- Email: [email protected]
NMR investigation of dilute AlTa alloys
Solid State Communications, Vol. 7, ‘pp.5l—53. 1969.
Pergamon Press.
Printed in Great Britain
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS K. Tompa, F. Tóth and G. Grüner Central Research Institute for Physics, Budapest, Hungary (Received 24 June 1968)
The NMR spectrum of 27Al was studied in cold rolled and annealed high purity Al, resp. Al-based dilute Al—Ta alloy foils. The NMR spectrum parameters differ considerably for the deformed and the annealed samples, this difference is due to the effect of dislocations. The simultaneous effect of impurities and dislocations is not additive. The second moment of the annealed samples depends on the Ta concentration. The wipe-out number characteristic to first order quadrupole effect, n = 1200, can be explained by the existeiice of a virtual bound electron state.
~—---~------~k——. ______
At_TeA; n— 1200
At_TQCR 9DISL. ~ ~M
2 2—h1 G
—
____
____
—
215 ppm (arna
FIG. 1. 27A1 NMR spectrum parameters in cold-rolled and annealed Al and Al—Ta dilute alloy foils. RECENTLY much attention has been paid to the electron states of a transition element in a dilute alloy of a nonmagnetic host metal, but NMR studies of transition metals dissolved in Al have recently been made by Brettel and Heeger.’ The authors do not know about any NMR studies on a 3d transition element in this metal. The alloy Al—Ta was selected because of the relatively substantial solubility of Ta in Al. Starting materials were 5N Al and 3N Ta. The
preparation of the pure Al metal, and the analysis of its residual impurities is described in reference 3. The Ta content of our alloys was 43 and 215 ppm, as determined spectroscopically.
2
51
NMR spectra were taken at room temperature at a frequency of 6 Mc/s on cold rolled (reduction about 70 per cent) and annealed (350~4500C, 2h) foil samples of 20~thickness with the spectrometer, described previously.4 A few measurements were performed between liquid nitrogen
52
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS
and room temperature and at some other frequencies as well. The results are averaged for different orientations, although the anisotropy is but a few per cent. The results are shown in Fig. 1, those data being shown for the deformed samples only, where the reduction in thickness, i.e. the deformation, is approximately the same. The second moment of the annealed samples is 8.2, 8.4 and 9.2 G2 for pure Al, 43 ppm and the 215 ppm alloy respectively. The signal parameters are independent of temperature and the constant magnetic field. The excess second moment measured on the cold rolled samples is due to the dislocations, On the basis of Faulkner’s work5 the dislocation density estimated from the excess moment is 7.5 8 x 109cm2, and is not dependent on the concentration of Ta. The amplitudes of the derivative signals in the deformed samples differ considerably from those in the annealed ones, according to our measurements, not displayed in the Figure, and depend strongly on the amount of deformation, i.e. on the dislocation density. The effects of the impurities and the dislocations are not additive, so the effect of impurities cannot be studied on unannealed samples. —
The second moment of the NMR spectrum measured on the annealed foils increases linearly with the Ta concentration, also as found in the A1Zn system,6 the moment for pure Al is smaller than the data in the literature. ~The amplitude decrease in the annealed samples due to the addition of Ta, which is independent of temperature and magnetic field, is the result of the first order quadrupole effect. The wipe-out number of the satellites, n, was determined from the formula D
7
where D
3
=
D30 (1
—
c)’
3 and D80 are the amplitudes of the de-
Vol.7, No. 1
rivative signals, normalized to satellite contribution in the alloy and in the pure metal respectively, c the concentration. The value thus obtained, n 1200, is very high, if one compares it with values found in the A1Zn, A1MgB AlAg9 systems, but it is in the same order of magnitude, as found in the AlMn, A1Fe alloys.’ The large wipe-out number can be understood by assuming virtual bound electron states localised at the liiipurity site. The impurity gives rise to an oscillating electric-field gradient of the form q(r) Ar~cos(2k~+ q~),where the amplitude A and phase ~ are determined by the host metal and the phase shifts of the conduction electrons scattered on the impurity atom.’0 Because of the resonant scattering of the conduction electrons on the unfilled Sd shell of the Ta atom, the phase shift = Nir/10 is the predominant one, where N gives the number of electrons on the 5d shell. By considering the residual resitivity, 5.4,~ohmat. % as well,” and comparing this value with the residual resistivities of 3d impurities in 12 the value N 3 seems probable. The wipe-out number computed in a similar way as in reference 1. for the dilute A1Ta alloy, assuming resonant scattering and a phase shift ~)2 377/10 is n = 1006, which is in good agreement with the experimental data. =
=
=
=
=
A more precise analysis of the results and their comparison with other measurements will be published later.
