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High pressure phases in the MnYb system
Journal of the Less-Common Metals, 90 (1983) 211-215
HIGH PRESSURE
PHASES
A. V. TSVYASHCHENKO
IN THE Mn-Yb
211
SYSTEM
and S. V. POPOVA
Znstitute ofHigh Pressure Physics of the U.S.S.R. Academy of Sciences, Moscow (U.S.S.R.) (Received June 28,1982)
Summary The crystallization of the intermetallic compounds in the Mn-Yb system was investigated at a pressure of 7.7 GPa and temperatures up to 1300 “C. The new phases Yb,Mn,,, Yb,Mn,, and Yb,Mn,, all of which are metastable at room pressure, were found under these conditions.
1. Introduction It is known that no intermediate phases exist in the Mn-Yb system at atmospheric pressure although Eatough and Hall [l] found that the hexagonal phase YbMn, can be prepared at high pressures and temperatures. It has an MgZn,-type structure (C14) and a unit cell with parameters a = 5.233 +0.003 A and c = 8.561 f 0.005 A. We investigated the possibility of the crystallization of other phases in this system at high pressure.
2. Experimental
procedure
The experiments were carried out at a constant pressure of 7.7 GPa in a chamber constructed by Khvostantsev et al. [Z]. The samples were prepared from a mixture of powdered ytterbium (purity, 99.8%) and manganese (nurity, 99.99%). The powdered metals were mixed well, pressed and then placed in a pipestone ampoule. A tantalum heater was used in which the temperature was controlled by a chromel-alumel thermocouple located externally near the heater wall. The experiments were carried out at different temperatures up to 1350 “C for periods of 2-15 min. The phases were detected on X-ray powder photographs obtained using Cu Ku radiation and a camera of diameter 114 mm. A mixture with NaCl or CaF, was used to determine the unit cell sizes of the new phases. The composition of 0022-5088/83/0000-OOOO/$O3.00
0 Elsevier Sequoia/Printed
in The Netherlands
212
the alloys was determined by X-ray microanalysis Yb.
with an accuracy
to f 1 at.%
3. Results The main results of the experiments are listed in Table 1. Three new phases Yb,Mn,, and Yb,Mn,) were detected at high pressure in addition to (Yb,Mn,,, the Laves phase YbMn, discussed above. The X-ray powder data for Yb,Mn,, (Table 2) were indexed on the basis of a cubic unit cell with lattice parameter a = 12.189 & 0.005 A (21 at.% Yb) and space group Fm3m; therefore the Th,Mn 23 type of structure was assumed. This structure has four molecules in the unit cell and the calculated density is 8.44 g cmP3. The density was measured pycnometrically and was found to be 8.4 + 0.1 g cmm3. On annealing in a vacuum at 700 “C this phase decomposes into the constituent elements. Yb,Mn, and Yb,Mn, (Table 3) were obtained in an impure form and so their densities were not measured. However, all the lines on the powder photographs could be assigned on the basis of hexagonal unit cells with the following parameters: a = 11.336f0.005 A and c = 4.029f0.004 A (59 at.% Yb) for Yb,Mn,; a = 8.49 + 0.01 A and c = 7.88 rfi0.01 A (12 at.% Yb) for Yb,Mn,,. ThereTABLE 1 The phases presented in the samples prepared at P = 7.7 GPa
Initial composition (at.% Yb)
Phase
Structure
Unit cell dimensions (A)
(&) a
60
900
60
1100
60
1250
33
1000
33
1100
33
1200
33 21 21
