LANTHANUM-YTT R I U M
12.2,1, u ,
o ~ DHCP
1 2 . 0 - ~ o
26.8
o< 2 6 . 6 -
d z õ
cn 5.81 -o 59 V«l 66 Lun
• 66 Joy I- •
5 . 8 4 - 64 Hor J
5.8C -
5.-?6
5.72 0 Lo
o 1
30 K.A. GSCHNEIDNER mad F.W. CALDERWOOD
scatter. L u n d i n did not index the film of a sample containing 52 at% yttrium because of poor resolution of the lines; he observed that two phases were present. Jayaraman et al. (1966) did not give spacings for specimens having 60 and 70at% Y but observed that each had hcp structure.
2.10.3. Phase relationships as a function of pressure
J a y a r a m a n et al. (1966) studied pressure-induced transformations in the l a n t h a n u m - y t t r i u m system using a piston-cylinder apparatus. Appropriate amounts of the metals (no purities stated) were arc-melted under an argon atmosphere, then heat-treated at 500°C for several days in sealed evacuated quartz tubes. The annealed specimens were single-phase materials of the expected structure. After a 5 hr anneal at 4.0 GPa pressure and 450°C, temperature was reduced to ambient and pressure was released. The X-ray patterns were again recorded and magnetic-sus- ceptibility measurements down to 1.4 K were made by using a pendulum magne- tometer. A 30 at% La specimen, normally having a hcp structure, underwent no phase transition; a 40at% La specimen, also normally having hcp structure was transformed to Sm-type structure; a 50 at% La specimen, normally having Sm-type structure, transformed to the dhcp structure. The transformations are sluggish and conversion to the high pressure form is temperature- and time-dependent; therefore, n o attempt was made to identify the transition pressure.
References
Harris, I.R. and G.V. Raynor, 1964, J. Less-Common Met. 7, 1.
Jayaraman, A., R.C. Sherwood, H.J. Williams and E. Corenzwit, 1966, Phys. Rev. 148, 502,
Lundin, C.E., 1966, Final Report, Denver Research Institute Rept. AD-633558, University of Denver, CO (also given as DRI-2326).
Spedding, F.H,, R.M. Valletta and A.H. Daane, 1962, Trans. Quarterly (Am. Soc. Met.) 55, 483.
Valletta, R.M., 1959, Ph.D. thesis, Iowa State University, Ames, IA.
2.11. Ce-Pr: Cerium-praseodymium 2.11.1. Phase diagram
Altunbas and Harris (1980) studied the cerium-praseodymium alloy system using electrical resistivity, X-ray diffraction and differential thermal analysis (DTA) tech- niques. In most of the research they used " s t a n d a r d commercial" material but some
"relatively p u r e " praseodymium (purified by solid state electrolysis) was used in the D T A measurements. Appropriate amounts of the component metals were arc-melted in purified argon, turned and remelted several times. This was followed by a seven d a y vacuum anneal at 600°C with slow cooling to room temperature. Their electrical resistivity curves for the praseodymium sample indicated only one solid phase transformation (dhcp ~ bcc) whereas the curves for cerium and the C e - P r alloys exhibited two transitions, dhcp ~ fcc (below 61°C for pure cerium) and fcc ~- bcc.
The hysteresis that accompanied the dhcp-fcc transition increased as the cerium content increased. The resistivity data for praseodymium were in good agreement with those of Spedding et al. (1957) and their transition temperature for the y-/3 (fcc-dhcp) phase change in cerium was similar to values reported by Gschneidner et al. (1962a) and by McHargue and Yakel (1960). The spread in these reported values is probably due to different impurity levels in the alloys investigated. An X-ray diffraction study (Altunbas and Harris) on powders that had been annealed at 600°C for 2 hr and quickly cooled to room temperature showed that: (1) alloys in the range 0 to 65 at% Pr have fcc structure; (2) alloys in the range 74 to 100 at% Pr have dhcp structure; and (3) alloys containing 66 to 74 at% Pr contained both the dhcp and fcc phases. Altunbas and Harris correlated the predominance of the fcc structure with the hysteresis characteristics of these alloys. They found considerable hysteresis associated with the fcc-dhcp transformation in Ce-rich alloys, which they associated with a change in the transformation mechanism from a martensitic to diffusion-controlled process. They observed a rapid nonlinear increase for the linear increase for the temperature dependence of the solvus lines that separate the fcc from the dhcp-phase regions. They postulated that either the dhcp + fcc-phase field meets the bcc + fcc-phase field just before 100% Pr to give a high temperature eutectoid or peritectoid reaction, or that the dhcp-fcc transition occurs in commer- cial praseodymium just below a bcc-fcc transition. If the latter were true, the resistivity and DTA effects associated with the dhcp-fcc phase change merged with the effects due to the bcc ~ fcc transformation. Altunbas and Harris believed that if
1200
I000
8O0 d
~- 6 0 0
n ~ w 13..
