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The intermediate phase Nb4Ga5
111
Journal of the Less-Common Metals, 58 (1978) 111 - 113 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
Letter
The intermediate phase Nb4Ga,
M. DRY9 Institute for Low Temperature Katedralny I, 50-950 Wroctaw (Received
November
and Structure (Poland)
Research,
Polish Academy
of Sciences,
Plac
4, 1977)
An intermediate phase with an incongruent melting point of 1300 “C was reported by some authors to occur at the NbeGaS stoichiometry in the Nb-Ga system [ 1 - 31. Our earlier work [4 - 61 confirmed the existence of this phase of unknown crystal structure. The present communication gives the results of a preliminary structure determination obtained on a single crystal. Niobium (purity 99.9%) from H C. Starck Berlin and Ga (purity 99.99%) from Koch Light Lab. were used. Alloys with compositions close to NbdGas (from 43 to 60 wt.% Ga) were prepared by arc melting presintered Nb-Ga powder compacts and by heat treatment in an induction furnace. The arc-melted samples were placed in AlsO3 containers inside a tantalum crucible, remelted in an h.f. furnace under an argon pressure of 0.5 atm (measured at 20 “C), annealed for several hours slightly below 1300 “C!(i.e. below the incongruent melting temperature of Nb,Ga,) and finally slowly cooled to room temperature. The phases occurring in the samples were identified by the X-ray powder diffraction method, using a Guinier focussing camera, Cu K,i radiation and NaCl as an internal standard. Some samples were analysed by using an electron microprobe [ 51. For the structure analysis, very small single crystals were selected from a crushed alloy containing mainly the NbdGas phase and a small amount of NbsGa*. The crystals were examined in a Weissenberg camera. The tetragonal symmetry of the lattice was established and cell dimensions were determined. Using these data, the powder patterns were indexed and the lattice constants, a = 8.381 f 0.002 a and c = 17.081 + 0.004 8, were obtained. In an earlier work on the crystal structure refinement of Nb,Ga, [7] we reported an intermediate phase of unknown structure which was supposed to be NbsGas, as previously reported by various authors [8 - lo]. The present investigations indicate that it was the Nb4Ga, phase, existing in equilibrium with Nb,Ga, . The intermediate phase Nb,Ga, does not seem to have a range of homogeneity, since there was no detectable variation of lattice constants
112
with sample composition. The results of an electron microprobe analysis, given in Table 1, show a very small change in the chemical composition of the Nb4Ga5 phase, indicating that a very narrow homogeneity range is just possible. The X-ray powder diffraction data are given in Table 2. The complete determination of the crystal structure of Nb4Ga5 will be dealt with in further work. TABLE Electron
1 microprobe
Sample compositir (wt.% Ga)
112 211 105 204 220 006 301 205 312 303 224 313 206 304 230 321 216 314 305 323 008 207 400
alloys
Phases present
NbqGag phase composition (at.% Ga)
Nb,GaE,, NbSGab Nb,gGag, NbsGala NbdGag , NbsGa13 NbbGag, NbsGa13
55.1 55.6 55.9 55.6
f t f f
0.5 0.5 0.5 0.5
