Pertanika J. Sci. & Technol. 4(2): 231-237 (1996)ISSN,OI28·7680

© Penerbit Universiti Pertanian Malaysia

Data Acquisition System for Resistance Measurementof High-temperature Superconductors

Ahtnad Kamal Yahya, R. Abd.Shukor l and Faizah Md. Salleh

School of Applied SciencesInstitut Teknologi Mara

40450 Shah A/am, Selangor Darn/.Ehsan, MalaysUJ

JDepartment of PhysUsUniversiti Kebangsaan Malaysia

43600 Bangi, Selangor Darul Ehsan, Malaysia

Received 29 Sep[ember 1995

ABSTRAK

Kertas kerja ini membincangkan reka bentuk sistern perolehan data yangmenggunakan mikrokomputer 80486 sebagai pengawal dan dihubungkanmelalui kad PC-Lab 848B kepada multimeter berdigit dan pengawal suhumenggunakari laluan IEEE 488. Sistem ini berupaya mencatat,menyimpan dan memplat graf bagi bacaan-hacaan suhu me1awanrintangan. Pengukuran rintangan bagi fasa YBa2CuS07.S dilaporkandan dibandingkan dengan keputusan yang terdahulu. Pengukuran bagi(Yo.5Euo.5)Ba2CuS07-6 rnenunjukkan peningkatan nilai T c mula dan Tc sifar

dan ini diterangkan sebagai akibat dari perubahan tekanan dalaman didalam satah CuO yang berlaku a~abila Eu3+ yang lebih besarmenggantikari. sebahagian daripada Y +. Sistern perolehan ini mudahdigunakan dan sangat se~sitif untuk mengesan perubahan suhu gentingyang kecil. Suhu boleh diukur dengan kepersisan 0.1 K dan ketepatan ± IK yang merupakan had pengesan suhu perintang platinum ..yang

.. digunakan. Nilai imbangan sifar-mutl"ak adalah kurang daripada 0.1 K.

ABSTRACT

This paper discusses the design of a data acquisition system based on the80486 microcomputer serving as a controller connected via a PC-Lab848B card to digital multimeters and a temperature controller using IEEE488 standard bus. The system is able to log, store and plot temperatureversus resistance readings. Resistance measurement on YBa2Cu3074l) phaseis reported and compared with previous results. Measurements on (YO.5EUO.5)Ba2CuS07.S showed an increase in Tc onset and T c zero; this wasexplained in terms of change in the internal pressure in the CuO planesdue to partial substitution of larger Eu3+ in place of y3+. This dataacquisition system is simple to use and very sensitive in detecting smallvariations in transition temperatures. The temperature can be measuredwith a precision of 0.1 K and accuracy of ± I K, which is the limit of theplatinum resistor temperature sensor. The absolute-zero offset value is lessthan 0.1 K.

Ahmad Kamal Yabya, R. Abd-Sbukor and Faizab Md. Salleb

Keywords: resistance, automated data acquisition, YBa2Cu307_li supercon.ductor

INTRODUCTIONThe electrical resistivity of many metals and alloys drops suddenly to zerowhen the specimen is cooled to a sufficiently low temperature, often atemperature in the liquid helium range. At the transition temperature, T c

the specimen undergoes a phase transition from a state of normal resistiviryto a superconducting state. In the superconducting state, the dc resistivity iszero and thus current can flow in a superconductor without any loss.

The copper oxide-based superconductor was first discovered in theLaBaCuO system (Bednorz and Muller 1986). A significant leap occurredwith the discovery of the ceramic superconductor YBa2Cu30,.o (" 123")with a transition temperature higher than 90 K (Wu et al. 1987). Thediscovery led to a switch in cryogen to liquid nitrogen, which is relativelycheaper than liquid helium. The discovery of "123" has triggered the racefor other high-temperature superconductors (HTSC) and has led to thediscovery of the bismuth (Maeda 1988), thallium (Sheng and Hermann1988), mercury (Putilin et al. 1993) and calcium-doped mercury (Schillinget al. 1993) systems of high temperature superconductor. The calcium­doped mercury (Hg-Ba-Ca-Cu-O) superconductor currently has the highesttransition temperature of l34 K.

One of the important parameters of a superconductor is the transitiontemperature. This paper describes a simple, accurate method (accuracy of± I K) of determining the transition temperature of HTSC ceramics usingthe four point-probe resistance measurement. The 80486 microcomputerwas used as a controller, connected via a PC-Lab 848B card to two digitalmultimeters and a temperature controller using the IEEE 488 standard bus.The ha~dw.a"" interfacing and software development for raw data capture,storage and data conversion are discussed. Resistance measurement onYBaiCu30,_O is reported and compared with results of other researchers. Inaddition, measurements of (Yo.5Euo.5)Ba2Cu30,_o have also been made andthe results discussed.

