [6], the X-ray diffraction patterns for the reaction products between UN, Ru and Pd [UN13 (Ru x 1Pd 12x ), (x50.25, 0.50, 0.75)] at 1673 K under vacuum are redrawn in Fig. 2. Two Cu 3 Au type compounds are observed. From SEM and EPMA for these reaction products, it was assumed that the two Cu 3 Au type compounds are the intermetallic compounds between U and Ru, and between U and Pd, respectively. The starting compositions, the observed phases, and the lattice parameters of these two intermetallic compounds are compiled in Table 2. The relationship between the lattice parameter and the compositions of these compounds is illustrated in Fig. 3. As shown in Fig. 3, it is seen that the lattice parameters of both the first and the second phases are almost invariable. The first phase which has the smaller lattice constant may be URu 3 , because the lattice parameter of this phase is nearly equal to that of pure URu 3 , irrespective of the starting compositions. The molar ratio of U and Pd of the second phase, which has the higher lattice constant, is assumed to be about 1:3. Therefore, it can be considered that the solid solution of URu 3 (Cu 3 Au type) dissolving a small amount of UPd 3 , and the solid solution of UPd 3
Fig. 3. The relationship between the lattice parameter and the compositions of the reaction products of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum.
(Cu 3 Au type) dissolving a small amount of URu 3 , were obtained in the reactions between UN, Ru and Pd at 1673 K under vacuum. The UPd 3 solid solution which crystallizes in a Cu 3 Au type structure, with dissolving a small amount of URu 3 (Cu 3 Au type UPd 3 solid solution), was not reported until now. In order to identify the URu 3 content in the Cu 3 Au type UPd 3 solid solution, the reactions of UN13 (Ru x 1Pd 12x ), (x,0.25) at 1673 K under vacuum were carried out in the present study. The X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (0.11] # x] # 0.15) at 1673 K under vacuum are shown in Fig. 4. From this figure, only the Cu 3 Au type solid solution was observed at 0.12] # x] # 0.14. Thus, it was found that the solid solution of URu 3 and UPd 3 can be crystallized in a Cu 3 Au type structure when URu 3 content is in the region of 12|14%. The lattice parameter of the Cu 3 Au type UPd 3 solid
Table 2 The observed phases and the lattice parameter for the reaction products of UN and (Rd, Pd) at 1673 K under vacuum (UN:Me51:3)
Observed phases of
˚ Lattice parameters (A)
Ru
:
Pd
the reaction products
(the first phase)
(the second phase)
1 1 3
: : :
3 1 1
Cu 3 Au type (two phases)
a 0 53.98 — a 0 53.98
a 0 54.09 a 0 54.09 a 0 54.08
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225
Fig. 4. X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (0.11 # x # 0.15) at 1673 K under vacuum. ] ]
˚ is much higher than URu 3 (3.98 A ˚ solution (about 4.1 A) ˚ [4]) and UPd 4 (4.06 A ˚ [5]). The [3]), URh 3 (3.99 A relationship between the lattice parameter and the compositions of UPd 4 (U: 18|20 at %) in the previous study [5] are redrawn in Fig. 5. From this figure, it can be seen
that the value of the lattice parameter of the Cu 3 Au type UPd 3 solid solution corresponds to the extrapolated value of the lattice parameter of UPd 4 to 25%–U (U:Pd51:3). Usually, if Pd is removed from UPd 4 , Cu 3 Au type UPd 4 will be transformed to TiNi 3 type UPd 3 at about 22%–U
226
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Fig. 5. The extrapolation result of the lattice parameter of UPd 4 (U: 18|20%) to UPd 3 (U: 25%).
