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Effects of substitution of CuO by NiS on the superconductivity in YBa2Cu3O7−δ
Journal of Magnetism and Magnetic Materials 104-107 (1992) 547-548 North-Holland
Effects of substitution of CuO by NiS on the superconductivity in YBazCu307_ ~ J. Albino Aguiar a, J.M. Ferreira a, M.T. De Melo a, C. Schettini a, F. Schneider a, M.V.S. Barbosa a, L.R. Madeiro de Melo a, A.C. Pav~o b and J.M. Van Ruitenbeek c a Departamento de Fisica, UFPE, 50739 Recife, PE, Brazil b Departamento de Quimica Fundamental, UFPE, 50739 Recife, PE, Brazil ¢ Kamerlingh Onnes Laboratorium, Rijksuniversiteit te Leiden, Netherlands
In this paper we present X-ray diffraction, resistivity and ac magnetic susceptibility studies of NiS-substituted YBazCu307_ ~ superconductors. A set of samples with nominal composition YBaz[(CuO) 1 x(NiS)x]304_~ were prepared. They show a small increase in Tc and a decrease of the room-temperature (RT) resistivity P300 for small substitution of CuO by NiS. However as the NiS concentration is increased Tc decreases and P300 was higher than that of the undoped sample. The results seem to agree with Pauling's resonating valence bond theory for the high-Tc copper oxides superconductors [1]. This theory predicts an increased Tc due to the great number of the unsynchronized resonances generated as the insulating CuO is substituted by NiS. D i f f e r e n t substitutions in h i g h - Tc s u p e r c o n d u c t o r s Y B a 2 C u 3 0 7 _ ~ have b e e n extensively studied and the effect of different substitutions o n the structural and s u p e r c o n d u c t i n g p r o p e r t i e s have b e e n e x a m i n e d [2]. In particular, w h e n Y has b e e n substituted by rare earths the h i g h - Tc superconductivity is not destroyed by the localized m a g n e t i c m o m e n t s of these ions. Also, it is well k n o w n that the s u p e r c o n d u c t i n g transition temp e r a t u r e T¢ decreases considerably w h e n group VIII, IB a n d l i B m e t a l ions are substituted for Cu ions [3]. In the p r e s e n t study, we have investigated the effects of the doping of this c o m p o u n d s with nickel sulfide. Effects of the substitution of O by S a n d Cu by Ni were r e p o r t e d separately but not the C u O - N i S substitution. Substitution of oxygen by sulfur does not c h a n g e the To, but the p h a s e transition is m u c h s h a r p e r a n d the M e i s s n e r effect is almost c o m p l e t e [4]. O n the o t h e r h a n d , nickel impurities lead to a depression of Tc [5,6]. T o p r o b e the s u p e r c o n d u c t i n g state in the NiS modified m a t e r i a l we p r e p a r e d a series of alloyed s p e c i m e n with the n o m i n a l c o n t e n t x of NiS in the range 0 < x < 0.2. S i n t e r e d samples were p r e p a r e d as follows. A p p r o p r i a t e a m o u n t s of Y203 p o w d e r and BaO, C u O a n d NiS with the n o m i n a l composition Y B a z [ ( C u O ) 1 x(NiS)x]3Oy were g r o u n d e d thoroughly In an agate m o r t a r with an agate pestle. T h e mixtures were t h e n p u t into an a l u m i n a crucible a n d fired in a furnace at 880 ° C for 24 h in air and cooled at a rate of 1 ° C / m i n to 300 ° C. T h e o b t a i n e d materials were reg r o u n d e d . This p r o c e d u r e was r e p e a t e d o n e time. After the firing, the p o w d e r was pressed into pellets of 10 m m d i a m e t e r and 1 - 2 m m thickness. T h e pellets were fired at 930 ° C for 24 h a n d cooled in the same way. This p r o c e d u r e was r e p e a t e d one time. It must be observed that t h e NiS was p r e p a r e d by precipitation of