1300 1200 1350
20
1200
Yb YbMn, Yb YbMn, Yb YbMn,
F.c.c. MgZn, F.c.c. Mgk F.c.c. MgZn,
Yb,Mn,, Yb Mn YbMn, Mn Yb,Mn, YbMn,
Th,Mn,, F.c.c. a-Mn M&W a-Mn Ho&o, MgZn,
Yb,Mn,, Yb,Mn,, Yb,Mn,, Mn Yb,Mn, Yb,Mn,,
Th,Mn,, Th,Mn,, Th,Mn,, a-Mn Ho&o, Th,Mn,, Th,Ni,,
Yb,Mn,,
5.49&0.01 5.24 f 0.01 550~0.01 5.25 k 0.01 5.50 * 0.01 5.229 * 0.003 12.18kO.03 5.47 f 0.01 8.91 f 0.01 5.22 f 0.01 8.94 f 0.01 11.336f0.005 5.231 kO.003 12.21 kO.03 12.19*0.01 12.189~0.005 8.97 f 0.01 11.30 f 0.02 12.19f0.01 8.48kO.03
C
8.60f0.05 8X3+0.05 8.560 f 0.005
8.54 k 0.06 4.029 * 0.004 a.563 f 0.005
4.02 f 0.01 7.89kO.03
213
TABLE 2
X-raydatafor YbMn, andYb,Mn,, YbMnz” Intensity’
%Mnz
d(meas)
hkl
(A)
MS MS MS MS S S VW S MS W VW W W MS MS S MS MS W ‘a = ba = ‘VS, very
4.517 4.279 3.999 3.110 2.608 2.411 2.265 2.228 2.187 2.146 1.936 1.773 1.709 1.599 1.510 1.468 1.423 1.307 1.208
d(calc)
Zntensity’
(A) 100 002 101 102 110 103 200 112 201 004 104 203 210 105 300 123 302 220 206
4.522 4.281 4.004 3.109 2.611 2.414 2.261 2.229 2.186 2.141 1.935 1.772 1.709 1.601 1.507 1.466 1.422 1.305 1.207
b
d(meas)
hkl
(A)
MS W S MS S S W MS W W MS MS W VW VW W VW
3.518 3.041 2.793 2.490 2.346 2.154 2.032 1.706 1.588 1.528 1.490 1.435 1.408 1.332 1.245 1.224 1.178
h(calc) (A)
222 400 331 422 511 440 442 551 553 800 733 660 555 753 844 755 773
3.519 3.048 2.797 2.488 2.346 2.155 2.032 1.710 1.587 1.524 1.489 1.437 1.408 1.338 1.244 1.225 1.178
5.231k0.003A; c = 8.563f0.005A; c/a = 1.64. 12.189+0.005 A. very strong; S, strong; MS, medium strong; M, medium; MW, medium weak; W, weak; VW, weak.
fore we can tentatively assume that these phases have structures of the Ho,Co, and Th*Ni,, types respectively. The solid solution a-Mn(Yb) was also found in the samples prepared at high about 2 at.% Yb and had a unit cell dimension pressure; it contained a = 8.94 kO.01 A.
4. Conclusion Four intermediate phases can be obtained in the Mn-Yb system at high pressures and temperatures. Their compositions and crystal structures are similar to those obtained in other binary RE-T systems (RE = rare earth; T = Mn, Fe, Ni, Co). It is of interest to discuss the atomic volume and valence of ytterbium metal in these compounds. Wang and Holder [3] concluded that the absence of Yb,Mn,, from the Mn-Yb system under normal conditions suggests that ytterbium tends not to exist in the trivalent state in its alloys with manganese. However, it is well known that, apart from europium and ytterbium, the sizes of
214
TABLE 3 X-ray data for M,Mn,
and Yb,Mn,,
YbdMn3’ Intensity’
d(meas)
hkl
(A)
vs vs MS vs S
vs
2.821 2.724 2.142 1.963 1.636 1.613
MS MS W
1.567 1.463 1.417 1.255 1.157 1.150
MS M VW VW
1.074 1.066 1.017 0.997
VW
VW
vs
220 310 140 500 231 600 430 511 250 521 440 450 442 180 721 820 371 740 380
di(calc)
di(meas)
(A)
(A)
2.833 2.722 2.142 1.963 1.966 1.636 1.614 1.615 1.572 1.464 1.417 1.257 1.159 1.149 1.149 1.071 1.065 1.017 0.997
VW M S S VW MW VW VW VW VW VW VW MW
2.619 2.441 2.127 2.081 1.905 1.869 1.790 1.602 1.535 1.509 1.490 1.368 1.228
hkl
d(calc) (A)
121 300 220 302 123 222 114 124 304 403 142 125 600
2.621 2.451 2.122 2.081 1.909 1.869 1.787 1.607 1.536 1.506 1.486 1.371 1.225
‘a = 11.336+0.005ii; c = 4.029~0.004xi; c/a = 0.36. ba = 8.49kO.01A; c = 7.88~0.01 A; c/a = 0.93. ‘Abbreviations aa defined in Table 2.
