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Superconductivity of quenched Y1Ba2Cu3O7−x ceramic phases
Solid State Communications, Vol 67, No 7, pp 713-715, 1988 Printed in Great Britain
0038-1098/88 $3 O0 + O0 Pergamon Press plc
S U P E R C O N D U C T I V I T Y O F Q U E N C H E D Yl Ba2Cu307-x C E R A M I C PHASES V F Degtyareva, O V Zharikov, B G Karepov, A M Kokotln, D N Mogllyansky, R K Nlkolaev, N S Sldorov and V Sh Shekhtman Institute of Solid State Physics, Ac Scl USSR Chernogolovka Moscow obl 142432, USSR
(Received 8 Aprd 1988 by V M Agranovwh) An investigation has been carrrled out of how heating in oxygen atmosphere followed by quenching affects the structure and superconducting properties Y~BaECUjO7_, ceramic samples It is shown that the critical temperature of the superconducting transition, Tc, is a non-monotonous function of the quenching temperature, T o Samples subjected to an abrupt quenching in oxygen atmosphere at To = 900°C were found to contain an orthorhomblc phase with T, = 8 7 K
L A T E S T research findings show that in the Y - B a C u - O system samples with an orthorhomblc phase and a composition close to Y~Ba2Cu307 have the highest critical temperature (To = 90-94 K) [1-8] The formation of a superconducting phase with an optimal composition and a mlcrostructure both in monocrystals and in ceramic samples is a complex process This process depends on the phase transformations of the system and on the state of the oxygen in the system, which is closely related to the transformations on the concentration of oxygen and the location of the oxygen atoms in the crystal lattice Despite the numerous experimental data that have appeared of late, the said problem has not so far been fully elucidated This lack of knowledge is due to a strong dependence of the obtained results on concrete experimental conditions [1-8] The purpose of our work is to investigate under controlled and reproducible conditions the superconducting properties and the structure of phases formed in quenched YIBa2Cu3Ov ~ ceramic samples We assume that the method of sudden quenching makes it possible to combine in the same samples the condltlOnS of thermal treatment, structure and lowtemperature electrophysical measurements Experiments were carried out with slntered ceramic samples 2 m m in diameter and 4 m m in height The starting samples had the following properties Their composition, as determined with the aid of the X-ray mlcroanalyzer JXA-5, corresponded within + 2 - 3 % to the composition of YiBa2Cu3OT_~ The samples within the said limits had a uniform composition and were free of Inclusions of other phases The X-ray data obtained with the aid of the D R O N diffractometer indicate that the starting samples cor713
respond to an orthorhomblc phase having the following parameters a = 3 826 + 0002/k, b -3 889 + 0 0 0 2 A , c = l l 667 + 0 006A On the basis of magnetic susceptibility, (alternating current at a frequency of l l l H z (Xa¢)), It was found that T, = 90K, with a 2 K transition width, ATc, which was determined as a 90% j u m p in the susceptibility for all the samples The amount of the superconducting phase, measured with the aid of the S Q U I D magnetometer and determined as the ratio between the forced-out flux (the Melssner effect) and the diamagnetic shielding, was found to be 45-50% (in a 0 01 Gauss field) The following procedure was used for the thermal treatment of the sample and subsequent measurements The above-analyzed samples were heated in the atmosphere of pure dry oxygen (Po, = 1 atm) at a rate of 10-15°C mln -~ up to the quenching temperature, TQ, which was varied in the range from 100 to 1000°C When this temperature was reached the sample was kept at a certain TQ and Po; = 1 atm for a period z = 3h, for quenching temperature TQ = 1000°C the period z = 30mln Following this, the samples, while remaining in oxygen atmosphere, were subjected to quenching at a rate Vo ,-- 100°C sec -~ The quenched samples were kept in liquid nitrogen without contact with air Electrophysical and X-ray analyses were carried out without the warming up of samples above 120 K For all the samples the values of T,, based on Xac measurements, as the function of the quenching temperature, To, are shown in Fig 1 It can be seen that the critical temperature of the superconducting transition is a non-monotonous function of To In the 20-500°C range the critical temperature T, = 90 K, as
Q U E N C H E D YI Ba2Cu3OT-x C E R A M I C PHASES
714
Vol 67, No 7
0I
/,o
"'ItI] o