2
X-ray powder
hkl
data for Nb-Ga
n
43 53 58 60
TABLE
analysis
diffraction
data for NbqGag
I/If)
dabs (A)
d&c (A)
(ohs)
4.89 3.658 3.164 2.989 2.962 2.846 2.756 2.648 2.530 2.508 2.434 2.403 2.355 2.338 2.324 2.303 2.267 2.252 2.163 2.152 2.136 2.109 2.095
4.87 3.661 3.164 2.991 2.963 2.847 2.757 2.648 2.531 2.508 2.434 2.403 2.355 2.338 2.324 2.303 2.267 2.252 2.163 2.152 2.135 2.109 2.095
2 2 2 3 4 1 3 5 8 25 40 2 53 59 100 41 30 44 26 62 11 7 45
hkl 234 118 306 412 403 332 218 422 425 512 2010 2210 329 506 0012 600 3210 526 534 541 3310 536 4011
dabs (A)
&a
I/IQ
(A)
(ohs)
2.0427 2.0090 1.9940 1.9770 1.9662 1.9240 1.8543 1.8301 1.6422 1.6147 1.5824 1.4807 1.4703 1.4447 1.4233 1.3964 1.3763 1.3659 1.3624 1.3054 1.2917 1.2832 1.2474
2.0449 2.0088 1.9939 1.9773 1.9662 1.9245 1.8552 1.8304 1.6430 1.6140 1.5818 1.4798 1.4701 1.4444 1.4234 1.3968 1.3764 1.3655 1.3622 1.3050 1.2920 1.2830 1.2476
4 6 17 3 3 5 5 7 2 8 6 6 6 8 4 12 6 12 26 8 12 5 11
113 1 2 3 4 5 6 7
V. M. Pan and V. I. Latysheva, Metallofizika, 38 (1971) 95. H. G. Meissner and K. Schubert, Z. Metallkd., 56 (1965) 475. J. L. Jorda, R. Fliikiger and J. Muller, J. Less-Common Met., 55 (1977) 249. M. Dry.+.,J. Less-Common Met., 44 (1976) 229. M. Dry& J. Less-Common Met., 52 (1977) 81. M. Dry& J. Less-Common Met., in the press. M. Dry& R. Kubiak and K. Lukaszewicz, Bull. Acad. Pol. Sci., Ser. Sci. Chim., 21 (1973) 901. 8 V. V. Baron, L. F. Myzenkova, E. M. Savitskii and E. J. Gladyshevskii, Zh. Neorg. Khim., 9 (1964) 2170. 9 L. L. Oden and R. E. Siemens, J. Less-Common Met., 14 (1968) 33. 10 P. Fechotte and E. L. Spitz, J. Less-Common Met., 37 (1974) 233.
Journal of the Less-Common Metals, 58 (1978) 111 - 113 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
Letter
The intermediate phase Nb4Ga,
M. DRY9 Institute for Low Temperature Katedralny I, 50-950 Wroctaw (Received
November
and Structure (Poland)
Research,
Polish Academy
of Sciences,
Plac
4, 1977)
An intermediate phase with an incongruent melting point of 1300 “C was reported by some authors to occur at the NbeGaS stoichiometry in the Nb-Ga system [ 1 - 31. Our earlier work [4 - 61 confirmed the existence of this phase of unknown crystal structure. The present communication gives the results of a preliminary structure determination obtained on a single crystal. Niobium (purity 99.9%) from H C. Starck Berlin and Ga (purity 99.99%) from Koch Light Lab. were used. Alloys with compositions close to NbdGas (from 43 to 60 wt.% Ga) were prepared by arc melting presintered Nb-Ga powder compacts and by heat treatment in an induction furnace. The arc-melted samples were placed in AlsO3 containers inside a tantalum crucible, remelted in an h.f. furnace under an argon pressure of 0.5 atm (measured at 20 “C), annealed for several hours slightly below 1300 “C!