RE metals decrease with increasing atomic mass and that this characteristic is apparently associated with the tendency of these metals to exhibit a divalent character. The average atomic volume AAV (defined as the volume of the unit cell divided by the number of atoms present in the cell) of the compounds RE,T, -x also decreases with increasing atomic mass of the RE component provided that T is unchanged. The dependence of the AAV on the atomic mass is shown in Fig. 1 for REMn, (Cl4 and C15) and RE,Mn,, (D8a). Examination of these data shows that the AAVs of YbMn, and Yb,Mn,, lie on the same lines as the other compounds. Therefore we can conclude that ytterbium behaves like other trivalent metals. We now consider the change in volume during the crystallization of the RE,T, _X compounds. This change is not large, and so the AAVs of these phases are located near the additive line connecting the atomic volumes of the pure elements. This does not apply to europium and ytterbium because, as was mentioned above, they are anomalously large. If we assume that ytterbium is trivalent, its atomic volume must be about 29.8 A3 atom-’ instead of the usual 41.28 A3 atom- i. The data in Fig. 2 show that in this case the AAVs of the high pressure phases Yb,Mn,, YbMn,, Yb,Mn,, and YbzMnl, lie near the additive line. The AAVs of the intermediate phases of the systems Yb-Fe, Er-Mn and Er-Co
215
i5b
Yb
I
im
IcdlTb
164
168
iDj IHo IEtlTu
82
i7b
IYb Ilu
“’ M,o.u.
Fig. 1. The dependence of the AAV of REMn, and RE,Mn,, on the atomic mass of the RE element: A, structure type C15; 0, structure type C14; @, structure type D8a; 0, YbMn,; 0, Yb,Mn,,. Fig. 2. The dependence of the AAVs of the intermediate phases of binary RE-T systems (RE = Yb,Er; T s Mn,Fe,Co) on the T content. are included in Fig. 2 for comparison (the unit cell sizes of these phases were taken from refs. 4-6). Therefore we can conclude that high pressures induce a trivalent character in ytterbium.
Acknowledgments The authors are greatly indebted to Mrs. R. F. Aksenova Bushuev for their help with the experimental work.
and Mr. A. V.
References 1 2
3 4 5 6
N. L. Eatough and H. T. Hall, Inorg. Chem., 11(1972) 2608. L. G. Khvostantsev, L. F. Vereshchagin and A. P. Novikov, High Temp. High Pressures, 9 (1977) 637. F. E. Wang and J. P. Holder, Trans. Metall. Sot. AIME, 233(1965) 731. K. N. R. Taylor, A& Phys., 20 (1971) 551. J. F. Cannon, D. L. Robertson and H. T. Hall, Muter. Res. Bull., 7(1972) 5. K. H. J. Buschow, J. Less-Common Met., 26(1972) 329.
HIGH PRESSURE
PHASES
A. V. TSVYASHCHENKO
IN THE Mn-Yb
211
SYSTEM
and S. V. POPOVA
Znstitute ofHigh Pressure Physics of the U.S.S.R. Academy of Sciences, Moscow (U.S.S.R.) (Received June 28,1982)
Summary The crystallization of the intermetallic compounds in the Mn-Yb system was investigated at a pressure of 7.7 GPa and temperatures up to 1300 “C. The new phases Yb,Mn,,, Yb,Mn,, and Yb,Mn,, all of which are metastable at room pressure, were found under these conditions.
1. Introduction It is known that no intermediate phases exist in the Mn-Yb system at atmospheric pressure although Eatough and Hall [l] found that the hexagonal phase YbMn, can be prepared at high pressures and temperatures. It has an MgZn,-type structure (C14) and a unit cell with parameters a = 5.233 +0.003 A and c = 8.561 f 0.005 A. We investigated the possibility of the crystallization of other phases in this system at high pressure.
2. Experimental
procedure
The experiments were carried out at a constant pressure of 7.7 GPa in a chamber constructed by Khvostantsev et al. [Z]. The samples were prepared from a mixture of powdered ytterbium (purity, 99.8%) and manganese (nurity, 99.99%). The powdered metals were mixed well, pressed and then placed in a pipestone ampoule. A tantalum heater was used in which the temperature was controlled by a chromel-alumel thermocouple located externally near the heater wall. The experiments were carried out at different temperatures up to 1350 “C for periods of 2-15 min. The phases were detected on X-ray powder photographs obtained using Cu Ku radiation and a camera of diameter 114 mm. A mixture with NaCl or CaF, was used to determine the unit cell sizes of the new phases. The composition of 0022-5088/83/0000-OOOO/$O3.00
0 Elsevier Sequoia/Printed
in The Netherlands
212
the alloys was determined by X-ray microanalysis Yb.