5'00
lice • • eeOee •
'g
0,5
I000 •
Fig 1 The critical temperature of superconducting transition, T,, as the function of the quenching temperature, To, for ceramic samples, YI Ba2CujO7-x • the center of the superconducting transition, I - - 90% changes in Zac (T), ~ - - rate of quenching ~- 100°C s -~, ~ - - rate of quenching ~-500°C s -l -
• •
el
-
one approaches To = 500°C the superconducting transition has an insignificant enlargement up to T, _ 7 K In this range there was an orthorhomblc phase with parameters that were identical to those in the onginal sample When quenching was carried out at 600°C ~< To ~< 800°C the critical temperature first decreased, reaching a mimmum T, = min = 62 K at Ta = 700°C, and then again increased The transition width m this ease increased up to AT~ - 30K Data on the structure indicate the presence of an orthorhomblc phase having the following parameters (for To = 700°C) a = 3822 + 0 0 0 2 A , b = 3882 + 0 002 A, c = 11 647 + 0 00-6A, i e close to those of the starting samples With a 5-fold increase in the rate of quenching the Xac (T) curve had two sections with 7", = 60 K and T, ~ 80 K, indicating a possible twophase composition of the samples These results accord with published data [1, 3, 4], where in the Y~ Ba2Cu307 x system an orthorhombic phase was present both, at T, = 9 0 K and T, = 60K With an increase m the quenching temperature up to To -- 900°C, the crmcai temperature was restored up to T, = 85 K An X-ray analys~s of the sample in th~s case showed the presence of an orthorhomblc phase having the following parameters a = 3 820 + 0 0 0 2 A , b = 3888 _+ 0 0 0 2 A , c -- 11665 4- 0006 ,~, which are close to the lmtlal parameters When the rate of coohng was increased five t~mes, there was a sudden narrowing of the transmon w~dth to AT, = 7 K, whde the crmcal temperature increases to 87 K without there being any structural changes in the sample The results of the measurements of X~c(T) and R(T) for a sample subjected to quenching from To = 900°C are shown m Fig 2 The dependence of the R(T) corresponds to the metallic type the values o f R m the 250-100 K range underwent approximately a 2-fold decrease, the onset of superconducting tran-
-I0 0
so
I
,oo
,;o
2;o
r,K °
Fig 2 The relationship of ;(a c (T) and R(T)/R(250 K) for Y~ Ba2Cu307_ x subjected to a quenching at temperatures starting at To = 900°C Sltlon corresponds to 95 K, the electrical resistance becomes zero at 91 K A further increase m To results m a sharp decrease m 7", and a significant enlargement of the transition width, however, superconductivity is retained up to Te = 1000°C, the structure corresponds as before to the orthorhomblc phase, and there are no changes in the b and c parameters, while parameter a slightly increases reaching 3 829 A (for To = 1000°C) Thus, we have established the existence of an orthorhomblc superconducting phase in samples which have been subjected to quenching in the atmosphere of oxygen at temperatures from 100 to 1000°C At quenching temperature of 900°C there was a narrow superconducting transition at T, = 87 K These results significantly differ from published data [1, 4] obtained from a study of the R ( T ) dependence for Y~ Ba2CujO7 x ceramm samples which were quenched m air For these samples at To i> 700°C there was a sharp decrease in T, or the absence of superconducting transition, and the semlconducting nature of the R ( T ) dependence and the presence of a tetragonal phase m the samples were observed We beheve that the observed differences are due to the specific nature of quenching in the atmosphere of oxygen The results of such quenching is the formation of phases that reflect the ordering of oxygen atoms in the crystal lattice REFERENCES 1 2 3
K Klshlo, J Shlmoyama, T Hasegawa, K Kltarawa & K Fuckl Jap J Appl Phys 26, L1228 (1987) A Manthlram, J S Swlnnea, Z T Sul, H Stemfink & J B Goodenough J Am Chem Soc 109, 6667 0987) H Oyanagl, H Ihara, T Matsubara, M Tokumoto, T Matsush~ta, M Hlrabayashl, K
Vol 67, No 7
4
5 6
QUENCHED Yi Ba2Cu307-x CERAMIC PHASES
Murata, N Terada, T Yao, H Iwasakl & Y Klmura Jap J Appl Phys 26, L1561 (1987) YuMel, C Jlang, S M Green, H L L u o & C Polms Z Phys B 69, 11 (1987) S Leng, N Narlta, K Hlgashzda & H Mazakl Jap J Appl Phys 26, L1394 (1987) J D Jorgensen, M A Beuo, D G Hlnks, L Soderholm, K J Vohn, R L Hltterman, J D
715
Grace, Ivan K Schuller, C U Serge, K Zhang & M S Kleefisch Phys Rev B 36, 3608 (1987) S Lm, X Zhang, X Jlang, H Q1, N Zhu, Z Yang, X Zeng, Y Duan & G Qmo J Phys C 20, L539 (1987) Y Nakarawa, M Ishlkawa, T Takabatake, K Koga & K Terakura Jap J Appl Phys 26, L796 (1987)
