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Phase formation and crystallographic investigations of the Dy-Fe-(B,N) system
A A A
Journal of Magnetism and Magnetic Materials 114(1992) 291-294 North-Holland
Phase formation and crystallographic of the Dy-Fe-( B,N) system
‘II
rxz
investigations
, R. Panizzieri a, G. Bocelli b, G. Calestani b, L. Dimesso b, F. Leccabue a, B.E. Watts aT A. Deriu ’ and D. Carrillo d a MASPEC/CNR Institute, via Chiavari 18/a, 43100 Parma, Italy b Centre for Structural Diffractometry / CNR, 43100 Parma, Italy ’ Physics Department, Parma University, 43100 Parma, Italy d Physics Faculty, La Habana University, La Habana, Cuba
The effect of nitrogen on the stability of rare earth: iron 2: 17 and rare earth: iron:metalloid 2: 14: 1 phases has been examined. X ray diffraction and Mijssbauer spectroscopy suggest that a 2: 14: 1 type phase is unlikely to form with nitrogen even in the presence of boron. Thermal analysis found that boron increases the nitrogen absorption significantly.
Correspondence to: Dr. B.E. Watts, MASPEC/CNR Institute, via Chiavari 18/a, 43100 Parma, Italy. Tel.: +39-521-2691; telefax: + 39-521-269206.
Table 1 Amount of absorbed nitrogen for samples treated at 500°C for 6 h in a nitrogen atmosphere Samples
The discoveries of the effects of carbon and more recently nitrogen on the magnetic properties of 2 : 17 rare earth iron alloys [1,2] raising the Curie temperatures and the interest in Sm,Fe,, for possible applications. Dy,Fe,,C is known to exist and in this work the possibility of forming Dy,Fe,,N, using boron to charge compensate the nitrogen has been explored.
2. Alloy preparation and thermal analysis The Dy-Fe alloys were prepared by arc melting followed by a 5 day soak at 900°C in an argon atmosphere and using a pellet of Dy to reduce the evaporation of the rare earth. Each composition was then powdered and (i) used immediately for X-ray (fig. 1) and thermal analysis, (ii) soaked at 500°C for 14 h under N,, (iii> soaked at 930°C for 5 h.
x *0.1
Aw/ w,,,,, (%o)
1. Introduction DyzFei,N, DyzFei4Ba.sN, DyzFei,N, DyzFe17Bo.5N,
+ 6.60 + 7.60 + 6.40 + 8.35
2.6 3.0 2.9 3.8
The powdered samples were treated at 500°C for 6 h under a nitrogen atmosphere in order to form the nitride Dy,Fe,,B,,,N, and Dy,Fe,,N, Table 2 Symmetry and lattice parameters samples examined Sample
for the main phase in the
Symmetry
Lattice parameters Gil
1 Dy&,
2 Dy,Fe,,N,
(500°C) 3 Dy,Fe,,N, (730°C) 4 Dy,Fe,,N, (930°C) 5 Dy,Fe,,N,B,, (930°C) 6 DyaFer4Ba.s 7 DyaFer7Bo,s
0304-8853/92/%05.00 0 1992 - Elsevier Science Publishers B.V. All rights reserved
hexagonal hexagonal hexagonal hexagonal tetragonal tetragonal tetragonal
a
C
8.52 8.55 8.58 8.73 8.72 8.74 8.75
12.51 12.56 12.61 12.81 11.59 11.83 11.58
F. Leccabue et al. / Investigations of the Dy-Fe-(B,N)
292
(where x is the moles of absorbed nitrogen per mole of starting compound). The x values were obtained from thermograms where the percent AW/%tart is time dependent.
system
The values reported in table 1 clearly show an increase in weight indicating that nitrogen is absorbed in quantities in agreement with previously reported results for the Dy-Fe binary alloys but
DyzFelr -___._A
.-___A
h
Jx_L._
-_A-
hAA-
__h
DyzFelrNx 500°C
DyzFevNx
73OT
DyzFelsNr
93O’C
4 Fig. 1. X ray powder patterns recorded using CoKa radiation.
F. Leccabue et al. / Investigations of the @-Fe-(&V)
the absorption was found to be appreciably higher for samples containing boron.
