PenanikaJ. Sci. & Techno!. 3(1):179-186(1995)ISS, : 0128-7680

© Universiti Penanian Malaysia Press

COMMUNICATION I

Onset of Orthorhombic-tetragonal Structure in(YBa2Cu307_sh_x(Sn02)x Superconducting Ceramics

Received 27 February 1993

ABSTRAKSuperkonduktor suhu tinggi, (YBa~Cu~07.8)l_x(SnO~)x dengan x berubah dari0.00 hingga 0.06 telah disediakan dalam udara di bawah keadaan pensinteranyang optimum. Kesuperkekonduksian dan titik mula peralihan strukturortorombik - tetragonal dibincangkan berdasarkan kepada hasil kajian belauansinar-X. Kesan Meissner pada suhu melebihi suhu cecair nin-ogen dicerapuntuk semua sampel dan ini menunjukkan pengekalan struktur ortorombik didalam sistem berlaku sehingga penggantian Sn sebanyak 6%.

ABSTRACTHigh Tc superconductors, (YBa2Cu~07-8)l_x(SnO~)x with x ranging from 0.00 to0.06 were prepared in air under optimum sintering conditions.Superconductivity and the onset of orthorhombic-tetragonal structure are dis­cussed in relation to the results of X-ray diffraction studies. Meissner effectabove liquid nitrogen temperature was observed for all the samples, suggestingthe retention of orthorhombic structure in the system up to 6% Sn substitution.

INTRODUCTION

Following the discovery of superconductivity in the Y-Ba-Cu-O system (Wu etai. 1987), numerous researchers began to explore the feasibility of substi­tuting different elements into the YBa~CU~07-li structure. To date, somedegree oflattice substitution has been achieved on each site in the structure.Part of the initial enthusiasm for substitutions came from the possibility offurther raising the superconducting transition temperature (Murphy et ai.1987: Nishi et ai. 1988). More recent studies have focused on the structural,valence and magnetic effects of cation substitution in an effort to understandthe relevance of various structural features to superconductivity. .Severalclear issues have emerged from these studies, of which the most important isthe unique square planer Cu-atoms each surrounded by 4 or 6 oxygen atomsand crucial to the superconductivity observed in oxides (Izumi et al. 1987).The aim of this work is to focus on the effect of interstitial substitution of Snin the (YBa~Cu~07_8)l_x(Sn02)x system for x = 0.00 to 0.06. There are not manypapers reporting on the effect of Sn substitution on the materials (Suzuki etai. 1988; Paulose et ai. 1991) compared to other dopants (Suzuki et ai. 1988;Mikhailov et al. 1990).

A. Halim Shaari, Mansor Hashim, Sidek Hj. Ab. Aziz,jamil Suradi and Naemah i\lohd. Shafie

MATERIALS AND EXPERIMENTAL METHODS

In this work, (YBa2Cu307_&) l_x(Sn02)x compounds were prepared by the solid­state reaction method using an appropriate mixture of 99.99% pure Y20:1,BaC03, CuO and Sn02. After 12 hours of mixing and grinding, the samples werecalcined at 850°C for 24 hrs in air. The samples were ground, sieved to obtainparticles of -640 mm in size and cold-pressed into a disc-shaped pellet ofabout 6 mm diameter and 1-2 mm thickness by applying a pressure of about140 kN/cm2. Finally, the samples were sintered in air under optimumconditions (Shaari et al. 1991) at 950°C for 24 hours.

The morphology of the materials thus prepared was observed by a scanningelectron microscope modeIJoelJSM-35C. X-ray powder diffraction was doneusing Philips diffractometer PW 1730 and lattice constants ofthe compoundswere determined. The Meissner effect, used as a litmus test for supercon­ductivity, was observed by levitating a small strong permanent magnet, d­Fe-B, over liquid nitrogen-cooled samples.

Resistivity measurements on pure YBa2Cu307-S were carried out by a standardd.c. four-probe method with a current of 1 rnA. The superconducting transi­tjon temperature of a 5% Sn sample was also measured in terms of com­plex susceptibility, % = X - ix, using a Lakeshore a.c. susceptometer model7000. Results of measuremen ts for other samples will be reported in detail else­where.

