High Tc superconductivity in YxBa1-xCuO3-δ

High Tc superconductivity in YxBa1-xCuO3-δ

Solid State Communications, Vol. 64, No. 3, pp. 339-341, 1987. Printed in Great Britain. 0038-1098/87 $3.00 + .00 © 1987 Pergamon Journals Ltd. HIGH...

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Solid State Communications, Vol. 64, No. 3, pp. 339-341, 1987. Printed in Great Britain.

0038-1098/87 $3.00 + .00 © 1987 Pergamon Journals Ltd.

HIGH Tc SUPERCONDUCTIVITY IN YxBal_~CuO3_,~ K.H. Lii Institute of Chemistry Academia Sinica Nankang, Taipei, Taiwan, ROC M.F. Tai, H.C. Ku* Department of Physics, National Tsing Hua University, Hsingchu, Taiwan, ROC and S.L. Wang Department of Chemistry, National Tsing Hua University, Hsingchu, Taiwan, ROC

(Received 7 April 1987 by H. Suhl) We report the results of resistivity measurements in YxBat_xCuO3_, (x = 0.3, 0.4, 0.5, 0.6). The x = 0.4 sample shows a superconducting transition at 96.7 K with a width of 1.6 K. Our X-ray analysis on the X -- 0.4 sample indicates that the material exhibiting superconductivity is an orthorhombic perovskite phase with a = 3.894(1)A, b = 3.826(1)A, c = 11.682(2)A. 1. INTRODUCTION

99%). The compounds with the nominal composition THE DISCOVERY OF high temperature super- YxBal_xCuO3_6 (x = 0.3, 0.4, 0.5, 0.6) were each conductivity in the system of La-Ba(Sr)-Cu-O by prepared by heating the reaction mixture containing Bednorz and Miiller [1] has attracted much attention appropriate amounts of the starting materials in air al on these potentially useful materials. Subsequent stu- 900°C in an alumina crucible for 20 h with an interdies [2-5] showed that the K2NiF4-type phase was mediate grinding. Each product was pulverized, pressresponsible for the observed superconductivity. ed into a few pellets, sintered in air at 900°C for 15 h, Recently, Wu et al. [6] reported a remarkable material and cooled to room temperature by removing them with a nominal composition of YL2Ba0s CuO4_~ which from the furnace while at the sintering temperature. had a superconductivity transition between 80 and Portions of the sintered pellets were used for resistivity 93 K. For the first time, a zero-resistance state is measurements, and portions were resintered in flowachieved in a liquid nitrogen Dewar. However, their ing oxygen at 900-950°C, quenched to room temX-ray analysis on the sample showed the existence of perature in the oxygen flow, and characterized to multiple phases uncharacteristic of the K2NiF4-type determine the effects of the sintering atmosphere on structure. Therefore, we decided to study materials the observed resistivities. The reaction conditions for with different nominal compositions. In this report, each sample are listed in Table 1 along with the resiswe present the preparation, powder X-ray analyses, tivity measurement results. A four-probe technique and resistivity measurement results of YxBa~_x was employed in the resistivity measurements and a close cycle refrigerator was used for cooling the samCuO3_~ (x = 0.3, 0.4, 0.5, 0.6). pies. Electrical contant was made to the sample through platinum wires attached to the sample with 2. EXPERIMENTAL PROCEDURES conducting silver paint. The temperature was deterThe starting materials used for sample prepara- mined with a Si-diode temperature sensor. In the tion were Y203 (Strem Chemicals, 99.999%), barium measurements, each sample was quickly cooled down carbonate (Merck, 99%), and cupric oxide (Merck, to about 8 K and then slowly warmed up to room temperature at a rate of about 1 K min -1. Powder * Also at the Ames Laboratory-USDOE and DepartX-ray diffraction patterns at room temperature were ment of Physics, Iowa State University, Ames, IA taken with a Rigaku powder diffractometer using Cu 50011, USA. Similar work was reported at the March 1987 APS K~t radiation (2(Cu Kal ) = 1.5405 A). The computer meeting. The work described in this paper was car- program TREOR [7] was used for indexing the powried out independently. der diffraction patterns. 339

340

Vol. 64, No. 3

H I G H T c S U P E R C O N D U C T I V I T Y IN YxBal_~CuO3_, t.0

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Table 2. X-ray powder "Y0.4 Bao.6CuO3- ~"

diffraction pattern for

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2r ........

d (obs)

d (calc)

(A)