Ni 2+ in a solution of sodium sulfite and so the precipitate o b t a i n e d is not the conducting form of NiS. T h e pellets were t h e n repulverized, pressed in pellets again, and r e h e a t e d in oxygen a t m o s p h e r e at 930 ° C for 24 h. T h e samples were cooled down at the same rate with a midway a n n e a l i n g at 500 ° C for 18 h. F o r x = 0.01 a sample with NiSO 4 instead of NiS was p r e p a r e d in the same way. CuK,~ radiation was used to X-ray analyse the samples. T h e t e m p e r a t u r e d e p e n d e n c e of dc resistivity was m e a s u r e d by the s t a n d a r d f o u r - p r o b e m e t h o d using a H e closed-cycle refrigerator. T h e c u r r e n t and voltage leads were m a d e of fine c o p p e r wires a t t a c h e d to the samples by silver print. A C susceptibility meas u r e m e n t s were p e r f o r m e d in a v a r i a b l e - t e m p e r a t u r e cryostat on polycrystalline pellet samples. T h e absolute values of the oxygen deficiency fi in these c o m p o u n d s were chemically d e t e r m i n e d by an iodometric titration technique. T h e X-ray diffraction p a t t e r n s for all comp o u n d s investigated show that the observed lines could b e indexed with the o r t h o r h o m b i c unit cell. F u r t h e r more, the a b s e n c e of lines associated with secondary phases, for samples with x < 0.05, indicates that we have single-phase samples. T a b l e 1 summarizes the lattice constants, unit cell volume a n d 6 for some samples. Note t h a t the unit cell volume slightly decreases with x for x_< 0.05, which is consistent with the fact t h a t the ionic radii of Ni is smaller t h a n c o p p e r and indicates t h a t the Ni really substitute for copper. T h e electrical resistivity results for a set of five different c o n c e n t r a t i o n samples with n o m i n a l composition Y B a 2 [ ( C u O ) 1 x(NiS)x]3Oy exhibit a metallic-type behavior. T h e R T resistivity for the x = 0.01 pellet is a factor of 3 less t h e n t h a t of the u n d o p e d sample. F u r t h e r doping increases gradually the R T resistivity until it reaches t h a t of u n d o p e d samples for x = 0.05.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
J. Albino Aguiar et al. / Substitution of CuO by NiS in YBa2Cu30 7 a
548 Table 1 Lattice p a r a m e t e r s [(CuO)
1
xAx]304
and
oxygen
deficiency
of
YBa 2
O0
,~
x
a (3,)
b (3,)
c (3,)
v (3, 3)
a
0 ~) 0.01 b) 1).01 ") 0.03 ~ 0.05 '') 0.2 ")
3.8146 3.815 . . 3.815 3.811 3.812
3.8819 3.878 . 3.877 3.879 3.901
11.670 11.682
172.808 172.785
11.663 11.631 11.671
172.505 171.940 173.555
0.17 0.17 0.18 (I.37
.
-1.0 "c
o
X
X=O03
•
X=02
-2.0
X
-3.0 a) A = NiS; t,) A = NiSO4; c) from ref. [8].