(i.e. below the incongruent melting temperature of Nb,Ga,) and finally slowly cooled to room temperature. The phases occurring in the samples were identified by the X-ray powder diffraction method, using a Guinier focussing camera, Cu K,i radiation and NaCl as an internal standard. Some samples were analysed by using an electron microprobe [ 51. For the structure analysis, very small single crystals were selected from a crushed alloy containing mainly the NbdGas phase and a small amount of NbsGa*. The crystals were examined in a Weissenberg camera. The tetragonal symmetry of the lattice was established and cell dimensions were determined. Using these data, the powder patterns were indexed and the lattice constants, a = 8.381 f 0.002 a and c = 17.081 + 0.004 8, were obtained. In an earlier work on the crystal structure refinement of Nb,Ga, [7] we reported an intermediate phase of unknown structure which was supposed to be NbsGas, as previously reported by various authors [8 - lo]. The present investigations indicate that it was the Nb4Ga, phase, existing in equilibrium with Nb,Ga, . The intermediate phase Nb,Ga, does not seem to have a range of homogeneity, since there was no detectable variation of lattice constants
112
with sample composition. The results of an electron microprobe analysis, given in Table 1, show a very small change in the chemical composition of the Nb4Ga5 phase, indicating that a very narrow homogeneity range is just possible. The X-ray powder diffraction data are given in Table 2. The complete determination of the crystal structure of Nb4Ga5 will be dealt with in further work. TABLE Electron
1 microprobe
Sample compositir (wt.% Ga)
112 211 105 204 220 006 301 205 312 303 224 313 206 304 230 321 216 314 305 323 008 207 400
alloys
Phases present
NbqGag phase composition (at.% Ga)
Nb,GaE,, NbSGab Nb,gGag, NbsGala NbdGag , NbsGa13 NbbGag, NbsGa13
55.1 55.6 55.9 55.6
f t f f
0.5 0.5 0.5 0.5
2
X-ray powder
hkl
data for Nb-Ga
n
43 53 58 60
TABLE
analysis
diffraction
data for NbqGag
I/If)
dabs (A)
d&c (A)
(ohs)
4.89 3.658 3.164 2.989 2.962 2.846 2.756 2.648 2.530 2.508 2.434 2.403 2.355 2.338 2.324 2.303 2.267 2.252 2.163 2.152 2.136 2.109 2.095
4.87 3.661 3.164 2.991 2.963 2.847 2.757 2.648 2.531 2.508 2.434 2.403 2.355 2.338 2.324 2.303 2.267 2.252 2.163 2.152 2.135 2.109 2.095
2 2 2 3 4 1 3 5 8 25 40 2 53 59 100 41 30 44 26 62 11 7 45
hkl 234 118 306 412 403 332 218 422 425 512 2010 2210 329 506 0012 600 3210 526 534 541 3310 536 4011
dabs (A)
&a
I/IQ
(A)
(ohs)
2.0427 2.0090 1.9940 1.9770 1.9662 1.9240 1.8543 1.8301 1.6422 1.6147 1.5824 1.4807 1.4703 1.4447 1.4233 1.3964 1.3763 1.3659 1.3624 1.3054 1.2917 1.2832 1.2474
2.0449 2.0088 1.9939 1.9773 1.9662 1.9245 1.8552 1.8304 1.6430 1.6140 1.5818 1.4798 1.4701 1.4444 1.4234 1.3968 1.3764 1.3655 1.3622 1.3050 1.2920 1.2830 1.2476
4 6 17 3 3 5 5 7 2 8 6 6 6 8 4 12 6 12 26 8 12 5 11
113 1 2 3 4 5 6 7
V. M. Pan and V. I. Latysheva, Metallofizika, 38 (1971) 95. H. G. Meissner and K. Schubert, Z. Metallkd., 56 (1965) 475. J. L. Jorda, R. Fliikiger and J. Muller, J. Less-Common Met., 55 (1977) 249. M. Dry.+.,J. Less-Common Met., 44 (1976) 229. M. Dry& J. Less-Common Met., 52 (1977) 81. M. Dry& J. Less-Common Met., in the press. M. Dry& R. Kubiak and K. Lukaszewicz, Bull. Acad. Pol. Sci., Ser. Sci. Chim., 21 (1973) 901. 8 V. V. Baron, L. F. Myzenkova, E. M. Savitskii and E. J. Gladyshevskii, Zh. Neorg. Khim., 9 (1964) 2170. 9 L. L. Oden and R. E. Siemens, J. Less-Common Met., 14 (1968) 33. 10 P. Fechotte and E. L. Spitz, J. Less-Common Met., 37 (1974) 233.