ù' 4 0 0
F--
2 0 0 m
j /
0 61" I I i I
0 20 40 60 80
CE R I U M - PRASEODYMIU M
I ! I
LIQUID
9 3 1 E
798 °
~
18 Ce,/3 P r ) - 7 5 0 - ~ ~ ~-';r26 . . . . . . . .1
( x C e ) FCC / / / /
/ /
« /
_ / /
/ 7 D H C P
7 7 ( ~ Ce,e P r )
Ce ATOMI C PERCENT PRASEODYMIUM I00
Pr
Fig. 19. Phase diagram of the cerium-praseodymium system. The 61°C value for the 7-/Y (fcc-dhcp) transformation for pure cerium is the midpoint value of the heating (139°C) and cooling ( - 1 6 ° C ) transformation temperatures (see table 1).
32 K.A. GSCHNEIDNER and F.W. CALDERWOOD
the C e - P r alloys could be prepared f r o m pure c o m p o n e n t s the f c c - d h c p - p h a s e field would shift to lower Pr contents and a phase d i a g r a m similar to that of the L a - N d system (see section 2.3 and fig. 3) would be anticipated. Their D T A and solidifica- tion data indicated a narrow liquidus-solidus separation, as expected in an intra rare earth alloy system of this kind.
G s c h n e i d n e r et al. (1961 and 1962b) investigated the effect of alloying on the 7 ~ et transition temperature of cerium and found that the addition of 2at% Pr lowers this transition temperature. At high pressures, this addition of Pr raised the t r a n s f o r m a t i o n pressure of pure cerium.
Figure 19 is the reviewers' interpretation of the phase relationships in the c e r i u m - p r a s e o d y m i u m system based on the experimental data presented by A l t u n b a s a n d Harris. Melting and transition temperatures of the pure c o m p o n e n t metals have been adjusted to conform with table 1.
2.11.2. Lattice spacings
Published lattice spacing data for the c e r i u m - p r a s e o d y m i u m system are limited to the pure c o m p o n e n t s and to several cerium-rich alloys. Gschneidner et al. (1962c) examined lattice spacings for several cerium-rich alloys containing up to 5 at% of several rare earth metals. The experimental details are given in section 2.2.2. T h e y f o u n d that the lattice spacings for all of these alloys except those with p r a s e o d y m i u m showed a positive deviation from Vegard's linear approximation whereas the lattice spacings for the c e r i u m - p r a s e o d y m i u m alloys, shown in fig. 20, followed Vegard's law quite weil.
References
Altunbas, M. and I,R. Harris, 1980, J. Mater. Sci. 15, 693.
Gschneidner, K.A., Jr., R.R. McDonald and R.O. Elliott, 1961, Phys. Rev. Lett. 6, 218.
Gschneidner, K.A., Jr., R.O. Elliott and R.R. McDonald, 1962a, J. Phys. Chem. Solids 23, 555.
Gschneidner, K.A., Jr., R.O. Elliott and R.R. McDonald, 1962b, J. Phys. Chem. Solids 23, 1201.
Gschneidner, K.A., Jr., R.O. Elfiott and M.Y. Prince, 1962c, in: Nachman, J.F. and C.E, Lundin, eds., Rare Earth Research (Gordon and Breach, New York) p. 71.
McHargue, C.J. and H.L. Yakel, 1960, Acta Metall. 8, 637.
Spedding, F.H., A.H. Daane and K.W. Hermann, 1957, J. Met. 9, 895.
CER IU M - PRASEODYMIUM o ~
5 . 1 7 , , , ,
z
5.16,0
t~ 5 . 1 6 ~- ,, '~ o o IM _o
I - I--
< 5.15 ._1 0
Ce
1
FCC phase I
I I I I Fig. 20. Lattice spacings in the I 2 3 4 5 cerium-rich end of the cerium- ATOM IC PERCENT PRASEODYM IUM praseodymium system.
CERIUM-NEODYMIUM
+,o 68 Spe
• 62 Gsc
5.17]
/ ~ . 1 6 1 0 5 . 1 6 / ~ ' ~ +
o ~
d I FCC
»
z 3 . 6 8
O_
I.iJ
:3.67
I-- ).-
/
3.66
{3
i I i
0
~~cP
11.-/966 DHCP
3,6582
3.65 I ! | I
0 2 0 40 60 80 I00
Ce ATOMIC PERCENTNEODYMIUM Nd
11.84
11.85 o~
(.9 Z
11.82 o_ (/)
b_l I 1
1.81 ~-
11.80
Fig. 21. Lattice spacings in the cerium-neodymium system. The straight lines show Vegard's law rela- tionshJps based on data from table 2.