Acknowledgements The authors wish to express their thanks to Professors E. Nagy and L. Pal for fruitful discussions, to Drs. R. Vassel and G. Konczos, for the preparation of the samples, to the staff of the Central Laboratory of the Csepel Metallurgical analyses and to Mr. PWorks Bànkifor forthe hischemical technical —
help in the measurements.
REFERENCES 1. 2.
BRETTEL J.M. and 1-IEEGER A.J.,Phys. Rev. 153, 319 (1967). See also FLYNN C.P., RIGNEY D.A. and GARDNER J.A.,Phil. Mag. 15, 1255 (1967). VOL A.E., Structure and Characteristics of the Twin Band System (in Russi”bn) p.467. Fizmatgiz (1959).
Vol.7, No. 1 3.
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS
KOVACS I., TOTH
J.
53
and VASSEL K.R., KFKI Közl. 15, 115 (1967).
4. TOMPA K. and TOTH F. Magy. Fis. Fóly. 11, 177 (1963). 5.
FAULKNER E.A. and HAM P.K., Phil. Mag. 7, 279 (1962).
6. 7.
FERNELIUS N., Magnetic Resonance and Relaxation (Edited by BLINC R.) p. 497. North Holland, Amsterdam (1967). GUTOWSKY H.S. and MC GARVEY B.R., J. chem. Phys. 20, 1472, (1952). SAGALYN H.S. and HOFMANN A.A., Phys. Rev. 127, 68 (1962). FLYNN G.P. and SEYMOUR E.F.W., Proc. phys. Soc. 77, 922 (1961).
8.
ROWLAND T.J., Acta Met. 3, 74 (1955).
9.
TITMAN M. Physics Chem. Solids 23, 318 (1962). PAVLOVSKAYA B.C., Fizika tverd. Tela 6, 2072 (1964).
10.
BLANDIN A. and FRIEDELJ. ,J. Phys. Rod. 21, 689 (1960).
11. 12.
‘TOTH J., Phys. Status Solidi 27 (1968). BOATO G., BUGO M. and RIZZUTO G.,Nuovo Cim. X, 226 (1966); AOKI R. and OHTSUKA T., J. phys. Soc. Japan 23, 955 (1967).
Mi1i oeymeerawM acCne~oaaHWecnex~pa HMP
VA1 a xo~io~—
HoxaTannOli a no~BeprHyToa TenJIooøpaOoTlce aricoxo~acToueaia— uaH~rn a, 000TneTcTaeaao, pa36aaJieHur~x ennaaai A1Ta xa ajxaaauiieaolt ocuone. flapaaeTpu cnexrpa JLiIP Cyll~eOTBeHHo oTJlaqaaT-
en a .~eclopMapoBaaHuIa noi~aeprays~uxTennoao~oøpaOoTlce o6paa~ax, npa~leMo~~iw~an 3goryT 6NT~o6~neHeaNBoa.zLellcTaaeu AacnoEa~alt. Bos.~el~crsze npxuecell a ~aCnoEagaX~ no naJIneTon a~MTaBwili. BTopo~uoaeHT, aaaepennu~ na no~BeprnyTbIxTorI— J1OBO~ oOpaOoTIce o6pa3t~ax, 3aSMCMT OT noH1~eHTpagaa Ta. ZapaicTepIur~ ~nn naa~pynox~noro e~exra Icoac~4ax~xenTramenan
= 1200 HO
MO~CT öum oO~nenenflYTOM npeAnonozeaxn BxpTya~-
OBJIS8HHOPO
s.zenTponnoro 000Tonaxir.