Fig. 7. The representation of Cu 3 Au type structure.
according to the phase diagram of the U–Pd system [2] (Fig. 6). In this study, however, the Cu 3 Au type solid solution of UPd 3 with a small amount of URu 3 was obtained. Thus it is assumed that if Ru is dissolved in UPd 4 from the beginning, the Cu 3 Au type structure will be maintained in the composition range of almost UPd 3 when Pd is removed from UPd 4 . Fig. 7 shows the Cu 3 Au type structure. Ordered Cu 3 Au type structure has a face centered cubic lattice, Me atoms occupy the face centered positions, and U atoms occupy the cornered positions. UPd 4 has this structure, in this case it is considered that Pd is placed on the U site partially at random. TiNi 3 type structure is shown in Fig. 8. The unit cell of TiNi 3 type hexagonal structure consists of three kinds of layers, A, B and C, and they stack in the period of
Fig. 6. The partial phase diagram for the Uranium–Palladium system [2].
ABACABAC–. The B layer is obtained by shifting the A layer to 2 / 3 in [100] direction and to 1 / 3 in [010] direction. The C layer is obtained by shifting the A layer to 1 / 3 in [100] direction and to 2 / 3 in [010] direction. The transformation from TiNi 3 type structure to Cu 3 Au type structure can be considered as follows. At first, the stacking period is turned into ABCABC– from ABACABAC– by shifting some planes in parallel as shown in Fig. 9(a). In this figure, a sub unit cell is indicated by the bold lines. From this figure, it is found that the length of the twelve edges constituting this cell are identical. In this cell, uranium atoms are placed on corners and palladium atoms are placed on face centers. However, this cell is not a Cu 3 Au type structure, since eight planes
Fig. 8. The representation of TiNi 3 type structure.
K. Kurosaki, M. Uno / Journal of Alloys and Compounds 274 (1998) 222 – 228
227
Fig. 9. The transformation from TiNi 3 type structure to Cu 3 Au type structure.
constituting this cell are not a square but a rhombus. The degree of interior angles of these rhomboid planes are 89.118 and 90.898, respectively. This unit cell and one of the rhomboid planes constituting this cell are shown in Fig.
9(b). Two diagonal lines of this plane are termed and , respectively. The length of the diagonal line corresponds to a 0 which is the lattice parameter of TiNi 3 type UPd 3 in Fig. 9(a), and the length of the diagonal line is calculated
228
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]]] as œ]31 a 20 1 ]41 c 20 . If these rhombus planes are changed to square, the rhombohedral structure is changed into the Cu 3 Au type cubic structure. In this case, the length of the two diagonal lines of the rhombus plane must be identical, ]]] c0 ] 2 2 in short a 0 5œ]13 a 0 1 ]14 c 0 → ] 5œ]83 . a0 To keep the atom movement as slight as possible during the above transformation, the diagonal line may become larger and / or the diagonal line may become shorter, i.e. in the original TiNi 3 type structure, a 0 must be lengthened and / or c 0 must be shortened. The lattice parameters of TiNi 3 type UPd 3 , a 0 and c 0 , ˚ and 9.621 A ˚ [3], respectively. If the value of are 5.757 A ˚ and the a 0 is fixed, c 0 must be decreased to 9.40 A, smallest Cu 3 Au type unit cell will be obtained. If the value ˚ and the of c 0 is fixed, a 0 must be increased to 5.89 A, largest Cu 3 Au type unit cell will be obtained. When the above transformation occurs, the lattice parameter of the thus obtained Cu 3 Au type unit cell is in the region of ˚ The lattice parameter of the Cu 3 Au type 4.07|4.17 A. ˚ UPd 3 solid solution obtained in this study (about 4.1 A) exists in this region. Thus, it is supposed that the transformation from TiNi 3 type to Cu 3 Au type is possible without relatively large atom movement. In the present study, UPd 3 solid solution with a Cu 3 Au type structure was obtained when it contained 12|14%– URu 3 . In order to clarify the reason why the dissolving of URu 3 causes the transformation of UPd 3 from TiNi 3 type structure to Cu 3 Au type structure, continued study is necessary.
4. Conclusion The reactions of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out. The products were identified by X-ray diffraction and EPMA. Two Cu 3 Au type compounds were obtained, one was the solid solution of URu 3 , dissolving a small amount of UPd 3 , and the other was the solid solution of UPd 3 , dissolving a small amount of URu 3 . Although the structure of pure UPd 3 is hexagonal TiNi 3 type, it was found that a new solid solution of UPd 3 , crystallizing in the Cu 3 Au type structure, could be obtained by doping with 12–14% URu 3 .
