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Superconductivity and electronic structure of V-solid solutions with 3d-, 4d- and 5d-metals
Physica 1078 (1981) 469-470 North-Holland Publishing Company
IB l
SUPERCONDUCTIVITY AND ELECTRONIC STRUCTURE OF V - SOLID SOLUTIONS WITH 3d-, 4d- AND 5d-METALS H.R. Khan, Ch.J. Raub Forschungsinstitut fur Edelmetalle und Metallchemie, D-7070 Schw~blsch Gm~nd, Germany W. D~umer, K. LHders, H. Riesemeier, G. Roth Institut fHr Atom- und FestkSrperphysik, Frele Universit~t Berlin D-tO00 Berlin 33, Germany
Superconducting transition temperatures, Tc, 51~ Knight shift,K, and the resistivity, p, of solid solutions of V (Vo.gX0.1, X = C r , Mn, Nb, Mo, Pd, Ta, Re, Pt and Au) are measured. The maxima in Knight shift for the 4d and 5d solutes exist for an e/a ratio of about 5.2. The normal state resistivity, Pn, increases with decreasing T c. The T c values are related to the d-electron density of states, Nd(EF).
I. INTRODUCTION
technique.
The depression of T c in some of the solid solutions of V with the 3d, 4d and 5d elements as solutes is explained by changes in the electron concentration by some investigators [I-3]. From the T c and specific heat measurements on a series of transition metals and alloys, Morin and Maita [4] concluded that T c depends upon the density of states in the d-band. Devos [5] and Panissod [6] measured the magnetic suscpetibility, Knight shift and the relaxation rate of Vsolid solutions with the transition metals as solutes and also the intermetallic compounds and showed that the magnetic susceptibility is mainly orbital whereas the variation of the susceptibility is due to the d-part. From the measurements of Tc, Knight shift, relaxation time and magnetic susceptibility of some A-15 compounds of V and a series of the Mo-V solid solutions it was concluded that T c strongly depends on the delectron density of states, Nd(E F) [7-9].
3. RESULTS AND DISCUSSION
In this paper measurements of the superconducting transition temperature, Knight shift and resistivity on well characterized V-solid solutions containing 10 at.% of some 3d, 4d and 5d elements as solutes are reported. 2. EXPERIMENTAL The b.c.c, solid solutions of V containing 10 at.% of 3d, 4d and 5d elements as solutes were prepared by arc melting in argon atmosphere and were homogenized in vacuum by heat treatments at different temperatures. The lattice parameters of these solid solutions were determined by Xray diffraction using Cu-K~-radiation and the homogeneity was checked by optical metallography. All the samples were found to be metallographically homogeneous except the Vo.gPto. I and Vo.9Reo. I alloys which contain a small amount of a second phase. 51V Knight shifts were measured at 4.2 K with a cw spectrometer. The T c measurements were made inductively using a carbon glass thermometer with an accuracy of 0 . 1 K . The resistivity measurements were made on samples of known dimensions obtained from the spark cutter using four probe method and a.c.