with an accuracy
to f 1 at.%
3. Results The main results of the experiments are listed in Table 1. Three new phases Yb,Mn,, and Yb,Mn,) were detected at high pressure in addition to (Yb,Mn,,, the Laves phase YbMn, discussed above. The X-ray powder data for Yb,Mn,, (Table 2) were indexed on the basis of a cubic unit cell with lattice parameter a = 12.189 & 0.005 A (21 at.% Yb) and space group Fm3m; therefore the Th,Mn 23 type of structure was assumed. This structure has four molecules in the unit cell and the calculated density is 8.44 g cmP3. The density was measured pycnometrically and was found to be 8.4 + 0.1 g cmm3. On annealing in a vacuum at 700 “C this phase decomposes into the constituent elements. Yb,Mn, and Yb,Mn, (Table 3) were obtained in an impure form and so their densities were not measured. However, all the lines on the powder photographs could be assigned on the basis of hexagonal unit cells with the following parameters: a = 11.336f0.005 A and c = 4.029f0.004 A (59 at.% Yb) for Yb,Mn,; a = 8.49 + 0.01 A and c = 7.88 rfi0.01 A (12 at.% Yb) for Yb,Mn,,. ThereTABLE 1 The phases presented in the samples prepared at P = 7.7 GPa
Initial composition (at.% Yb)
Phase
Structure
Unit cell dimensions (A)
(&) a
60
900
60
1100
60
1250
33
1000
33
1100
33
1200
33 21 21
1300 1200 1350
20
1200
Yb YbMn, Yb YbMn, Yb YbMn,
F.c.c. MgZn, F.c.c. Mgk F.c.c. MgZn,
Yb,Mn,, Yb Mn YbMn, Mn Yb,Mn, YbMn,
Th,Mn,, F.c.c. a-Mn M&W a-Mn Ho&o, MgZn,
Yb,Mn,, Yb,Mn,, Yb,Mn,, Mn Yb,Mn, Yb,Mn,,
Th,Mn,, Th,Mn,, Th,Mn,, a-Mn Ho&o, Th,Mn,, Th,Ni,,
Yb,Mn,,
5.49&0.01 5.24 f 0.01 550~0.01 5.25 k 0.01 5.50 * 0.01 5.229 * 0.003 12.18kO.03 5.47 f 0.01 8.91 f 0.01 5.22 f 0.01 8.94 f 0.01 11.336f0.005 5.231 kO.003 12.21 kO.03 12.19*0.01 12.189~0.005 8.97 f 0.01 11.30 f 0.02 12.19f0.01 8.48kO.03
C
8.60f0.05 8X3+0.05 8.560 f 0.005
8.54 k 0.06 4.029 * 0.004 a.563 f 0.005
4.02 f 0.01 7.89kO.03
213
TABLE 2
X-raydatafor YbMn, andYb,Mn,, YbMnz” Intensity’
%Mnz
d(meas)
hkl
(A)
MS MS MS MS S S VW S MS W VW W W MS MS S MS MS W ‘a = ba = ‘VS, very
4.517 4.279 3.999 3.110 2.608 2.411 2.265 2.228 2.187 2.146 1.936 1.773 1.709 1.599 1.510 1.468 1.423 1.307 1.208
d(calc)
Zntensity’
(A) 100 002 101 102 110 103 200 112 201 004 104 203 210 105 300 123 302 220 206
4.522 4.281 4.004 3.109 2.611 2.414 2.261 2.229 2.186 2.141 1.935 1.772 1.709 1.601 1.507 1.466 1.422 1.305 1.207
b
d(meas)
hkl
(A)
MS W S MS S S W MS W W MS MS W VW VW W VW
3.518 3.041 2.793 2.490 2.346 2.154 2.032 1.706 1.588 1.528 1.490 1.435 1.408 1.332 1.245 1.224 1.178
h(calc) (A)
222 400 331 422 511 440 442 551 553 800 733 660 555 753 844 755 773
3.519 3.048 2.797 2.488 2.346 2.155 2.032 1.710 1.587 1.524 1.489 1.437 1.408 1.338 1.244 1.225 1.178
5.231k0.003A; c = 8.563f0.005A; c/a = 1.64. 12.189+0.005 A. very strong; S, strong; MS, medium strong; M, medium; MW, medium weak; W, weak; VW, weak.
fore we can tentatively assume that these phases have structures of the Ho,Co, and Th*Ni,, types respectively. The solid solution a-Mn(Yb) was also found in the samples prepared at high about 2 at.% Yb and had a unit cell dimension pressure; it contained a = 8.94 kO.01 A.