References [1] J.A. Catterall, J.D. Grogan, R.J. Pleasance, J. Inst. Metals 85 (1956–57) 63. [2] H. Kleykamp, S.G. Kang, Z. Metallkde. 82 (1991) 544. [3] T.J. Heal, G.I. Williams, Acta Crystallogr. 8 (1955) 494. [4] A.E. Dwight, J.W. Downey, R.A. Conner Jr., Acta Crystallogr. 14 (1961) 75. [5] M. Uno, K. Kurosaki, J. Nucl. Mater. 247 (1997) 322. [6] K. Kurosaki, M. Uno, to be published in the Journal of Alloys and Compounds 271–273 (1998) 641–644. [7] P.E. Evans, T.J. Davies, J. Nucl. Mater. 10 (1963) 43.
Journal of Alloys and Compounds 274 (1998) 222–228
Formation of the Cu 3 Au type solid solution of UPd 3 by doping a small amount of URu 3 Ken Kurosaki*, Masayoshi Uno Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, Yamadaoka 2 -1, Suita, Osaka 565 -0781, Japan Received 24 November 1997; received in revised form 21 March 1998
Abstract In order to investigate the formation of the Cu 3 Au type UPd 3 solid solution, reactions of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out. Two Cu 3 Au type compounds were obtained, one was a solid solution of URu 3 with a small amount of UPd 3 , and the other was a solid solution of UPd 3 with a small amount of URu 3 . Although pure UPd 3 has a hexagonal TiNi 3 type structure, a solid solution of UPd 3 with a Cu 3 Au type structure can be obtained when it contains URu 3 in the region of 12–14%. 1998 Elsevier Science S.A. Keywords: Uranium; Platinum-family metals; Solid solution; UPd 3 ; Cu 3 Au type structure
1. Introduction Platinum-family metal fission products (FP) have large fission yield in a nuclear reactor. In oxide fuel, platinumfamily metal FPs (Me: Ru, Rh, Pd) form mainly intermetallic compounds with other transition metal FPs and do not react with UO 2 , but in nitride fuel, platinum-family metals react with UN and form intermetallic compounds of the type UMe 3 . We have investigated the reaction behaviors between UN and Me because FPs may provide a large influence on the physical and chemical properties of the fuel. Although several studies on the binary phase diagrams for U–Me systems have been made [1,2], the ternary and quaternary phase diagrams are not reported. The crystal structures and the lattice parameters of UMe 3 type intermetallic compounds are summarized in Table 1. In the previous work for the pseudo-binary system [5], it was found that the reactions between UN and Ru, and between UN and Rh produced URu 3 and URh 3 as intermetallic compounds, respectively. In the reactions between UN and Pd, UPd 4 (U: 18|20%) was formed in addition to UPd 3 . *Corresponding author. Tel.: 181 6 8797906; fax: 181 6 8797889; e-mail: [email protected] 0925-8388 / 98 / $19.00 1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 98 )00544-1
The reactions of UN13 (Ru x 1Rh y 1Pd 12x 2y ), [0] # (x,y)] # 1] at 1673 K under vacuum (|10 22 Pa) for the pseudo-ternary and quaternary systems were carried out [6]. These results are redrawn in Fig. 1. The reactions between UN, Ru and Rh, and between UN, Rh and Pd produced a Cu 3 Au type solid solution. However, two compounds were obtained in the reactions between UN, Ru and Pd at any Pd ratio in the pseudo-ternary system, and between UN, Ru, Rh and Pd at the molar ratio of Ru:Rh:Pd51:1:4 in the pseudo-quaternary system. From the identification by the X-ray diffraction method and EPMA, it was assumed that the two Cu 3 Au type compounds obtained from the reactions of UN, Ru and Pd are the solid solution of URu 3 , dissolving a small amount of UPd 3 , and the solid solution of UPd 3 , dissolving a small amount of URu 3 , respectively. A UPd 3 solid solution with Table 1 The crystal structure and the lattice parameter of UMe 3 (Me: Ru, Rh, Pd) type intermetallic compounds Intermetallic compounds
Crystal structure
˚ Lattice parameters (A)
URu 3 URh 3 UPd 3
Cu 3 Au type Cu 3 Au type TiNi 3 type
a 0 53.98 [3] a 0 53.99 [4] a 0 55.757 c 0 59.621 [3]
UPd 4 (U: 18|20%)
Cu 3 Au type
a 0 54.06|4.07 [5]
K. Kurosaki, M. Uno / Journal of Alloys and Compounds 274 (1998) 222 – 228
223
3 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out in more detail. The existence of the solid solution was discussed from the viewpoint of the variation of the lattice parameter of U–Pd intermetallic compounds and the transformation of the crystal structure from TiNi 3 type to Cu 3 Au type.