3. X-ray diffraction Indexing of the diffraction pattern was possible on the basis of a tetragonal symmetry for all the samples containing boron. The hexagonal 2 : 17 structure was not observed when boron was present (see sample 7, table 2). Samples 1 and 2, with nominal composition 2 : 14, both gave a pat-
293
system
tern of the hexagonal type. Nitriding at 730°C does not change the phase. When the temperature is raised to 930°C in addition to the hexagonal 2: 17 phase a tetragonal phase (a = 8.61, c = 11.49 A> was detected. Work is in progress to identify this phase. The final three samples all show the tetragonal 2: 14: 1 phase. A quantity of elemental iron is present as an impurity phase in many of the samples examined. In our samples the increase in cell parameters with the inclusion of interstitial nitrogen is not so marked as in some Sm derivatives [2].
5400
5300
5200
5100
5000
P X
j .z
4400
x .2 2 s 82
43ot
42OC
:. .. 2
41OC
-
.:
.kooc
-8
-6
-4
-c
”
z
4
b
6
Velocity (mm/s) Fig. 2. Room temperature Mijssbauer spectra for Dy,Fe,,N, (a) and Dy2Fe,,Bo,,Nx (b). In both spectra the contributions due to metallic iron and to the main intermetallic phase (a) = 2: 17, (b) = 2: 14: 1 are shown (continuous lines).
F. Leccabue et al. / Investigations of the Dy-Fe-(B,N)
294
4. Miissbauer
study
The Miissbauer spectra for samples with nominal composition Dy,Fe,,N, and Dy,Fe,,B,,N, are shown in figs. 2a and b, respectively. The first spectrum could be well fitted on the basis of a 2: 17 structure (four Zeemann sextets with intensity r&tios 6 : 6 : 3 : 2 which account for k, j, g and f iron sublattices). A fifth sextet had to be added to account for the peaks appearing at about f5.5 mm/s. The hyperfine parameters of this sextet, which is evidenced in the figure, are very close to those of metallic iron and its intensity is 6.5% of the total one. The spectrum of the sample containing boron has a totally different shape reminiscent of that of 2: 14 : 1 compounds. We tried thus to fit the spectra using a 2 : 14 : 1 model (six sextets with intensity ratios 4 : 4 : 2 : 2 : 1: 1 for the kl, k2, jl, j2, e and c iron sites). As for the previous spectrum a further sextet was included to account for a possible contribution from metallic iron. This model gives a very good fit for the outer lines of the spectrum, while the four inner lines clearly show an extra intensity (see fig. 2b). The 2: 14: 1 and iron contributions were then subtracted from the total spectrum. The difference spectrum thus obtained shows a structure very close to that of fig. 2a and can therefore be attributed to a 2: 17 phase. The contributions of the three observed phases (2: 14: 1, 2: 17 and iron) are 39, 37 and 24%, respectively.
system
A similar behaviour was observed for the samples of nominal composition Dy,Fe,,N, and Dy,Fe,,B,,5N,. The spectrum of the sample containing boron can be interpreted in terms of a superposition of a 2: 14 contribution (49%) and a contribution due to metallic iron (51%). The presence of boron is essential in stabilising the 2: 14 phase, and the sample without boron has a 2 : 17 structure. The presence of nitrogen in the 2: 14 : 1 and 2 : 17 structures does not produce appreciable variations of the hyperfine parameters of iron.
5. Conclusions
Nitrogen enters the rare earth-iron structures without changing the symmetry of the phases. Boron seems to enhance the absorption of N,. Analysis of the phases suggests that nitrogen is unlikely to enter the 2 : 14 : 1 phase.
References [l] J.M.D. Coey and Hong Sun, J. Magn. Magn. Mater. 87 (1990) L251. [2] M. Katter, J. Wecker and L. Schultz, J. Magn. Magn. Mater. 92 (1990) L14.