4. Conclusion Four intermediate phases can be obtained in the Mn-Yb system at high pressures and temperatures. Their compositions and crystal structures are similar to those obtained in other binary RE-T systems (RE = rare earth; T = Mn, Fe, Ni, Co). It is of interest to discuss the atomic volume and valence of ytterbium metal in these compounds. Wang and Holder [3] concluded that the absence of Yb,Mn,, from the Mn-Yb system under normal conditions suggests that ytterbium tends not to exist in the trivalent state in its alloys with manganese. However, it is well known that, apart from europium and ytterbium, the sizes of
214
TABLE 3 X-ray data for M,Mn,
and Yb,Mn,,
YbdMn3’ Intensity’
d(meas)
hkl
(A)
vs vs MS vs S
vs
2.821 2.724 2.142 1.963 1.636 1.613
MS MS W
1.567 1.463 1.417 1.255 1.157 1.150
MS M VW VW
1.074 1.066 1.017 0.997
VW
VW
vs
220 310 140 500 231 600 430 511 250 521 440 450 442 180 721 820 371 740 380
di(calc)
di(meas)
(A)
(A)
2.833 2.722 2.142 1.963 1.966 1.636 1.614 1.615 1.572 1.464 1.417 1.257 1.159 1.149 1.149 1.071 1.065 1.017 0.997
VW M S S VW MW VW VW VW VW VW VW MW
2.619 2.441 2.127 2.081 1.905 1.869 1.790 1.602 1.535 1.509 1.490 1.368 1.228
hkl
d(calc) (A)
121 300 220 302 123 222 114 124 304 403 142 125 600
2.621 2.451 2.122 2.081 1.909 1.869 1.787 1.607 1.536 1.506 1.486 1.371 1.225
‘a = 11.336+0.005ii; c = 4.029~0.004xi; c/a = 0.36. ba = 8.49kO.01A; c = 7.88~0.01 A; c/a = 0.93. ‘Abbreviations aa defined in Table 2.
RE metals decrease with increasing atomic mass and that this characteristic is apparently associated with the tendency of these metals to exhibit a divalent character. The average atomic volume AAV (defined as the volume of the unit cell divided by the number of atoms present in the cell) of the compounds RE,T, -x also decreases with increasing atomic mass of the RE component provided that T is unchanged. The dependence of the AAV on the atomic mass is shown in Fig. 1 for REMn, (Cl4 and C15) and RE,Mn,, (D8a). Examination of these data shows that the AAVs of YbMn, and Yb,Mn,, lie on the same lines as the other compounds. Therefore we can conclude that ytterbium behaves like other trivalent metals. We now consider the change in volume during the crystallization of the RE,T, _X compounds. This change is not large, and so the AAVs of these phases are located near the additive line connecting the atomic volumes of the pure elements. This does not apply to europium and ytterbium because, as was mentioned above, they are anomalously large. If we assume that ytterbium is trivalent, its atomic volume must be about 29.8 A3 atom-’ instead of the usual 41.28 A3 atom- i. The data in Fig. 2 show that in this case the AAVs of the high pressure phases Yb,Mn,, YbMn,, Yb,Mn,, and YbzMnl, lie near the additive line. The AAVs of the intermediate phases of the systems Yb-Fe, Er-Mn and Er-Co
215
i5b
Yb
I
im
IcdlTb
164
168
iDj IHo IEtlTu
82
i7b
IYb Ilu
“’ M,o.u.
Fig. 1. The dependence of the AAV of REMn, and RE,Mn,, on the atomic mass of the RE element: A, structure type C15; 0, structure type C14; @, structure type D8a; 0, YbMn,; 0, Yb,Mn,,. Fig. 2. The dependence of the AAVs of the intermediate phases of binary RE-T systems (RE = Yb,Er; T s Mn,Fe,Co) on the T content. are included in Fig. 2 for comparison (the unit cell sizes of these phases were taken from refs. 4-6). Therefore we can conclude that high pressures induce a trivalent character in ytterbium.
Acknowledgments The authors are greatly indebted to Mrs. R. F. Aksenova Bushuev for their help with the experimental work.
and Mr. A. V.
References 1 2
3 4 5 6
N. L. Eatough and H. T. Hall, Inorg. Chem., 11(1972) 2608. L. G. Khvostantsev, L. F. Vereshchagin and A. P. Novikov, High Temp. High Pressures, 9 (1977) 637. F. E. Wang and J. P. Holder, Trans. Metall. Sot. AIME, 233(1965) 731. K. N. R. Taylor, A& Phys., 20 (1971) 551. J. F. Cannon, D. L. Robertson and H. T. Hall, Muter. Res. Bull., 7(1972) 5. K. H. J. Buschow, J. Less-Common Met., 26(1972) 329.