2.12. Ce-Nd: Cerium-neodymium 2.12.1. Lattice spacings
N o phase diagram for the cerium-neodymium system was found in the literature, b u t Speight et al. (1968) have measured the room temperature lattice spacings for this alloy system. Their alloy specimens were made from the cerium metal that contained no more than 100ppm of other rare earth metals and from neodymium metal that contained approximately 200ppm of non-rare earth metals and
< 1000 p p m of other rare earth metals. Lattiee spacings were determined by X-ray diffraction and a N e l s o n - R i l e y extrapolation was used to eliminate systematic errors. Their data for the cerium-neodymium system, reported in kX units, have been converted to angstrom units and are plotted in fig. 21. In the cerium-rich fcc region, the lattice spacings appear to be independent of composition. A small deviation from ideality exists for both the a and the c lattice spacings in the dhcp region exeept at N d content greater than 90 at% where a small negative deviation from ideality exists.
In addition to this work (Speight et al.), Gschneidner et al. (1962) reported the lattice parameter of a cerium-rich alloy containing 2at% Nd. The experimental details are given in section 2.2.2.
34 K.A. GSCHNEIDNER and F.W. CALDERWOOD
References
Gschneidner, K.A., Jr., R.O. Elliott and M.Y. Prince, 1962, in: Nachman J.R. and C.E. Lundin, eds., Rare Earth Research (Gordon and Breach, New York) p. 71.
Speight, J.D., I.R. Harris and G.V. Raynor, 1968, J. Less-Common Met. 15, 317.
2.13. Ce-Sm: Cerium-samarium 2.13.1. Phase diagram
A partial phase diagram for the cerium-samarium alloy system has been reported by Terekhova et al. (1968) and by Torchinova et al. (1971). A comparison of the two published phase diagrams indicates that each is based on the same research. The purity of the cerium and samarium metals was not reported. The phase relationships were determined by metallographic, X-ray diffraction, thermal analysis, hardness, thermad expansion and magnetic-susceptibility measurements. Neither Terekhova et al. nor Torchinova et ad. considered the existence of the high temperature hcp form of samarium (flSm) in the construction of their phase diagram. Consequently, the reviewers have made revisions in their phase diagram to include the flSm phase. The revised diagram is shown in fig. 22. Here, the liquidus-solidus is shown as a single straight line connecting the melting points of the pure components since their atomic numbers differ by only four (see discussion in section 2.1.1). The solid solution ranges at room temperature shown in fig. 22 are based on the lattice parameter data (see section 2.13.2) reported by Speight et al. (1968). The temperature shown for the
1200
I 0 0 0
o 8 0 0
0
d
~- 600
<~
w ù' 4 0 0
C E R I U M - S A M A R I U M
I I I t i
L I Q U I D ic)
. / ~ 9 2 2 " 1
7 9 8 o .-.-.- ~ ~ ~ I , . - - /
I " ( 8 Ce ) ' S m ) .--.- ...--- ..--- ~ --" Pl~~ "-4
?26- . . - ' - - - " S ~ ~ ~ (~sù~~ ,=,-_1
~ -- Ii//11
/ oùcP / // -1
// ~ùc,, // / /
/ /
2 0 0 / / 0 v 6 1 =
0
20 I 4 0 I/ l¢z Sm ) -
/ / R H O M B
/ /
_/ /
/
/ [ eO'/o
6 0 I 8 0 I00 Ce A T O M I C PERCENT SAMARIUM Sm
Fig. 22. Phase diagram of the cer- ium-samarium system.
transformation of 7 Ce to/3 Ce (61°C) is the average temperature of this transfor- mation on heating and on cooling. Much of the phase diagram between the liquidus and the room temperature region is uncertain but the diagram presented here is a logical interpretation of the reported data and the existence of a continuous series of solid solutions between dhcp and hcp rare earth metals, see section 2.1.4. The original diagram presented by Terekhova et al. and Torchinova et al. showed bcc solid solution reacting with the rhombohedral aSm phase to form the dhcp /3Ce solid solution by a peritectoid reaction. However, the thermal analysis data points given by these investigators are in good agreement with the solvus lines separating the bcc phase from the dhcp-hcp solid solution shown in fig. 22.
Clinard (1967) used electrical resistivity measurements to study the B-phase forming tendencies of cerium alloys between 300 and 1.5 K. The addition of 2 at%
samarium to cerium resulted in a hysteresis loop in the temperature vs. resistivity curve between approximately 40 and 170 K. This was attributed to the formation of some aCe during thermal cycling.
2.13.2. Lattice spaeings
Speight et al. (1968) reported lattice spacings at room temperature for cerium-samarium alloys that had been rapidly cooled from 600°C. Their samarium
z
0
3.66-
(/')
~ 3 , 6 5
«
..J o
3.64 -
3 . 6 3 -
CERIUM-SAMARIUM
5.171
, ,F C C
5.16 ~ +
~°J \
3.67
I I
3"620 20
Ce ATOMIC FERCENT SAMARIUM
O
O