-4.0
T h e s a m p l e with t h e x = 0.2 p r e s e n t s a R T resistivity factor o f 1.5 h i g h e r t h a n t h e x = 0 s a m p l e . Fig. 1 s h o w s t h e t e m p e r a t u r e d e p e n d e n c e o f t h e n o r m a l i z e d resistivity p ( T ) / p ( 3 0 0 K) m e a s u r e by t h e standard four-probe technique. The transition tempera t u r e Tc was t a k e n as t h e o n s e t p o i n t o f t h e transition. O n e sees that s m a l l e r s u b s t i t u t i o n o f C u O by NiS s e e m s to c a u s e a small i n c r e a s e on Tc. F o r x = 0.01 a n d x = 0.03 s a m p l e s , T~ is 93 a n d 92 K, respectively, w h e r e a s t h e u n d o p e d s a m p l e s have a T~ o f 90 K. F o r x = 0.05 and x = 0.2, T~ d r o p s to 88 a n d 80 K, r e s p e c tively, but o n e still sees a metallic b e h a v i o r in t h e n o r m a l state. This in c o n t r a d i c t i o n to that r e p o r t e d by M a e n o et al. [6], w h e n only Cu is s u b s t i t u t e d by Ni. T h e s a m p l e with x = 0.01, a l t h o u g h p r e p a r e d using NiSO4, p r e s e n t e d a R T resistivity by a factor o f 2.5 h i g h e r as c o m p a r e d to t h e x = 0 s a m p l e , b u t still p r e s e n t e d a m e t a l l i c b e h a v i o r a n d a high t r a n s i t i o n 1.0
• oo o • • •o o • • •m • • •
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t e m p e r a t u r e (T c = 93 K). T h e real ( X ' ) p a r t o f t h e ac susceptibility o f x = 0.03 a n d x = 0.2 s a m p l e s as a f u n c t i o n o f t e m p e r a t u r e is s h o w n in fig. 2. T h e s a m p l e with x = 0.03 has a s h a r p T~ a n d a large v o l u m e f r a c t i o n o f s u p e r c o n d u c t o r , w h e r e a s t h e x = 0.2 s a m p l e has a low Tc, a wide transition, a n d a low v o l u m e fraction. T h e resistivity, X-ray, ac susceptibility a n d oxygen c o n t e n t results for t h e x = 0.20 s a m p l e i n d i c a t e that this is a m u l t i p h a s e s a m p l e . This c o n c l u s i o n is c o n f i r m e d by m i c r o s c a n s t u d i e s [7]. T h e s e p r e l i m i n a r y results for small d o p i n g s e e m s to a g r e e with t h e p r e d i c t i o n o f t h e r e s o n a t i n g v a l e n c e b o n d t h e o r y f o r m u l a t e d by P a u l i n g [1]. T h e s t u d i e s to d a t e i n d i c a t e t h e d i r e c t i o n for f u t u r e work. This will i n c l u d e r e s e a r c h to p r e p a r e t h e s a m p l e s with the metallic NiS a n d trying a n o t h e r h e a t a n d oxygen t r e a t m e n t . This is c u r r e n t l y u n d e r way and will b e r e p o r t e d elsewhere.
References
o 06-
• n
I
o
•
• o
0.2
4~ 0
This w o r k was s u p p o r t e d CNPq and FINEP.
to
B'~ •
t 20
•
x n x x{~ xIQA •
• °xk~
8
t i i 60 80 100 120 T(K) Fig. 2. AC susceptibility vs temperature of YBa2[(CuO) I (NiS)x]304 a. 0.0
1;0
2;0
I 250
300
T(K)
Fig. 1. Normalized resistivity vs temperature of YBa2 [(CuO)l x(NiS),]3Oa a. The inset is an enlargement of the transition region.
[1] L. Pauling, Phys. Rev. Lett. 59 (1987) 225. [2] J.T. Markert et al., in: Physical Properties of High Temperature Superconductors, ed. D.M. Ginsberg (World Scientific, Singapore, 1989) p. 265. [3] G. Xiao et al., Phys. Rev. B 35 (1987) 8782. [4] I. Felner, I. Nowik and Y. Yeshurun, Phys. Rev. B 36 (1987) 3923. [5] H. Adrian and S. Nielsen, Europhys. Lett. 5 (1988) 265. [6] Y. Maeno et al., Jpn. J. Appl. Phys. 26 (1987) L774. [7] T. Gortemuller, Kamerling Onnes Laboratorium, private communication. [8] J.M. Tarascon et al., Phys. Rev. B 37 (1988) 7458.