0378.4363/81/0000-0000/$02.50
© Nonh-HoUand Publi~ingCompany
The T c values and the Knight shifts at 4.2 K as a function of e/a for the V-solid solutions with the 3d, 4d and 5d elements as solutes are plotted in Fig. I. The T c value drops sharply with Cr and Mn as solutes a~ shown in Fig. la. The Tc values of V0.9Cr0. I and V0.gMn0. I are 2.8 and 2.0 K, respectively. A T c value of 3 . 2 1 K for Vo.9Cro. I has been reported by Andres et al. [10]. For the 4d elements as solutes, T c as a function of e/a is plotted in Fig. lb. T c also decreases after dissolving the 4d elements in V from the left to the right of the periodic table. For the V0.9Pdo. I, the T c value is below 1.5 K. No T c value of this alloy is available in literature but a T c value of 0.082 K for the A15 phase V3Pd compound has been reported by Hein et al. [11]. For the 5d elements as solutes, Re, Pt and Au the T c values are below 1.5 K. The initial decrease in T c corresponds to an increase of the Knight shifts for all the V-solid solutions with 3d, 4d and 5d elements as solutes. The K value of V is 0.570% and after dissolving 10 at.% of Cr and Hn, K increases to 0.606%. The variation of K for the 4d solutes shows a maxlmu~ Similarly the Knight shift variation of 5d solutes also shows a maximum located at an e/a ratio of ,,.,5.2. The contributions to the total Knight shift of 51V in V metal are caused by the s-electrons and the orbital and the spin contribution of the 3d electrons. The tota~ Knight shift can be written as K = K s + ( - K d) + K o r b (I) where K d is related to the d-electron density of states Nd(E F) via the d-part of the magnetic susceptibility, Xd, 2
X d " 2~ B N d ( E F ) / ( 1 - ~ )
,
where ~ - N(EF)~c. N(E F) is the total density of states and V c is an effective coulomb potential [13]. 469
470
REFERENCES [I] K
~Dn
[2]
Cr•
n
/,
O.6O
0.59
/
./
Knight shift at /..2K Normal state o resistivity. Pn
•
0.58 0.57
Tc
.o~
.. f " ~
" Tc v Tc <
[3] 50-
[4] 40-
[5]
30-
1.5K
[6] [7]
e"
,
,
,
b
20
70~
[8]
0.60 0.59
"~...
..~.~
[9]
50"
0.58 t
0.57
!
/.0-
[10]
9~fi~
,
,
,
c
0.62
~ ~
0.61 0.60
.. t
/P 0I'
~t\
30
100-
[11]
80-
[12]
60-
2
0.59 0.58
Fig. I.
o~.I"5.0
, 5.2
elo
, 5.4
, 20 5.6
Variation of T c, normal state resistivity, Pn, and Knight shift K at 4.2 K as a function of e/a.
When solid solutions of V are formed with the 3d, 4d and 5d elements, then the number of delectrons changes and hence the d-electron density of states. According to equation (I), a maximum in K implies a minimum in Kd and the delectro~ density of states. For all the solid solutions of 3d, 4d and 5d elements, a maximum in K corresponds to the very low superconducting transition temperatures which implies that the d-electrons and the d-electron density of states influences the superconductivity directly. These data also agree with the correlation between T c and e/a predicted by Matthias [14]. As also shown in fig. I the resistivity Pn increases with increasing e/a ratio for the 3d-, 4d- and 5d-solutes. Since Pn is roughly proportional to I/N(E F) this indicates a decrease of N(E F) with the e/a ratio which agrees with the Knight shift behaviour up to e/a ratios of about 5.2. Further T c measurements at temperatures below 1.5 K are in preparation.
[13] [14]
Mueller, J., Helv. Phys. Acta, 32 (1959) 141. Bucher, E., Busch, G. and Mueller, J., Helv. Phys. Acta 32 (1959) 318. Hulm, J.K. and Blaugher, R.D., Phys. Rev. 123 (1961) 1569. Morin, F.J. and Maita, J.P., Phys. Rev. 129 (1963) 1115.
Devos, J . , J . Phys. Chem. Solids 33 (1972) 31. Panissod, P . , J. Phys. F4 (1974) 484. Gevers, A., Poulis, N.J., Khan, H.R. and Raub, Ch.J., LT (15) (1978) C6-404. Wulffers, L.A.G.M., Frljters, G.A.M., van Shie, C.A., Klassen, T.O., Poulis, N.J., Khan, H.R. and Raub, Ch.J., Physica, 93B
(1978) 180. Khan, H.R., Koebler, U., Lueders, K., Raub, Ch.J. and Szuecs, Z., J. de Physique, Colloque C6, supplement au no. 8, Tom 39 (1978) C6-465. Andres, K., Bucher, E., Malta, J.P. and Sherwood, R.C., Phys. Rev. 178 (1969) 702. Hein, R.A., Cox, J.E., Blaugher, R.D. and Waterstrat, R.M., Solid State Commun., 7 (1969) 381. Corsan, J.M. and Cook, A.J., Phys. Stat. Solidi, 40 (1970) 657. Ganguly, B.N., Phys. Rev. B8 (1973) 1055. Matthias, B.T., Progress in Low Temperature Physics (Interscience, New York) 1957 vol. II.