RESULTS AND DISCUSSION

The X-ray powder diffraction patterns at various Sn concentrations areshown in Fig. 1. The diffraction patterns demonstrate that (YBa2Cu~07-S)I_x

(Sn02)x exists almost as single phase materials for samples at x = 0.00,0.01,0.02 and 0.03 where the characteristic peaks of orthorhombic YBa2Cu~07-S

predominate (Beyers and Shaw 1989). However for samples ofx = 0.04,0.05and 0.06, other minor phases were observed and are evident from the additionalpeaks in the diffraction patterns.

Changes in the lattice constants of YBa2Cu307-S against Sn concentrationsare as shown in Fig. 2. The length of the b-- and c-axes did not change drasti­cally with the increase of Sn concentrations. On the other hand, the a-axisexpanded significantly from Sn concentration ofx = 0.03 and finally becameequal to the b-axis at x - 0.06, the onset of transition from orthorhombic totetragonal structure.

The effect of interstitial or lattice substitution of Sn is also evident fromthe volume expansion as shown in Fig. 3, where abrupt change in volumeoccurs at Sn concentration of x - 0.03. As yet there is no evidence as towhether Sn goes into the system interstitially or by lattice substitution andhence the ordering of Sn atoms is not known. However, Sn atoms do effectthe system spatially.

More evidence for the onset of transition from orthorhombic to tetrago-

180 PertanikaJ. Sci. & Techno!. Vol. 3 No. I, 1995

Onset of Orthorhombic-tetragonal Structure

~

." '"'0 0

::: 2- ~~ ~ :::;0 0 :::;0 -

-;-c:

" 0.05>,..'".......,;;;

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24 28 32 36 40 44 48 52 56 60

2 - THETA

Fig 1. X-ray difJiaction pattern of (YBa2Cu307_8) l-x(Sn02,Jx ( x = 0.00 to 0.06)

nal phase is shown by the intensity peaks of the X-ray diffraction patterns at28 ~ 32-33° as shown in Fig. 4. As onset is approached, the minimum peakclose to 28 ~ 32° increases and finally almost equals the maximum peak. Inorder to observe the changing of the position of the minimum peak from28 ~ 32° to 28 ~ 33°, additional data for Sn concentration of x - 0.07 isrequired because at that concentration the system will exist completely intetragonal phase. The evidence discussed above could similarly be seenfrom X-ray diffraction patterns at 28 ~ 38° - 41° , 46° - 48° and 58° - 60°, asthese peaks represent the characteristic peaks of YBa2Cu:10n (Izumi et al.1987) .

Evidence of superconductivity in the system can be qualitatively deducedfrom the observation of shielding behaviour of the superconductors due toMeissner effect. In this work, all the samples (x =: 0.00 to 0.06) displayed thebehaviour well above liquid nitrogen temperature.

A previous finding (Beyers and Shaw 1989), suggests that T c remains at90K for oxygen concentration from 07.0 to 069' and then falls to a - 60K'plateau' between 0(j7 and 0(j6 and finally drops to zero (i.e. not supercon­ducting between 06.5 and °(4) as shown in Fig. 5. Hence it could be deduced

PertanikaJ Sci. & Technol. Vo!. 3 No.1, 1995 181

A Halim Sham'i, MansOI' Hashim, Sidek Hj. Ab. Aziz,Jamil Suracli and Naemah Mohd. Shafie

c

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x (% Sn02 )

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•176

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182 PertanikaJ. Sci. & Techno!' Va!. 3 No. I, 1995

Onset of OrthorhOinbic-tetragonal Structure

0.050.040.030.02x c 0.00 0.01

that the oxygen content of the samples prepared in this work must be - 0liH,since all samples displayed Meissner effect above 77K Paulose et. at. (1991)suggested that the rate of oxygen absorption would increase in YBa2Cu30nby Sn02 addition.