Pergamon Press.
Printed in Great Britain
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS K. Tompa, F. Tóth and G. Grüner Central Research Institute for Physics, Budapest, Hungary (Received 24 June 1968)
The NMR spectrum of 27Al was studied in cold rolled and annealed high purity Al, resp. Al-based dilute Al—Ta alloy foils. The NMR spectrum parameters differ considerably for the deformed and the annealed samples, this difference is due to the effect of dislocations. The simultaneous effect of impurities and dislocations is not additive. The second moment of the annealed samples depends on the Ta concentration. The wipe-out number characteristic to first order quadrupole effect, n = 1200, can be explained by the existeiice of a virtual bound electron state.
~—---~------~k——. ______
At_TeA; n— 1200
At_TQCR 9DISL. ~ ~M
2 2—h1 G
—
____
____
—
215 ppm (arna
FIG. 1. 27A1 NMR spectrum parameters in cold-rolled and annealed Al and Al—Ta dilute alloy foils. RECENTLY much attention has been paid to the electron states of a transition element in a dilute alloy of a nonmagnetic host metal, but NMR studies of transition metals dissolved in Al have recently been made by Brettel and Heeger.’ The authors do not know about any NMR studies on a 3d transition element in this metal. The alloy Al—Ta was selected because of the relatively substantial solubility of Ta in Al. Starting materials were 5N Al and 3N Ta. The
preparation of the pure Al metal, and the analysis of its residual impurities is described in reference 3. The Ta content of our alloys was 43 and 215 ppm, as determined spectroscopically.
2
51
NMR spectra were taken at room temperature at a frequency of 6 Mc/s on cold rolled (reduction about 70 per cent) and annealed (350~4500C, 2h) foil samples of 20~thickness with the spectrometer, described previously.4 A few measurements were performed between liquid nitrogen
52
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS
and room temperature and at some other frequencies as well. The results are averaged for different orientations, although the anisotropy is but a few per cent. The results are shown in Fig. 1, those data being shown for the deformed samples only, where the reduction in thickness, i.e. the deformation, is approximately the same. The second moment of the annealed samples is 8.2, 8.4 and 9.2 G2 for pure Al, 43 ppm and the 215 ppm alloy respectively. The signal parameters are independent of temperature and the constant magnetic field. The excess second moment measured on the cold rolled samples is due to the dislocations, On the basis of Faulkner’s work5 the dislocation density estimated from the excess moment is 7.5 8 x 109cm2, and is not dependent on the concentration of Ta. The amplitudes of the derivative signals in the deformed samples differ considerably from those in the annealed ones, according to our measurements, not displayed in the Figure, and depend strongly on the amount of deformation, i.e. on the dislocation density. The effects of the impurities and the dislocations are not additive, so the effect of impurities cannot be studied on unannealed samples. —
The second moment of the NMR spectrum measured on the annealed foils increases linearly with the Ta concentration, also as found in the A1Zn system,6 the moment for pure Al is smaller than the data in the literature. ~The amplitude decrease in the annealed samples due to the addition of Ta, which is independent of temperature and magnetic field, is the result of the first order quadrupole effect. The wipe-out number of the satellites, n, was determined from the formula D
7
where D
3
=
D30 (1
—
c)’
3 and D80 are the amplitudes of the de-
Vol.7, No. 1
rivative signals, normalized to satellite contribution in the alloy and in the pure metal respectively, c the concentration. The value thus obtained, n 1200, is very high, if one compares it with values found in the A1Zn, A1MgB AlAg9 systems, but it is in the same order of magnitude, as found in the AlMn, A1Fe alloys.’ The large wipe-out number can be understood by assuming virtual bound electron states localised at the liiipurity site. The impurity gives rise to an oscillating electric-field gradient of the form q(r) Ar~cos(2k~+ q~),where the amplitude A and phase ~ are determined by the host metal and the phase shifts of the conduction electrons scattered on the impurity atom.’0 Because of the resonant scattering of the conduction electrons on the unfilled Sd shell of the Ta atom, the phase shift = Nir/10 is the predominant one, where N gives the number of electrons on the 5d shell. By considering the residual resitivity, 5.4,~ohmat. % as well,” and comparing this value with the residual resistivities of 3d impurities in 12 the value N 3 seems probable. The wipe-out number computed in a similar way as in reference 1. for the dilute A1Ta alloy, assuming resonant scattering and a phase shift ~)2 377/10 is n = 1006, which is in good agreement with the experimental data. =
=
=
=
=
A more precise analysis of the results and their comparison with other measurements will be published later.