MATERIALS AND METHODS

Sample PreparationThe YBa2Cu30,_o and (Yo.5Euo.5)Ba2Cu30,_o samples were prepared bythe standard solid state reaction method using mixed powder of Y20"EU20" BaC03 and CuO with a purity of 99.99%. The starting materialswere carefully mixed and ground in a mortar. The powders were calcined inair at 950°C for 48 h with· several intermittent grindings, and furnacecooled. The powders were then reground and pressed into l3-mm diameter,4-mm thick pellets under a· pressure of 5 tons using a hand-held hydraulic

232 Pertanika J. Sci. & Techno!. Vo!' 4 No.2, 1996

Data Acquisition System for Resistance Measurement of High-temperature Superconductors

press. These pellets were sintered in air for another 24 h at 950°C followedby a slow furnace cooling at a controlled rate of 40°C/hour to roomtemperature. A detailed preparation method has been described elsewhere(Abd-Shukor 1993). The Siemens D 5000 X-ray diffractometer was used toconfirm the resultant phase of the samples.

InstrumentationResistance measurement was done using the four-point probe technique.The distance between the current leads was 10 mm, while the distancebetween voltage leads was 5 mm. The electrical contacts to the specimenwere achieved by using silver conductive paint.

A stable de current source LakeShore Model 120 CS was used to supplya current of 50 rnA through the specimen. Higher currents were not useddue to the existence of a critical current value above which super­conductivity disappears. Typical critical current density for polycrystallinesamples is 10' - 10' A/cm2 at 77 K and zero field (Murakami 1992). Thevoltage across the specimen was measured by Keithley model 197 (5 1/2digit) Digital Multimeter (DMM) with built-in IEEE-488 Interface. Atypical value of voltage across the specimen at room temperature withconstant current set to 50 rnA was approximately 300 JlV.

The cryogenic system used wa,s aJanis VPF-100 liquid nitrogen pourfillcryostat with the necessary vacuum pump attached. The sample was placed

-in vacuum.and held relatively close to a platinum resistor temperaturesensor. A heater located at the cryostat cold head was used to control thesample temperature.

The instruments mentioned above were interfaced to a 80486microcomputer via PC-Lab 848B card to the digital multimeters usingthe IEEE 488 standard bus. The 80486 microcomputer acts as a controller

- for both DMM and temperature controller. Each device was given adifferent.. addressand sent specific talk or listen c<lmmands through the bus.The connection layout of the data acquisition system is shown in Fig. I.

Programming was done on Turbo Pascal to allow the controller tocommunicate through the lEEE-488 bus. The PC-Lab 848B Interfacecard was a convenient choice as it has ready-made software driverspackaged in read-only-memory onboard. This makes the softwareprogramming convenient and flexible. Through the software, the systemis able to log, store and plot temperature and resistance readings (Fig. 2).Each set of readings was recorded only when either a significant change intemperature or a change in voltage reading of 1 JlV in the sample wasdetected. The resolution of the temperature measurement is better than 0.1K. The software also automatically indicates the value of the transitiontemperature T c zero after each thermal scan. Tc onset was obtained bymanually moving a vertical search line on the onset location. The

Pertanika J. Sci. & Techno\. Vol. 4 No.2, 1996 2ll

Ahmad Kamal Yabya, R. Abd-Shukor and Faizab Md. Salleh

CUl'R'nt Sowee

VoltmeterDMMI

OhmmeterDMMM2

TemperatureController

System Controller I

Som ,Sam Ie Holder

Temperature: Sensor I

Cold Head

1- Heater

Tempc"'lure Sensor 2

Fig. J. Sdltmatic layout oj the data acquisition system

234

1. Usc Previous Data2. Acquire New DataJ. Run Windows4. Run DOS5. Quit

Sub Menu

I. Display Data2. Display GraphJ. Display Multi,raph4. Print Output5. Export File

Fig. 2. .Flowchart oj the data acquisition program

Pertanika J. Sci. & Technol. Vol. 4 No.2. 1996

Data Acquisition System for Resistance Measurement of High-temperature Superconductors

temperature coordinate of the search line reported by the software gives thevalue of Tc onset·

RESULTS AND DISCUSSIONThe X-ray diffraction pattern confirms the formation of the "123"perovskite-like structure of the space group P4fmmm with the generalformula YBa2CU307-8' The normalized resistance versus temperature curveshows a metallic normal-state behaviour with T c o",ct of96 K and T c zc,o of91 K (Fig. 3). We found the measurements ofYBa2Cu307_s comparable to

earlier reports (see, e.g., Kirkup 1988). A similar X-ray diffraction patternwas also obtained for the (Yo.5Euo.5)Ba2Cu307_s sample. The T c omct andT c ZCtO values of 98 K and 93 K, respectively, are slightly higher than the"123" sample (Fig. 3). This may be due to the changes in the latticeparameter as a result of substitution of the larger Eu3+ (0.95 A) in place ofy 3+ (0.89 A). This substitution could have changed the internal pressure inthe crystal structure and affect the dynamics of the charge carriers in thematerial. This result is consistent with results reported by previous workers(Guillaume 1994; Ata-Allah 1994) where T c was found to scale linearlywith the ionic radius of rare earth elements used to fully substitute y3+ inthe "123" structure.