0038-1098/88 $3 O0 + O0 Pergamon Press plc
S U P E R C O N D U C T I V I T Y O F Q U E N C H E D Yl Ba2Cu307-x C E R A M I C PHASES V F Degtyareva, O V Zharikov, B G Karepov, A M Kokotln, D N Mogllyansky, R K Nlkolaev, N S Sldorov and V Sh Shekhtman Institute of Solid State Physics, Ac Scl USSR Chernogolovka Moscow obl 142432, USSR
(Received 8 Aprd 1988 by V M Agranovwh) An investigation has been carrrled out of how heating in oxygen atmosphere followed by quenching affects the structure and superconducting properties Y~BaECUjO7_, ceramic samples It is shown that the critical temperature of the superconducting transition, Tc, is a non-monotonous function of the quenching temperature, T o Samples subjected to an abrupt quenching in oxygen atmosphere at To = 900°C were found to contain an orthorhomblc phase with T, = 8 7 K
L A T E S T research findings show that in the Y - B a C u - O system samples with an orthorhomblc phase and a composition close to Y~Ba2Cu307 have the highest critical temperature (To = 90-94 K) [1-8] The formation of a superconducting phase with an optimal composition and a mlcrostructure both in monocrystals and in ceramic samples is a complex process This process depends on the phase transformations of the system and on the state of the oxygen in the system, which is closely related to the transformations on the concentration of oxygen and the location of the oxygen atoms in the crystal lattice Despite the numerous experimental data that have appeared of late, the said problem has not so far been fully elucidated This lack of knowledge is due to a strong dependence of the obtained results on concrete experimental conditions [1-8] The purpose of our work is to investigate under controlled and reproducible conditions the superconducting properties and the structure of phases formed in quenched YIBa2Cu3Ov ~ ceramic samples We assume that the method of sudden quenching makes it possible to combine in the same samples the condltlOnS of thermal treatment, structure and lowtemperature electrophysical measurements Experiments were carried out with slntered ceramic samples 2 m m in diameter and 4 m m in height The starting samples had the following properties Their composition, as determined with the aid of the X-ray mlcroanalyzer JXA-5, corresponded within + 2 - 3 % to the composition of YiBa2Cu3OT_~ The samples within the said limits had a uniform composition and were free of Inclusions of other phases The X-ray data obtained with the aid of the D R O N diffractometer indicate that the starting samples cor713
respond to an orthorhomblc phase having the following parameters a = 3 826 + 0002/k, b -3 889 + 0 0 0 2 A , c = l l 667 + 0 006A On the basis of magnetic susceptibility, (alternating current at a frequency of l l l H z (Xa¢)), It was found that T, = 90K, with a 2 K transition width, ATc, which was determined as a 90% j u m p in the susceptibility for all the samples The amount of the superconducting phase, measured with the aid of the S Q U I D magnetometer and determined as the ratio between the forced-out flux (the Melssner effect) and the diamagnetic shielding, was found to be 45-50% (in a 0 01 Gauss field) The following procedure was used for the thermal treatment of the sample and subsequent measurements The above-analyzed samples were heated in the atmosphere of pure dry oxygen (Po, = 1 atm) at a rate of 10-15°C mln -~ up to the quenching temperature, TQ, which was varied in the range from 100 to 1000°C When this temperature was reached the sample was kept at a certain TQ and Po; = 1 atm for a period z = 3h, for quenching temperature TQ = 1000°C the period z = 30mln Following this, the samples, while remaining in oxygen atmosphere, were subjected to quenching at a rate Vo ,-- 100°C sec -~ The quenched samples were kept in liquid nitrogen without contact with air Electrophysical and X-ray analyses were carried out without the warming up of samples above 120 K For all the samples the values of T,, based on Xac measurements, as the function of the quenching temperature, To, are shown in Fig 1 It can be seen that the critical temperature of the superconducting transition is a non-monotonous function of To In the 20-500°C range the critical temperature T, = 90 K, as
Q U E N C H E D YI Ba2Cu3OT-x C E R A M I C PHASES
714
Vol 67, No 7
0I
/,o
"'ItI] o
5'00
lice • • eeOee •
'g
0,5
I000 •