IB l
SUPERCONDUCTIVITY AND ELECTRONIC STRUCTURE OF V - SOLID SOLUTIONS WITH 3d-, 4d- AND 5d-METALS H.R. Khan, Ch.J. Raub Forschungsinstitut fur Edelmetalle und Metallchemie, D-7070 Schw~blsch Gm~nd, Germany W. D~umer, K. LHders, H. Riesemeier, G. Roth Institut fHr Atom- und FestkSrperphysik, Frele Universit~t Berlin D-tO00 Berlin 33, Germany
Superconducting transition temperatures, Tc, 51~ Knight shift,K, and the resistivity, p, of solid solutions of V (Vo.gX0.1, X = C r , Mn, Nb, Mo, Pd, Ta, Re, Pt and Au) are measured. The maxima in Knight shift for the 4d and 5d solutes exist for an e/a ratio of about 5.2. The normal state resistivity, Pn, increases with decreasing T c. The T c values are related to the d-electron density of states, Nd(EF).
I. INTRODUCTION
technique.
The depression of T c in some of the solid solutions of V with the 3d, 4d and 5d elements as solutes is explained by changes in the electron concentration by some investigators [I-3]. From the T c and specific heat measurements on a series of transition metals and alloys, Morin and Maita [4] concluded that T c depends upon the density of states in the d-band. Devos [5] and Panissod [6] measured the magnetic suscpetibility, Knight shift and the relaxation rate of Vsolid solutions with the transition metals as solutes and also the intermetallic compounds and showed that the magnetic susceptibility is mainly orbital whereas the variation of the susceptibility is due to the d-part. From the measurements of Tc, Knight shift, relaxation time and magnetic susceptibility of some A-15 compounds of V and a series of the Mo-V solid solutions it was concluded that T c strongly depends on the delectron density of states, Nd(E F) [7-9].
3. RESULTS AND DISCUSSION
In this paper measurements of the superconducting transition temperature, Knight shift and resistivity on well characterized V-solid solutions containing 10 at.% of some 3d, 4d and 5d elements as solutes are reported. 2. EXPERIMENTAL The b.c.c, solid solutions of V containing 10 at.% of 3d, 4d and 5d elements as solutes were prepared by arc melting in argon atmosphere and were homogenized in vacuum by heat treatments at different temperatures. The lattice parameters of these solid solutions were determined by Xray diffraction using Cu-K~-radiation and the homogeneity was checked by optical metallography. All the samples were found to be metallographically homogeneous except the Vo.gPto. I and Vo.9Reo. I alloys which contain a small amount of a second phase. 51V Knight shifts were measured at 4.2 K with a cw spectrometer. The T c measurements were made inductively using a carbon glass thermometer with an accuracy of 0 . 1 K . The resistivity measurements were made on samples of known dimensions obtained from the spark cutter using four probe method and a.c.
0378.4363/81/0000-0000/$02.50
© Nonh-HoUand Publi~ingCompany
The T c values and the Knight shifts at 4.2 K as a function of e/a for the V-solid solutions with the 3d, 4d and 5d elements as solutes are plotted in Fig. I. The T c value drops sharply with Cr and Mn as solutes a~ shown in Fig. la. The Tc values of V0.9Cr0. I and V0.gMn0. I are 2.8 and 2.0 K, respectively. A T c value of 3 . 2 1 K for Vo.9Cro. I has been reported by Andres et al. [10]. For the 4d elements as solutes, T c as a function of e/a is plotted in Fig. lb. T c also decreases after dissolving the 4d elements in V from the left to the right of the periodic table. For the V0.9Pdo. I, the T c value is below 1.5 K. No T c value of this alloy is available in literature but a T c value of 0.082 K for the A15 phase V3Pd compound has been reported by Hein et al. [11]. For the 5d elements as solutes, Re, Pt and Au the T c values are below 1.5 K. The initial decrease in T c corresponds to an increase of the Knight shifts for all the V-solid solutions with 3d, 4d and 5d elements as solutes. The K value of V is 0.570% and after dissolving 10 at.% of Cr and Hn, K increases to 0.606%. The variation of K for the 4d solutes shows a maxlmu~ Similarly the Knight shift variation of 5d solutes also shows a maximum located at an e/a ratio of ,,.,5.2. The contributions to the total Knight shift of 51V in V metal are caused by the s-electrons and the orbital and the spin contribution of the 3d electrons. The tota~ Knight shift can be written as K = K s + ( - K d) + K o r b (I) where K d is related to the d-electron density of states Nd(E F) via the d-part of the magnetic susceptibility, Xd, 2
X d " 2~ B N d ( E F ) / ( 1 - ~ )
,
where ~ - N(EF)~c. N(E F) is the total density of states and V c is an effective coulomb potential [13]. 469
470
REFERENCES [I] K
~Dn
[2]
Cr•
n
/,
O.6O
0.59
/
./
Knight shift at /..2K Normal state o resistivity. Pn
•
0.58 0.57
Tc
.o~
.. f " ~
" Tc v Tc <
[3] 50-
[4] 40-
[5]
30-
1.5K
[6] [7]
e"
,
,
,
b
20
70~
[8]
0.60 0.59
"~...