Acknowledgements The authors wish to express their thanks to Professors E. Nagy and L. Pal for fruitful discussions, to Drs. R. Vassel and G. Konczos, for the preparation of the samples, to the staff of the Central Laboratory of the Csepel Metallurgical analyses and to Mr. PWorks Bànkifor forthe hischemical technical —
help in the measurements.
REFERENCES 1. 2.
BRETTEL J.M. and 1-IEEGER A.J.,Phys. Rev. 153, 319 (1967). See also FLYNN C.P., RIGNEY D.A. and GARDNER J.A.,Phil. Mag. 15, 1255 (1967). VOL A.E., Structure and Characteristics of the Twin Band System (in Russi”bn) p.467. Fizmatgiz (1959).
Vol.7, No. 1 3.
NMR INVESTIGATION OF DILUTE Al—Ta ALLOYS
KOVACS I., TOTH
J.
53
and VASSEL K.R., KFKI Közl. 15, 115 (1967).
4. TOMPA K. and TOTH F. Magy. Fis. Fóly. 11, 177 (1963). 5.
FAULKNER E.A. and HAM P.K., Phil. Mag. 7, 279 (1962).
6. 7.
FERNELIUS N., Magnetic Resonance and Relaxation (Edited by BLINC R.) p. 497. North Holland, Amsterdam (1967). GUTOWSKY H.S. and MC GARVEY B.R., J. chem. Phys. 20, 1472, (1952). SAGALYN H.S. and HOFMANN A.A., Phys. Rev. 127, 68 (1962). FLYNN G.P. and SEYMOUR E.F.W., Proc. phys. Soc. 77, 922 (1961).
8.
ROWLAND T.J., Acta Met. 3, 74 (1955).
9.
TITMAN M. Physics Chem. Solids 23, 318 (1962). PAVLOVSKAYA B.C., Fizika tverd. Tela 6, 2072 (1964).
10.
BLANDIN A. and FRIEDELJ. ,J. Phys. Rod. 21, 689 (1960).
11. 12.
‘TOTH J., Phys. Status Solidi 27 (1968). BOATO G., BUGO M. and RIZZUTO G.,Nuovo Cim. X, 226 (1966); AOKI R. and OHTSUKA T., J. phys. Soc. Japan 23, 955 (1967).
Mi1i oeymeerawM acCne~oaaHWecnex~pa HMP
VA1 a xo~io~—
HoxaTannOli a no~BeprHyToa TenJIooøpaOoTlce aricoxo~acToueaia— uaH~rn a, 000TneTcTaeaao, pa36aaJieHur~x ennaaai A1Ta xa ajxaaauiieaolt ocuone. flapaaeTpu cnexrpa JLiIP Cyll~eOTBeHHo oTJlaqaaT-
en a .~eclopMapoBaaHuIa noi~aeprays~uxTennoao~oøpaOoTlce o6paa~ax, npa~leMo~~iw~an 3goryT 6NT~o6~neHeaNBoa.zLellcTaaeu AacnoEa~alt. Bos.~el~crsze npxuecell a ~aCnoEagaX~ no naJIneTon a~MTaBwili. BTopo~uoaeHT, aaaepennu~ na no~BeprnyTbIxTorI— J1OBO~ oOpaOoTIce o6pa3t~ax, 3aSMCMT OT noH1~eHTpagaa Ta. ZapaicTepIur~ ~nn naa~pynox~noro e~exra Icoac~4ax~xenTramenan
= 1200 HO
MO~CT öum oO~nenenflYTOM npeAnonozeaxn BxpTya~-
OBJIS8HHOPO
s.zenTponnoro 000Tonaxir.