Effects of substitution of CuO by NiS on the superconductivity in YBazCu307_ ~ J. Albino Aguiar a, J.M. Ferreira a, M.T. De Melo a, C. Schettini a, F. Schneider a, M.V.S. Barbosa a, L.R. Madeiro de Melo a, A.C. Pav~o b and J.M. Van Ruitenbeek c a Departamento de Fisica, UFPE, 50739 Recife, PE, Brazil b Departamento de Quimica Fundamental, UFPE, 50739 Recife, PE, Brazil ¢ Kamerlingh Onnes Laboratorium, Rijksuniversiteit te Leiden, Netherlands
In this paper we present X-ray diffraction, resistivity and ac magnetic susceptibility studies of NiS-substituted YBazCu307_ ~ superconductors. A set of samples with nominal composition YBaz[(CuO) 1 x(NiS)x]304_~ were prepared. They show a small increase in Tc and a decrease of the room-temperature (RT) resistivity P300 for small substitution of CuO by NiS. However as the NiS concentration is increased Tc decreases and P300 was higher than that of the undoped sample. The results seem to agree with Pauling's resonating valence bond theory for the high-Tc copper oxides superconductors [1]. This theory predicts an increased Tc due to the great number of the unsynchronized resonances generated as the insulating CuO is substituted by NiS. D i f f e r e n t substitutions in h i g h - Tc s u p e r c o n d u c t o r s Y B a 2 C u 3 0 7 _ ~ have b e e n extensively studied and the effect of different substitutions o n the structural and s u p e r c o n d u c t i n g p r o p e r t i e s have b e e n e x a m i n e d [2]. In particular, w h e n Y has b e e n substituted by rare earths the h i g h - Tc superconductivity is not destroyed by the localized m a g n e t i c m o m e n t s of these ions. Also, it is well k n o w n that the s u p e r c o n d u c t i n g transition temp e r a t u r e T¢ decreases considerably w h e n group VIII, IB a n d l i B m e t a l ions are substituted for Cu ions [3]. In the p r e s e n t study, we have investigated the effects of the doping of this c o m p o u n d s with nickel sulfide. Effects of the substitution of O by S a n d Cu by Ni were r e p o r t e d separately but not the C u O - N i S substitution. Substitution of oxygen by sulfur does not c h a n g e the To, but the p h a s e transition is m u c h s h a r p e r a n d the M e i s s n e r effect is almost c o m p l e t e [4]. O n the o t h e r h a n d , nickel impurities lead to a depression of Tc [5,6]. T o p r o b e the s u p e r c o n d u c t i n g state in the NiS modified m a t e r i a l we p r e p a r e d a series of alloyed s p e c i m e n with the n o m i n a l c o n t e n t x of NiS in the range 0 < x < 0.2. S i n t e r e d samples were p r e p a r e d as follows. A p p r o p r i a t e a m o u n t s of Y203 p o w d e r and BaO, C u O a n d NiS with the n o m i n a l composition Y B a z [ ( C u O ) 1 x(NiS)x]3Oy were g r o u n d e d thoroughly In an agate m o r t a r with an agate pestle. T h e mixtures were t h e n p u t into an a l u m i n a crucible a n d fired in a furnace at 880 ° C for 24 h in air and cooled at a rate of 1 ° C / m i n to 300 ° C. T h e o b t a i n e d materials were reg r o u n d e d . This p r o c e d u r e was r e p e a t e d o n e time. After the firing, the p o w d e r was pressed into pellets of 10 m m d i a m e t e r and 1 - 2 m m thickness. T h e pellets were fired at 930 ° C for 24 h a n d cooled in the same way. This p r o c e d u r e was r e p e a t e d one time. It must be observed that t h e NiS was p r e p a r e d by precipitation of