2. Experimental
Fig. 1. The results of the reactions of UN13 (Ru, Rh, Pd) at 1673 K under vacuum.
a small amount of URu 3 in a Cu 3 Au type structure was not reported until now. In this study, to understand the solubility of URu 3 in the Cu 3 Au type solid solution of UPd 3 , the reactions of UN1
UN was prepared from uranium metal by a hydride– dehydride–nitride process which referred to the work of Evans et al. [7]. The method for preparation of UN is as follows: 1. Hydriding uranium metal at 500 K, 2. decomposing the hydride and nitriding at 500|1673 K in purified nitrogen, 3. decomposing the nitride at 1673 K under vacuum.
Fig. 2. X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (x50.25, 0.50, 0.75) at 1673 K under vacuum.
K. Kurosaki, M. Uno / Journal of Alloys and Compounds 274 (1998) 222 – 228
224
All the reactions were carried out sequentially in an impervious alumina tube. In the X-ray diffraction pattern of UN, a trace of UO 2 was observed. Ru and Pd powder with a purity of more than 99.9% was obtained from Nakarai Tesque Co. Ltd. The starting materials containing UN, Ru and Pd with the desired molar ratio were pressed into pellets at 600 kg cm 22 and heated in an electric furnace at 1673 K under vacuum (|10 22 Pa). The reaction products were identified by X-ray diffraction. The X-ray diffraction was performed at room temperature with Cu-Ka radiation on a Rigaku Rad r-A diffractometer equipped with a curved graphite monochromator. The distribution of elements in the reaction products was investigated by EPMA using Topkon MINI-SEM 100 and Horiba EMAX-8000 units.
3. Results and discussion From the previous work [6], the X-ray diffraction patterns for the reaction products between UN, Ru and Pd [UN13 (Ru x 1Pd 12x ), (x50.25, 0.50, 0.75)] at 1673 K under vacuum are redrawn in Fig. 2. Two Cu 3 Au type compounds are observed. From SEM and EPMA for these reaction products, it was assumed that the two Cu 3 Au type compounds are the intermetallic compounds between U and Ru, and between U and Pd, respectively. The starting compositions, the observed phases, and the lattice parameters of these two intermetallic compounds are compiled in Table 2. The relationship between the lattice parameter and the compositions of these compounds is illustrated in Fig. 3. As shown in Fig. 3, it is seen that the lattice parameters of both the first and the second phases are almost invariable. The first phase which has the smaller lattice constant may be URu 3 , because the lattice parameter of this phase is nearly equal to that of pure URu 3 , irrespective of the starting compositions. The molar ratio of U and Pd of the second phase, which has the higher lattice constant, is assumed to be about 1:3. Therefore, it can be considered that the solid solution of URu 3 (Cu 3 Au type) dissolving a small amount of UPd 3 , and the solid solution of UPd 3
Fig. 3. The relationship between the lattice parameter and the compositions of the reaction products of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum.