+ (~,EuJB4CO • YBCO1.2

t0.8 t

;Z

\g 0.6e'" 0.4i<

t0.2

t0

50 100 150 200 250 300

Temperature (K)

Fig. 3. Normalized resistance of rBa~U307-f, and (rOsEuo.5)Ba~U307-f, as afwu;tumtemperature

Tests on the data acqulSltlOn system above prove it to be a reliablesystem for resistance measurements at temperatures above 77 K. Minutevariations in the microstructure of the material which can lead to changes inthe T c profile (± I K), such as in the case of the (Yo.5Euo.5)Ba2Cu307.s, can

Pertanika 1. Sci. & Technol. Vol. 4 No.2, 1996 235

Ahmad Kamal Yahya, R. Abd·Sbukor and Faizah Md. Salleh

be readily detected with our system. The full flexibility offered when using amicrocomputer and the appropriate IEEE-488 interface card has been themajor factor in the development. The system can also be improved by usinga programmable current source with built-in IEEE-488 interface. Thisallows the system to automatically reverse current direction or vary currentmagnitude during a thermal scan for more accurate resistance and Tomeasurements. Further, the sensitivity of the system may be upgraded byusing a nanovoltmeter in place of the 5 1/2 digit digital multirneter forvoltage readings. The accuracy of the temperature measurements can beimproved by using more accurate temperature sensors such as a silicondiode. Construction of a system to measure multiple samples in a singlethermal scan is in progress.

ACKNOWLEDGEMENTSResearch at ITM and UKM was supported by Bureau of Research andConsultancy (BRC) and Malaysia Toray Science Foundation, respectively.

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YBa,(Cu,.,Cr,hO,-s (x = 0 - 0.1). App. Phys. CQmm. 12(3&4): 323-331.

ATA-ALLAH, S. S., YUNHUI XU and Ch. HEIDEN. 1994. Effect of Zn doping on thesuperconductivity of RBa2Cu3.xZnx07_o (R = Vb, Er, Y, Dy, Gd, Eu, Sm andNd). Physica C 221: 39-45.

BEDNORZ, J.G. and K.A. MOLLER. 1986. Possible high T c superconductivity in theBa-La-Cu-O system. .(. Phys. B 64: 189-192.

GUILLAUME, M., P. ALLENSPACH, W. HENGGELERT, J. MESOT, B. ROESSLI, U.STAUB, P. FISHER, A. FURRER and V. TRAUNOV. 1994. Systematic lowtemperature neutron diffraction studies on RBa2CU30x. (R = yttrium and rare­earth: x ~ 6 and 7). J. CQndens. Matter 6: 7963-7976.

KIRKUP, L. 1988. Resistance measurements as a function of temperature on high-Tc

superconductor YBa2Cu307_S. Eur. J- Physics 9: 1-4.

MAEDA, H., Y. TANAKA, NL FUKUTOMI and T. ASANO. 1988. A new high-Tc oxidesuperconductor without a rare earth element. ]pn. ]. Appl. Phy,. Lett. 27: L127­Ll30.

MURAKAMI, M. 1992. Processing of bulk YBaCuO. SupercQnd. Sci. Tech1..l.5: 185-203.

PUTILI', S.N., LV. A TIPOV, 0. CHAMAISSEM and M. MAREZIO. 1993.Superconductivity at 94 K in HgBa2Cu04+S' Nature 362: 226-228.

SCHILLING, A., M. CANTONI, J.D. GUO and H.R. OTT. 1993. Superconductivityabove 130 K in the Hg-Ba-Cu-O system. Nature 363: 56-58.

SHENG, Z.Z. and A.N!. HERMANN. 1988. Superconductivity in the rare-earth-free TI­Ba-Ca-Cu-O system above liquid-nitrogen temperature. Nalu.re 322: 55-59.

SHE 'G, Z.Z. and A.M. HERMANN 1988. Bulk superconducting at 120 K in 'he TI-Ca-

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Data Acquisition System for Resistance Measurement of High.temperature Superconductors

Ba-Cu-O system. Na/ure 332: 138-142.

WU, M.K., JR. ASHBURI', C.J TORNG, P.H. HOR, R.L. MENG, L. GAO, Z.JHUANG, Y.Q. WANG and C.W. CHU. 1987. Superconductivity at 93 K in a newmixed-phase Y·Ba-Cu-O compound system at ambient pressure. Phys. Rev. Lett. 58:908-910.

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