(h)

relative intensity

hk 1

2.5 9.8 4.1 3.8 4.6 52.0 100.0 2.3 3.9 10.2 9.0 16.8 18.0 10.2 23.0 11.5

002 003 0 10 10 2 0 12 10 3 0 13 111 1 12 005 0 14 1 13 006 020 1 16 12 3

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5.859 3.897 z o.¢ J o.5 1"° 1 " . 3.836 o ,, \ 3.236 o,o " 3.205 o.l~ 74 8Z 90 9e toe o T( K ) 2.750 Ii ~=÷a.~¢?: 0 ¢0 e0 120 lao 20o 2¢0 z80 2.728 T ( K ) 2.658 2.472 Fig. 1. Normalized resistivity of"Y0.4 Ba0.6CuO3-6" as a function of temperature. The open rhomboid is for 2.337 the sample annealed in air, while the solid rhomboid 2.324 is for the sample annealed in oxygen. Inset: expanded 2.235 view of the resistivity transition for the same two 1.946 samples. 1.912 1.585 1.571 3. R E S U L T S A N D DISCUSSION 0.5

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Figure 1 shows plots of normalized resistivity vs temperature for "Y0.4 Bao.6CuO3-,~".The sample which was sintered in air, represented by open rhomboid, had Toner = 93 K and became fully superconducting at 83 K. Interestingly, the resistivity o f the sample above Tnn~t was essentially temperature-independent. Further sintering in an oxygen atmosphere raised the onset temperature from 91 to 96.7 K and narrowed the transition width down to 1.6 K. Similar improvements in the observed properties by sintering in 02 were also found in the x = 0.3 and x = 0.5 samples. In contrast to the x = 0.34).5 samples, the x = 0.6 sample

Table 1. Chemical compositions, firing conditions, and resistivity measurement results for YxBal_x CuOs_a x

firing

Tonse t

Tcl a

T_cob

AT c

(K)

(K)

(K)

(K)

air 02 air 02 air 02 air

85.1 110 93.0 96.7 94.5 110 . .

79.8 91.5 91.0 95.7 89.0 92.0 . .

71.0 87.5 83.0 94.0 81.0 88.0

8.7 2.6 7.0 1.6 8.5 4.5

02

.

.

conditions

(°C) 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6

900. 900. 900. 950. 900. 900. 900. 900.

.

.

a The midpoint of superconductivity transition. b Zero-resistance temperature. ¢ Width between 10 and 90% superconductivity transition.

5.8410 3.8940 3.8260 3.2400 3.2005 2.7535 2.7291 2.6576 2.4725 2.3364 2.3215 2.2349 1.9470 1.9130 1.5850 1.5710

did not become superconducting, although a significant drop in resistance at about 80 K was observed. A study of the X-ray powder patterns of "Y0.4Bao.6CuO3_~", which was sintered at 900°C in air, and "Yt.2Ba0.sCuO4_~", which was prepared according to Wu et al. [6], indicates that "YL2Ba0.8 CuO4_~" does not contain any material with the K2NiF4-type structure and its diffraction peaks can be classified into two groups (A & B). Based on the relative intensities, group A represents the major phase(s) in "Y~2Ba0.sCuO4_~", while group B becomes dominant in "Y0.4Ba0.6CuOa_,~''. After subtracting the group A reflections from those of "Y0.4Bao.6CuO3_,~", one obtains a pattern which is similar to that for LaNiO3 [8], suggesting a perovskite phase as the dominant component in the x = 0.4 sample. By using the computer program T R E O R , the pattern can be completely indexed on the basis of an orthorhombic unit cell with a = 3.894(1)A, b = 3.826(1)A, c = 11.682(2)A. The indexing results are given in Table 2. The unit cell parameters indicate that the material has a distorted perovskite structure and its cell volume is three times the ideal cubic perovskite structure. Interestingly, the X-ray pattern for the x = 0.4 samples, which was resintered in an oxygen atmosphere at 950°C, showed a marked change in the relative intensities. The change could be due to different orderings of the Ba and Y atoms in the perovskite structure. Detailed analysis of the intensity data are under way.

Vol. 64, No. 3

H I G H Tc SUPERCONDUCTIVITY IN YxBal_xCuO3_~

Acknowledgements - - The authors wish to thank the National Science Council of the Republic of China for financial support of this study under the contract No. NSC76-0208-M007-15 and NSC76-0208-M007-79. K. H. Lii would also like to thank the support from Institute of Chemistry Academia Sinica.

3. 4. 5. 6.

REFERENCES 1. 2.

J.G. Bednorz & K.A. Muller, Z. Phys. B64, 189 (1986). J.G. Bednorz, M. Takashige & K.A. Miiller, Europhys. Lett., in press.

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