(Cu 3 Au type) dissolving a small amount of URu 3 , were obtained in the reactions between UN, Ru and Pd at 1673 K under vacuum. The UPd 3 solid solution which crystallizes in a Cu 3 Au type structure, with dissolving a small amount of URu 3 (Cu 3 Au type UPd 3 solid solution), was not reported until now. In order to identify the URu 3 content in the Cu 3 Au type UPd 3 solid solution, the reactions of UN13 (Ru x 1Pd 12x ), (x,0.25) at 1673 K under vacuum were carried out in the present study. The X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (0.11] # x] # 0.15) at 1673 K under vacuum are shown in Fig. 4. From this figure, only the Cu 3 Au type solid solution was observed at 0.12] # x] # 0.14. Thus, it was found that the solid solution of URu 3 and UPd 3 can be crystallized in a Cu 3 Au type structure when URu 3 content is in the region of 12|14%. The lattice parameter of the Cu 3 Au type UPd 3 solid
Table 2 The observed phases and the lattice parameter for the reaction products of UN and (Rd, Pd) at 1673 K under vacuum (UN:Me51:3)
Observed phases of
˚ Lattice parameters (A)
Ru
:
Pd
the reaction products
(the first phase)
(the second phase)
1 1 3
: : :
3 1 1
Cu 3 Au type (two phases)
a 0 53.98 — a 0 53.98
a 0 54.09 a 0 54.09 a 0 54.08
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225
Fig. 4. X-ray diffraction patterns for the reaction products of UN13 (Ru x 1Pd 12x ), (0.11 # x # 0.15) at 1673 K under vacuum. ] ]
˚ is much higher than URu 3 (3.98 A ˚ solution (about 4.1 A) ˚ [4]) and UPd 4 (4.06 A ˚ [5]). The [3]), URh 3 (3.99 A relationship between the lattice parameter and the compositions of UPd 4 (U: 18|20 at %) in the previous study [5] are redrawn in Fig. 5. From this figure, it can be seen
that the value of the lattice parameter of the Cu 3 Au type UPd 3 solid solution corresponds to the extrapolated value of the lattice parameter of UPd 4 to 25%–U (U:Pd51:3). Usually, if Pd is removed from UPd 4 , Cu 3 Au type UPd 4 will be transformed to TiNi 3 type UPd 3 at about 22%–U
226
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Fig. 5. The extrapolation result of the lattice parameter of UPd 4 (U: 18|20%) to UPd 3 (U: 25%).
Fig. 7. The representation of Cu 3 Au type structure.
according to the phase diagram of the U–Pd system [2] (Fig. 6). In this study, however, the Cu 3 Au type solid solution of UPd 3 with a small amount of URu 3 was obtained. Thus it is assumed that if Ru is dissolved in UPd 4 from the beginning, the Cu 3 Au type structure will be maintained in the composition range of almost UPd 3 when Pd is removed from UPd 4 . Fig. 7 shows the Cu 3 Au type structure. Ordered Cu 3 Au type structure has a face centered cubic lattice, Me atoms occupy the face centered positions, and U atoms occupy the cornered positions. UPd 4 has this structure, in this case it is considered that Pd is placed on the U site partially at random. TiNi 3 type structure is shown in Fig. 8. The unit cell of TiNi 3 type hexagonal structure consists of three kinds of layers, A, B and C, and they stack in the period of
Fig. 6. The partial phase diagram for the Uranium–Palladium system [2].
ABACABAC–. The B layer is obtained by shifting the A layer to 2 / 3 in [100] direction and to 1 / 3 in [010] direction. The C layer is obtained by shifting the A layer to 1 / 3 in [100] direction and to 2 / 3 in [010] direction. The transformation from TiNi 3 type structure to Cu 3 Au type structure can be considered as follows. At first, the stacking period is turned into ABCABC– from ABACABAC– by shifting some planes in parallel as shown in Fig. 9(a). In this figure, a sub unit cell is indicated by the bold lines. From this figure, it is found that the length of the twelve edges constituting this cell are identical. In this cell, uranium atoms are placed on corners and palladium atoms are placed on face centers. However, this cell is not a Cu 3 Au type structure, since eight planes
Fig. 8. The representation of TiNi 3 type structure.