Journal of Magnetism and Magnetic Materials 114(1992) 291-294 North-Holland
Phase formation and crystallographic of the Dy-Fe-( B,N) system
‘II
rxz
investigations
, R. Panizzieri a, G. Bocelli b, G. Calestani b, L. Dimesso b, F. Leccabue a, B.E. Watts aT A. Deriu ’ and D. Carrillo d a MASPEC/CNR Institute, via Chiavari 18/a, 43100 Parma, Italy b Centre for Structural Diffractometry / CNR, 43100 Parma, Italy ’ Physics Department, Parma University, 43100 Parma, Italy d Physics Faculty, La Habana University, La Habana, Cuba
The effect of nitrogen on the stability of rare earth: iron 2: 17 and rare earth: iron:metalloid 2: 14: 1 phases has been examined. X ray diffraction and Mijssbauer spectroscopy suggest that a 2: 14: 1 type phase is unlikely to form with nitrogen even in the presence of boron. Thermal analysis found that boron increases the nitrogen absorption significantly.
Correspondence to: Dr. B.E. Watts, MASPEC/CNR Institute, via Chiavari 18/a, 43100 Parma, Italy. Tel.: +39-521-2691; telefax: + 39-521-269206.
Table 1 Amount of absorbed nitrogen for samples treated at 500°C for 6 h in a nitrogen atmosphere Samples
The discoveries of the effects of carbon and more recently nitrogen on the magnetic properties of 2 : 17 rare earth iron alloys [1,2] raising the Curie temperatures and the interest in Sm,Fe,, for possible applications. Dy,Fe,,C is known to exist and in this work the possibility of forming Dy,Fe,,N, using boron to charge compensate the nitrogen has been explored.
2. Alloy preparation and thermal analysis The Dy-Fe alloys were prepared by arc melting followed by a 5 day soak at 900°C in an argon atmosphere and using a pellet of Dy to reduce the evaporation of the rare earth. Each composition was then powdered and (i) used immediately for X-ray (fig. 1) and thermal analysis, (ii) soaked at 500°C for 14 h under N,, (iii> soaked at 930°C for 5 h.
x *0.1
Aw/ w,,,,, (%o)
1. Introduction DyzFei,N, DyzFei4Ba.sN, DyzFei,N, DyzFe17Bo.5N,
+ 6.60 + 7.60 + 6.40 + 8.35
2.6 3.0 2.9 3.8
The powdered samples were treated at 500°C for 6 h under a nitrogen atmosphere in order to form the nitride Dy,Fe,,B,,,N, and Dy,Fe,,N, Table 2 Symmetry and lattice parameters samples examined Sample
for the main phase in the
Symmetry
Lattice parameters Gil
1 Dy&,
2 Dy,Fe,,N,
(500°C) 3 Dy,Fe,,N, (730°C) 4 Dy,Fe,,N, (930°C) 5 Dy,Fe,,N,B,, (930°C) 6 DyaFer4Ba.s 7 DyaFer7Bo,s
0304-8853/92/%05.00 0 1992 - Elsevier Science Publishers B.V. All rights reserved
hexagonal hexagonal hexagonal hexagonal tetragonal tetragonal tetragonal
a
C
8.52 8.55 8.58 8.73 8.72 8.74 8.75
12.51 12.56 12.61 12.81 11.59 11.83 11.58
F. Leccabue et al. / Investigations of the Dy-Fe-(B,N)
292
(where x is the moles of absorbed nitrogen per mole of starting compound). The x values were obtained from thermograms where the percent AW/%tart is time dependent.
system
The values reported in table 1 clearly show an increase in weight indicating that nitrogen is absorbed in quantities in agreement with previously reported results for the Dy-Fe binary alloys but
DyzFelr -___._A
.-___A
h
Jx_L._
-_A-
hAA-
__h
DyzFelrNx 500°C
DyzFevNx
73OT
DyzFelsNr
93O’C
4 Fig. 1. X ray powder patterns recorded using CoKa radiation.
F. Leccabue et al. / Investigations of the @-Fe-(&V)
the absorption was found to be appreciably higher for samples containing boron.