..~.~
[9]
50"
0.58 t
0.57
!
/.0-
[10]
9~fi~
,
,
,
c
0.62
~ ~
0.61 0.60
.. t
/P 0I'
~t\
30
100-
[11]
80-
[12]
60-
2
0.59 0.58
Fig. I.
o~.I"5.0
, 5.2
elo
, 5.4
, 20 5.6
Variation of T c, normal state resistivity, Pn, and Knight shift K at 4.2 K as a function of e/a.
When solid solutions of V are formed with the 3d, 4d and 5d elements, then the number of delectrons changes and hence the d-electron density of states. According to equation (I), a maximum in K implies a minimum in Kd and the delectro~ density of states. For all the solid solutions of 3d, 4d and 5d elements, a maximum in K corresponds to the very low superconducting transition temperatures which implies that the d-electrons and the d-electron density of states influences the superconductivity directly. These data also agree with the correlation between T c and e/a predicted by Matthias [14]. As also shown in fig. I the resistivity Pn increases with increasing e/a ratio for the 3d-, 4d- and 5d-solutes. Since Pn is roughly proportional to I/N(E F) this indicates a decrease of N(E F) with the e/a ratio which agrees with the Knight shift behaviour up to e/a ratios of about 5.2. Further T c measurements at temperatures below 1.5 K are in preparation.
[13] [14]
Mueller, J., Helv. Phys. Acta, 32 (1959) 141. Bucher, E., Busch, G. and Mueller, J., Helv. Phys. Acta 32 (1959) 318. Hulm, J.K. and Blaugher, R.D., Phys. Rev. 123 (1961) 1569. Morin, F.J. and Maita, J.P., Phys. Rev. 129 (1963) 1115.
Devos, J . , J . Phys. Chem. Solids 33 (1972) 31. Panissod, P . , J. Phys. F4 (1974) 484. Gevers, A., Poulis, N.J., Khan, H.R. and Raub, Ch.J., LT (15) (1978) C6-404. Wulffers, L.A.G.M., Frljters, G.A.M., van Shie, C.A., Klassen, T.O., Poulis, N.J., Khan, H.R. and Raub, Ch.J., Physica, 93B
(1978) 180. Khan, H.R., Koebler, U., Lueders, K., Raub, Ch.J. and Szuecs, Z., J. de Physique, Colloque C6, supplement au no. 8, Tom 39 (1978) C6-465. Andres, K., Bucher, E., Malta, J.P. and Sherwood, R.C., Phys. Rev. 178 (1969) 702. Hein, R.A., Cox, J.E., Blaugher, R.D. and Waterstrat, R.M., Solid State Commun., 7 (1969) 381. Corsan, J.M. and Cook, A.J., Phys. Stat. Solidi, 40 (1970) 657. Ganguly, B.N., Phys. Rev. B8 (1973) 1055. Matthias, B.T., Progress in Low Temperature Physics (Interscience, New York) 1957 vol. II.