K. Kurosaki, M. Uno / Journal of Alloys and Compounds 274 (1998) 222 – 228
227
Fig. 9. The transformation from TiNi 3 type structure to Cu 3 Au type structure.
constituting this cell are not a square but a rhombus. The degree of interior angles of these rhomboid planes are 89.118 and 90.898, respectively. This unit cell and one of the rhomboid planes constituting this cell are shown in Fig.
9(b). Two diagonal lines of this plane are termed and , respectively. The length of the diagonal line corresponds to a 0 which is the lattice parameter of TiNi 3 type UPd 3 in Fig. 9(a), and the length of the diagonal line is calculated
228
K. Kurosaki, M. Uno / Journal of Alloys and Compounds 274 (1998) 222 – 228
]]] as œ]31 a 20 1 ]41 c 20 . If these rhombus planes are changed to square, the rhombohedral structure is changed into the Cu 3 Au type cubic structure. In this case, the length of the two diagonal lines of the rhombus plane must be identical, ]]] c0 ] 2 2 in short a 0 5œ]13 a 0 1 ]14 c 0 → ] 5œ]83 . a0 To keep the atom movement as slight as possible during the above transformation, the diagonal line may become larger and / or the diagonal line may become shorter, i.e. in the original TiNi 3 type structure, a 0 must be lengthened and / or c 0 must be shortened. The lattice parameters of TiNi 3 type UPd 3 , a 0 and c 0 , ˚ and 9.621 A ˚ [3], respectively. If the value of are 5.757 A ˚ and the a 0 is fixed, c 0 must be decreased to 9.40 A, smallest Cu 3 Au type unit cell will be obtained. If the value ˚ and the of c 0 is fixed, a 0 must be increased to 5.89 A, largest Cu 3 Au type unit cell will be obtained. When the above transformation occurs, the lattice parameter of the thus obtained Cu 3 Au type unit cell is in the region of ˚ The lattice parameter of the Cu 3 Au type 4.07|4.17 A. ˚ UPd 3 solid solution obtained in this study (about 4.1 A) exists in this region. Thus, it is supposed that the transformation from TiNi 3 type to Cu 3 Au type is possible without relatively large atom movement. In the present study, UPd 3 solid solution with a Cu 3 Au type structure was obtained when it contained 12|14%– URu 3 . In order to clarify the reason why the dissolving of URu 3 causes the transformation of UPd 3 from TiNi 3 type structure to Cu 3 Au type structure, continued study is necessary.
4. Conclusion The reactions of UN13 (Ru x 1Pd 12x ) at 1673 K under vacuum were carried out. The products were identified by X-ray diffraction and EPMA. Two Cu 3 Au type compounds were obtained, one was the solid solution of URu 3 , dissolving a small amount of UPd 3 , and the other was the solid solution of UPd 3 , dissolving a small amount of URu 3 . Although the structure of pure UPd 3 is hexagonal TiNi 3 type, it was found that a new solid solution of UPd 3 , crystallizing in the Cu 3 Au type structure, could be obtained by doping with 12–14% URu 3 .
References [1] J.A. Catterall, J.D. Grogan, R.J. Pleasance, J. Inst. Metals 85 (1956–57) 63. [2] H. Kleykamp, S.G. Kang, Z. Metallkde. 82 (1991) 544. [3] T.J. Heal, G.I. Williams, Acta Crystallogr. 8 (1955) 494. [4] A.E. Dwight, J.W. Downey, R.A. Conner Jr., Acta Crystallogr. 14 (1961) 75. [5] M. Uno, K. Kurosaki, J. Nucl. Mater. 247 (1997) 322. [6] K. Kurosaki, M. Uno, to be published in the Journal of Alloys and Compounds 271–273 (1998) 641–644. [7] P.E. Evans, T.J. Davies, J. Nucl. Mater. 10 (1963) 43.