Fig 1 The critical temperature of superconducting transition, T,, as the function of the quenching temperature, To, for ceramic samples, YI Ba2CujO7-x • the center of the superconducting transition, I - - 90% changes in Zac (T), ~ - - rate of quenching ~- 100°C s -~, ~ - - rate of quenching ~-500°C s -l -
• •
el
-
one approaches To = 500°C the superconducting transition has an insignificant enlargement up to T, _ 7 K In this range there was an orthorhomblc phase with parameters that were identical to those in the onginal sample When quenching was carried out at 600°C ~< To ~< 800°C the critical temperature first decreased, reaching a mimmum T, = min = 62 K at Ta = 700°C, and then again increased The transition width m this ease increased up to AT~ - 30K Data on the structure indicate the presence of an orthorhomblc phase having the following parameters (for To = 700°C) a = 3822 + 0 0 0 2 A , b = 3882 + 0 002 A, c = 11 647 + 0 00-6A, i e close to those of the starting samples With a 5-fold increase in the rate of quenching the Xac (T) curve had two sections with 7", = 60 K and T, ~ 80 K, indicating a possible twophase composition of the samples These results accord with published data [1, 3, 4], where in the Y~ Ba2Cu307 x system an orthorhombic phase was present both, at T, = 9 0 K and T, = 60K With an increase m the quenching temperature up to To -- 900°C, the crmcai temperature was restored up to T, = 85 K An X-ray analys~s of the sample in th~s case showed the presence of an orthorhomblc phase having the following parameters a = 3 820 + 0 0 0 2 A , b = 3888 _+ 0 0 0 2 A , c -- 11665 4- 0006 ,~, which are close to the lmtlal parameters When the rate of coohng was increased five t~mes, there was a sudden narrowing of the transmon w~dth to AT, = 7 K, whde the crmcal temperature increases to 87 K without there being any structural changes in the sample The results of the measurements of X~c(T) and R(T) for a sample subjected to quenching from To = 900°C are shown m Fig 2 The dependence of the R(T) corresponds to the metallic type the values o f R m the 250-100 K range underwent approximately a 2-fold decrease, the onset of superconducting tran-
-I0 0
so
I
,oo
,;o
2;o
r,K °
Fig 2 The relationship of ;(a c (T) and R(T)/R(250 K) for Y~ Ba2Cu307_ x subjected to a quenching at temperatures starting at To = 900°C Sltlon corresponds to 95 K, the electrical resistance becomes zero at 91 K A further increase m To results m a sharp decrease m 7", and a significant enlargement of the transition width, however, superconductivity is retained up to Te = 1000°C, the structure corresponds as before to the orthorhomblc phase, and there are no changes in the b and c parameters, while parameter a slightly increases reaching 3 829 A (for To = 1000°C) Thus, we have established the existence of an orthorhomblc superconducting phase in samples which have been subjected to quenching in the atmosphere of oxygen at temperatures from 100 to 1000°C At quenching temperature of 900°C there was a narrow superconducting transition at T, = 87 K These results significantly differ from published data [1, 4] obtained from a study of the R ( T ) dependence for Y~ Ba2CujO7 x ceramm samples which were quenched m air For these samples at To i> 700°C there was a sharp decrease in T, or the absence of superconducting transition, and the semlconducting nature of the R ( T ) dependence and the presence of a tetragonal phase m the samples were observed We beheve that the observed differences are due to the specific nature of quenching in the atmosphere of oxygen The results of such quenching is the formation of phases that reflect the ordering of oxygen atoms in the crystal lattice REFERENCES 1 2 3
K Klshlo, J Shlmoyama, T Hasegawa, K Kltarawa & K Fuckl Jap J Appl Phys 26, L1228 (1987) A Manthlram, J S Swlnnea, Z T Sul, H Stemfink & J B Goodenough J Am Chem Soc 109, 6667 0987) H Oyanagl, H Ihara, T Matsubara, M Tokumoto, T Matsush~ta, M Hlrabayashl, K
Vol 67, No 7
4
5 6
QUENCHED Yi Ba2Cu307-x CERAMIC PHASES
Murata, N Terada, T Yao, H Iwasakl & Y Klmura Jap J Appl Phys 26, L1561 (1987) YuMel, C Jlang, S M Green, H L L u o & C Polms Z Phys B 69, 11 (1987) S Leng, N Narlta, K Hlgashzda & H Mazakl Jap J Appl Phys 26, L1394 (1987) J D Jorgensen, M A Beuo, D G Hlnks, L Soderholm, K J Vohn, R L Hltterman, J D
715
Grace, Ivan K Schuller, C U Serge, K Zhang & M S Kleefisch Phys Rev B 36, 3608 (1987) S Lm, X Zhang, X Jlang, H Q1, N Zhu, Z Yang, X Zeng, Y Duan & G Qmo J Phys C 20, L539 (1987) Y Nakarawa, M Ishlkawa, T Takabatake, K Koga & K Terakura Jap J Appl Phys 26, L796 (1987)