3. X-ray diffraction Indexing of the diffraction pattern was possible on the basis of a tetragonal symmetry for all the samples containing boron. The hexagonal 2 : 17 structure was not observed when boron was present (see sample 7, table 2). Samples 1 and 2, with nominal composition 2 : 14, both gave a pat-
293
system
tern of the hexagonal type. Nitriding at 730°C does not change the phase. When the temperature is raised to 930°C in addition to the hexagonal 2: 17 phase a tetragonal phase (a = 8.61, c = 11.49 A> was detected. Work is in progress to identify this phase. The final three samples all show the tetragonal 2: 14: 1 phase. A quantity of elemental iron is present as an impurity phase in many of the samples examined. In our samples the increase in cell parameters with the inclusion of interstitial nitrogen is not so marked as in some Sm derivatives [2].
5400
5300
5200
5100
5000
P X
j .z
4400
x .2 2 s 82
43ot
42OC
:. .. 2
41OC
-
.:
.kooc
-8
-6
-4
-c
”
z
4
b
6
Velocity (mm/s) Fig. 2. Room temperature Mijssbauer spectra for Dy,Fe,,N, (a) and Dy2Fe,,Bo,,Nx (b). In both spectra the contributions due to metallic iron and to the main intermetallic phase (a) = 2: 17, (b) = 2: 14: 1 are shown (continuous lines).
F. Leccabue et al. / Investigations of the Dy-Fe-(B,N)
294
4. Miissbauer
study
The Miissbauer spectra for samples with nominal composition Dy,Fe,,N, and Dy,Fe,,B,,N, are shown in figs. 2a and b, respectively. The first spectrum could be well fitted on the basis of a 2: 17 structure (four Zeemann sextets with intensity r&tios 6 : 6 : 3 : 2 which account for k, j, g and f iron sublattices). A fifth sextet had to be added to account for the peaks appearing at about f5.5 mm/s. The hyperfine parameters of this sextet, which is evidenced in the figure, are very close to those of metallic iron and its intensity is 6.5% of the total one. The spectrum of the sample containing boron has a totally different shape reminiscent of that of 2: 14 : 1 compounds. We tried thus to fit the spectra using a 2 : 14 : 1 model (six sextets with intensity ratios 4 : 4 : 2 : 2 : 1: 1 for the kl, k2, jl, j2, e and c iron sites). As for the previous spectrum a further sextet was included to account for a possible contribution from metallic iron. This model gives a very good fit for the outer lines of the spectrum, while the four inner lines clearly show an extra intensity (see fig. 2b). The 2: 14: 1 and iron contributions were then subtracted from the total spectrum. The difference spectrum thus obtained shows a structure very close to that of fig. 2a and can therefore be attributed to a 2: 17 phase. The contributions of the three observed phases (2: 14: 1, 2: 17 and iron) are 39, 37 and 24%, respectively.
system
A similar behaviour was observed for the samples of nominal composition Dy,Fe,,N, and Dy,Fe,,B,,5N,. The spectrum of the sample containing boron can be interpreted in terms of a superposition of a 2: 14 contribution (49%) and a contribution due to metallic iron (51%). The presence of boron is essential in stabilising the 2: 14 phase, and the sample without boron has a 2 : 17 structure. The presence of nitrogen in the 2: 14 : 1 and 2 : 17 structures does not produce appreciable variations of the hyperfine parameters of iron.
5. Conclusions
Nitrogen enters the rare earth-iron structures without changing the symmetry of the phases. Boron seems to enhance the absorption of N,. Analysis of the phases suggests that nitrogen is unlikely to enter the 2 : 14 : 1 phase.
References [l] J.M.D. Coey and Hong Sun, J. Magn. Magn. Mater. 87 (1990) L251. [2] M. Katter, J. Wecker and L. Schultz, J. Magn. Magn. Mater. 92 (1990) L14.