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57MÖSSBAUER STUDY OF Th7Fe3 AND THE HYDRIDE Th7Fe3H14.2
P. Viccaro, G. Shenoy, B. Dunlap, D. Westlake, S. Malik, W. Wallace
To cite this version:
P. Viccaro, G. Shenoy, B. Dunlap, D. Westlake, S. Malik, et al.. 57MÖSSBAUER STUDY OF Th7Fe3
AND THE HYDRIDE Th7Fe3H14.2. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-157-C2-
158. �10.1051/jphyscol:1979255�. �jpa-00218653�
57MOSSBAUER STUDY OF Th Fe3 AND THE HYDRIDE T l ^ F ^ H ^ *
P.J. Viccaro , G.K. Shenoy, B.D. Dunlap, D.G. 'Westlake, S.K. Malik* and W.E. Wallace*
Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
^University of Pittsburgh, Pittsburgh, PA 15213, U.S.A.
Abstract.- Th7Fe3 is known to be a Pauli paramagnet and to undergo a superconducting transition at 1.86 K. In contrast, its saturated hydride Th7Fe3H3o shows magnetic ordering. For the stable hydri- de considered here of intermediate concentration ThyFesHm.2, the 5 Fe saturated hyperfine field to estimate to be approximately 20 kG. A positive isomer shift of 0.30+0.02 mm/s at 300 K relative to ThyFe3 would be consistent with an increase of d character at the Fe site induced by hydrogen.
1 . Introduction.- The intermetallic compound Tti7Fe3 readily absorbs hydrogen at room temperature. The hydride formed at saturation has the approximate composition Th7Fe3H3o with a hydrogen equilibrium pressure of <0.01 atmospheres /l/. It has been re- ported chat while Th7Fe3 is a Pauli paramagnetic and superconducting below 1.86 K /2/, its hydride exhi- bits magnetic ordering /3,4/. Magnetization results for the saturated hydride show a moment of 4.2 y_
a
per formula unit and a transition temperature above 330 K /5/. In this work, we present 57Fe Mossbauer and X-ray diffraction results for the stable inter- mediate concentration hydride Th7Fe3Hm.2.
2. Experimental.- Debye-Scherrer X-ray diffraction patterns taken of the Th7Fe3 showed d values which were consistent with the DIO2 hexagonal structure reported /6/ for this phase (a = 9.823 A, c = 6.211 A ) . No other phases were detected.
The hydride was formed in a system of known volume using 99.999% hydrogen at pressures above one atmosphere. The amount of hydrogen absorbed was de- termined by monitoring the pressure. This measure- ment yielded Tti7Fe3H with n - 30, in agreement with previous studies /l/. However, a subsequent volume- tric analysis for the hydrogen content of a portion of the sample yielded n = 14.2 + 0.2. This differen- ce indicates that the hydride formed initially, lost hydrogen. Two sets of X-ray diffraction data, des- cribed below, taken well before and after the volu-
metric analysis, showed the same diffraction pat- terns, indicating that the hydride Th7Fe3Hm.2 remai- ned stable during the time the S7Fe Mossbauer mea- surements were made. The two different values for n could be related to the affinity of elemental Th for hydrogen as seems to be the case for La HI. That is the Tti7Fe3H3 0 initially formed at saturation with hydrogen gas, may correspond to ThuHis. On the other hand, Tl^FesHm. 2, which presumably is a decomposi- tion product of the saturated hydride, would appro- ximately correspond to TI1H2 • The implications of these two values for the hydrogen content however, require further experimental investigations.
X-ray analysis of Th7Fe3Hm.2 with Cu K radia- tion and a Ni filter revealed broader reflections than those observed for Th7Fe3. The three strongest reflections have d values of 3.23 (strong), 1.86
o
(medium), and 1.68 A (medium). Although there were too few reflections to permit a reliable structure determination, these d values, along with the others observed, would be consistent with a general struc- ture type equivalent to that of Th7Fe3. A tentative identification of the hydride structure (relative to the metal atoms) would be an expanded version of
o
the Th7Fe3 lattice with a- 10.8 A and c/a - 0.63.