Ni 2+ in a solution of sodium sulfite and so the precipitate o b t a i n e d is not the conducting form of NiS. T h e pellets were t h e n repulverized, pressed in pellets again, and r e h e a t e d in oxygen a t m o s p h e r e at 930 ° C for 24 h. T h e samples were cooled down at the same rate with a midway a n n e a l i n g at 500 ° C for 18 h. F o r x = 0.01 a sample with NiSO 4 instead of NiS was p r e p a r e d in the same way. CuK,~ radiation was used to X-ray analyse the samples. T h e t e m p e r a t u r e d e p e n d e n c e of dc resistivity was m e a s u r e d by the s t a n d a r d f o u r - p r o b e m e t h o d using a H e closed-cycle refrigerator. T h e c u r r e n t and voltage leads were m a d e of fine c o p p e r wires a t t a c h e d to the samples by silver print. A C susceptibility meas u r e m e n t s were p e r f o r m e d in a v a r i a b l e - t e m p e r a t u r e cryostat on polycrystalline pellet samples. T h e absolute values of the oxygen deficiency fi in these c o m p o u n d s were chemically d e t e r m i n e d by an iodometric titration technique. T h e X-ray diffraction p a t t e r n s for all comp o u n d s investigated show that the observed lines could b e indexed with the o r t h o r h o m b i c unit cell. F u r t h e r more, the a b s e n c e of lines associated with secondary phases, for samples with x < 0.05, indicates that we have single-phase samples. T a b l e 1 summarizes the lattice constants, unit cell volume a n d 6 for some samples. Note t h a t the unit cell volume slightly decreases with x for x_< 0.05, which is consistent with the fact t h a t the ionic radii of Ni is smaller t h a n c o p p e r and indicates t h a t the Ni really substitute for copper. T h e electrical resistivity results for a set of five different c o n c e n t r a t i o n samples with n o m i n a l composition Y B a 2 [ ( C u O ) 1 x(NiS)x]3Oy exhibit a metallic-type behavior. T h e R T resistivity for the x = 0.01 pellet is a factor of 3 less t h e n t h a t of the u n d o p e d sample. F u r t h e r doping increases gradually the R T resistivity until it reaches t h a t of u n d o p e d samples for x = 0.05.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
J. Albino Aguiar et al. / Substitution of CuO by NiS in YBa2Cu30 7 a
548 Table 1 Lattice p a r a m e t e r s [(CuO)
1
xAx]304
and
oxygen
deficiency
of
YBa 2
O0
,~
x
a (3,)
b (3,)
c (3,)
v (3, 3)
a
0 ~) 0.01 b) 1).01 ") 0.03 ~ 0.05 '') 0.2 ")
3.8146 3.815 . . 3.815 3.811 3.812
3.8819 3.878 . 3.877 3.879 3.901
11.670 11.682
172.808 172.785
11.663 11.631 11.671
172.505 171.940 173.555
0.17 0.17 0.18 (I.37
.
-1.0 "c
o
X
X=O03
•
X=02
-2.0
X
-3.0 a) A = NiS; t,) A = NiSO4; c) from ref. [8].
-4.0
T h e s a m p l e with t h e x = 0.2 p r e s e n t s a R T resistivity factor o f 1.5 h i g h e r t h a n t h e x = 0 s a m p l e . Fig. 1 s h o w s t h e t e m p e r a t u r e d e p e n d e n c e o f t h e n o r m a l i z e d resistivity p ( T ) / p ( 3 0 0 K) m e a s u r e by t h e standard four-probe technique. The transition tempera t u r e Tc was t a k e n as t h e o n s e t p o i n t o f t h e transition. O n e sees that s m a l l e r s u b s t i t u t i o n o f C u O by NiS s e e m s to c a u s e a small i n c r e a s e on Tc. F o r x = 0.01 a n d x = 0.03 s a m p l e s , T~ is 93 a n d 92 K, respectively, w h e r e a s t h e u n d o p e d s a m p l e s have a T~ o f 90 K. F o r x = 0.05 and x = 0.2, T~ d r o p s to 88 a n d 80 K, r e s p e c tively, but o n e still sees a metallic b e h a v i o r in t h e n o r m a l state. This in c o n t r a d i c t i o n to that r e p o r t e d by M a e n o et al. [6], w h e n only Cu is s u b s t i t u t e d by Ni. T h e s a m p l e with x = 0.01, a l t h o u g h p r e p a r e d using NiSO4, p r e s e n t e d a R T resistivity by a factor o f 2.5 h i g h e r as c o m p a r e d to t h e x = 0 s a m p l e , b u t still p r e s e n t e d a m e t a l l i c b e h a v i o r a n d a high t r a n s i t i o n 1.0
• oo o • • •o o • • •m • • •
0.8-
•
oa m ~ o~A Ao
•o
06-
~. ~_ 0.4.