A quantitative measurement of temperature dependence of sample resis­tance has been done. Fig. 6 shows the temperature variation of resistance forpure YBa2Cu:,07_0 and T c was found to be around 90K From the qualitativemeasurements of the dependence of the component fI ' of the complex sus­ceptibility with temperature for a 5% Sn sample, as shown in Fig. 7, Tc wasfound to be about 80K More detailed results on the magnetic properties ofthe samples will be reported elsewhere.

CONCLUSION

In conclusion the substitution of Sn atoms up to 6 at% in the YBCa systemdoes not give rise to a drastic change in TO' which agrees with Suzuki et at.(1988), as compared to Zn, Fe or Co substitution (Strobed et at. 1988; Beyersand Shaw 1989; Shaari et al. 1992), where T c is su'ongly suppressed. Theretention of an orthorhombic structure with Sn atoms having little effect onTc in the (YBa2Cu307-e) l_x(Sn02)x system up to x = 0.06 could be rationalizedon the basis that Sn substitutes as +4 valence state (Zhang et al. 1989) andhence could draw excess oxygen into the structure in order to increase theiroxygen coordination.

PenanikaJ. Sci. & Techno!' Va!. 3 No.1, 1995 183

Onset of Orthorhombic-tetragonal Structure

100~..~

80 -----77K(J...60 ••••40 - •20

0

6.0 6.2 6.4 6.6 6.8 7.0

Fig. 5. Superconductivity transition temjJeratuni versus oxygencontents (BeyelS and Shaw 1989)

2.0

E 1.5.co

QJ(J 1.0"'"oJ

'"."'" 0.5QJ

'"0.0

0 50 100 150 200 250 300

Tempera ture (K)

Fig. 6.

.~ 0.8c

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'"" -0.3Ul

u-<

-0.6

Resistance versus temperature of pure YBaCuO

7\.-".................

o 20 40 60 80 100 120 140

Temperature (10

Fig. 7. Temperature variation of real Xl and imaginary Xl I componentsof susceptibility of (5 % Sn)

184 PertanikaJ. Sci. & Techno!. Vol. 3 No.1, 1995

A. Halim Shaari, MansoI' Hashim, Sielek Hj. Ab. Aziz, .ramil Snracli anel Naemah Mohel. Shafie

ACKNOWLEDGEMENTS

The authors would like to express their gratitude to the MPKS T, under pro­ject IRPA: Code 50319, for funding the project. Thanks are also due to thetechnical staff of Physics Department, UPM.

A. HALIM SHAARI, MANSOR HASHIM,SIDEK HJ. AB. AZIZ,JAl\1IL SURADI

and NAEMAH MOHD. SHAFIEDepartment ofPhysicsFaculty ofScience and Environmental StudiesUniversiti Pertanian Malaysia43400 Serdang, Selang01" Darul Ehsan, Malaysia

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STROllED, P., C. PAUl_SEN andJ.L. THOLENCE. 1988. Superconducting properties of substi­tuted YBa2Cu2(1_x)M~x07_o'Solid State Cumin. (USA) 65(7): 585-589.

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Onset of Orthorhombic-tetragonal Structure

SUZUKI, T., T. YA\'IAZAKI, A. KAUKlI.U, M. MALDA, H. SEK] and T. TAKAHASHI. 1988.Superconductivity transition temperature in the (YBa~Cu:j07"')).x (lVIeO) x system(MeO = PbO, SrO, ZnO, Bi~O:j, SnO~ , TeO, V~O:i' WO~ and MoO~) J. Mater. Sci. Lett. (UK)7(9): 926-927.

Wu, M.K.., J.P. AsHI3URi':, CJ. THONG, P.H. HOR, R.L. MENG, L. GAO, Z.L. HUANG, Y.Q.WANG and C.W. CHU. 1987. Superconductivity at 93K in a new mixed phase Y-Ba-Cuocompound system at ambient pressure. Ph),s. Rev. Lett. 58: 908-910.

ZHANG, H., G.M. WANG and Q.R. ZHANG. 1989. Mossbauer effect and structure of the

YBa2Cu3xSnx07_0' Ph)'s. Lett. A (Netherlands) 138(9): 512-522.

186 PertanikaJ. Sci. & Technol. Vol. 310. I, 1995