3. Results and discussion.- The 57Fe Mossbauer spec- tra for Th7Fe3 as a function of temperature show on- ly the presence of a quadrupole interaction with a doublet splitting of 0.49 ± 0.02 mm/s and an isomer shift relative to Fe metal of -0.22 + 0.02 mm/s at 300 K. The spectrum at 300 K is1 shown in figure la.
The spectra for the hydride obtained at 300 K Work supported by the U.S. Department of Energy.
On leave from the Instituto de Fisica, UFRGS, Porto Alegre, Brazil.
JOURNAL DE PHYSIQUE Colloque Cl, supplément au n° 3, Tome 40, mars 1979, page C2-157
Résumé.- Th7Fe3 est un système paramagnétique de Pauli et est supraconducteur au-dessous de 1.86 K.
Par contre, l'hydrure saturé Tti7Fe3H3o présente un ordre magnétique. Pour l'hydrure stable de con- centration intermédiaire Th7Fe3Hii,.2 que nous considérons ici, le champ hyperfin à saturation au site de 57Fe est d'environ 20 kG. Un déplacement isomérique positif de 0,30 +. 0,02 mm/s à 300 K par rapport à Th7Fe3 serait en accord avec une augmentation du caractère d au site de Fe causé par la présence d'hydrogène.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979255
c2-158 JOURNAL DE PHYSIQUE
(Fig. Ib) and above consist of an asymmetric doublet with a separation of 0.42 k 0.03 mm/s. At 77 K and 4.2 K (Figs Ic and Id respectively), the spectra broaden and become unresolved. Because of the lack of resolution in the spectra, no conclusive infor- mation could be deduced concerning the specific nature of the magnetic interaction or transition temperature. However, if one assumes that a magne- tic interaction is responsible for the broadening at low temperature, then the data indicate a satu- rated hyperfine field of approximately 20 kG for
5 7 ~ e .
Fig. 1 : 57~6ssbauer spectra of a) Th7Fes at 300 K, and Th7Fe3H14.2 at b) 300 K, c) 77 K d) 4.2 K.
This value for the hyperfine field is confir- med by experiments on the hydride in an external ma- gnetic field of 74 kOe. The spectrum in this case at 4.2 K shows a distribution of hyperfine fields.
The maximum and minimum fields encountered were on the order of 64 kG and 50 kG respectively. If bhe hyperfine field is taken to be opposite in sign to the applied field, as indicated by the data, then this measurement places its value between 10 kG and 25 kG in agreement with the zero field data.
If a simple scaling between the hyperfine field and magnetic moment on Fe is assumed, then the resulting moment is approximately 0.2 pB per Fe for Th7Fe3Hlk.z. This value is substantially lower than the one reported for the saturated hydride,
Th7Fe3H30 of 1.4 pB per Fe /5/.
Finally, the isomer shift at 300 K shows a positive change of 0.30
+
0.02 mm/s for the hydride relative to Th7Fes. This positive change in isomer shift, coupled with the onset of a magnetic interac- tion for the hydride, would be consistent with an increase in d-like character on Fe induced by the presence of hydrogen in the Th7Fes structure. Fur- thermore, the presence of a magnetic interaction in the intermedcare concentration hydride would perhaps destroy the superconducting state in Th7Fe3 as is postulated for the saturated hydride Th7Fe3H30.Work at the University of Pittsburgh was assis- ted by a grant from the Army Research Office.
References
/I/ Buschow, K.H.J., Van Mal, H.H. and Miedema, A.R., J. Less-Common Metals
42
(1975) 163./2/ Matthias, B.T., Compton, V.B. and Corenzwit, E., Phys. Chem. Solids
2
(1961) 130./3/ Malik, S.K., Takeshita, T. and Wallace, W.E., Solid State Commun.
23
(1977) 599./4/ Wallace, W.E., Malik, S.K., Takeshita, T., San- kar, S.G., and Gualtieri, D.M., J. Appl. Phys.
49 (1978) 1486.
-
/5/ Malik, S.K., Wallace, W.E. and Takeshita, T., to be published.
/6/ Florio, J.V., Baenziger, N.C. and Rundle, R.E., Acta. Cryst. Carnb.
9
(1956) 367./7/ Oesterreicher, H., Clinton J. and Bittner, H., Mat. Res. Bull.