A
o a
I
~08O
~
~
I
~11
0
x
I
-" ~-
d~ x
•
o o o
×
I
T(K)
. 1 O0
agencies
D
o.o J , ~. . . . . . 7o 7'~ 80 ~85 ~o 9'~ ~oo lo5 50
by Brazilian
O
D
•
0.4
02
o
0.0
t e m p e r a t u r e (T c = 93 K). T h e real ( X ' ) p a r t o f t h e ac susceptibility o f x = 0.03 a n d x = 0.2 s a m p l e s as a f u n c t i o n o f t e m p e r a t u r e is s h o w n in fig. 2. T h e s a m p l e with x = 0.03 has a s h a r p T~ a n d a large v o l u m e f r a c t i o n o f s u p e r c o n d u c t o r , w h e r e a s t h e x = 0.2 s a m p l e has a low Tc, a wide transition, a n d a low v o l u m e fraction. T h e resistivity, X-ray, ac susceptibility a n d oxygen c o n t e n t results for t h e x = 0.20 s a m p l e i n d i c a t e that this is a m u l t i p h a s e s a m p l e . This c o n c l u s i o n is c o n f i r m e d by m i c r o s c a n s t u d i e s [7]. T h e s e p r e l i m i n a r y results for small d o p i n g s e e m s to a g r e e with t h e p r e d i c t i o n o f t h e r e s o n a t i n g v a l e n c e b o n d t h e o r y f o r m u l a t e d by P a u l i n g [1]. T h e s t u d i e s to d a t e i n d i c a t e t h e d i r e c t i o n for f u t u r e work. This will i n c l u d e r e s e a r c h to p r e p a r e t h e s a m p l e s with the metallic NiS a n d trying a n o t h e r h e a t a n d oxygen t r e a t m e n t . This is c u r r e n t l y u n d e r way and will b e r e p o r t e d elsewhere.
References
o 06-
• n
I
o
•
• o
0.2
4~ 0
This w o r k was s u p p o r t e d CNPq and FINEP.
to
B'~ •
t 20
•
x n x x{~ xIQA •
• °xk~
8
t i i 60 80 100 120 T(K) Fig. 2. AC susceptibility vs temperature of YBa2[(CuO) I (NiS)x]304 a. 0.0
1;0
2;0
I 250
300
T(K)
Fig. 1. Normalized resistivity vs temperature of YBa2 [(CuO)l x(NiS),]3Oa a. The inset is an enlargement of the transition region.
[1] L. Pauling, Phys. Rev. Lett. 59 (1987) 225. [2] J.T. Markert et al., in: Physical Properties of High Temperature Superconductors, ed. D.M. Ginsberg (World Scientific, Singapore, 1989) p. 265. [3] G. Xiao et al., Phys. Rev. B 35 (1987) 8782. [4] I. Felner, I. Nowik and Y. Yeshurun, Phys. Rev. B 36 (1987) 3923. [5] H. Adrian and S. Nielsen, Europhys. Lett. 5 (1988) 265. [6] Y. Maeno et al., Jpn. J. Appl. Phys. 26 (1987) L774. [7] T. Gortemuller, Kamerling Onnes Laboratorium, private communication. [8] J.M. Tarascon et al., Phys. Rev. B 37 (1988) 7458.