cu o -nano-yba zro 5.5 compositesdownloads.hindawi.com/journals/ijsu/2014/768714.pdf · wet...

Research ArticleElectrical Transport and Lowered Percolation Threshold inYBa2Cu3O7minus120575-Nano-YBa2ZrO55 Composites

Pullanhiyodan Puthiyaveedu Rejith Sukumariamma Vidyaand Jijimon Kumpukattu Thomas

Electronic Materials Research Laboratory Department of Physics Mar Ivanios College Thiruvananthapuram Kerala 695015 India

Correspondence should be addressed to Jijimon Kumpukattu Thomas jkthomasemrlyahoocom

Received 10 May 2014 Accepted 6 August 2014 Published 25 August 2014

Academic Editor Dong Qian

Copyright copy 2014 Pullanhiyodan Puthiyaveedu Rejith et alThis is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

We investigated the chemical reactivity and percolation characteristics of insulating nanocrystalline YBa2ZrO55

prepared bymodified combustion route and the YBa

2Cu3O7minus120575

superconductor composite system Structural analysis was done by using X-ray diffraction technique surface morphology of the samples was studied using scanning electron microscopy and electricaltransport measurements like critical transition temperatures (T

119888) and self-field transport critical current (J

119888) were done by using

standard four-probe technique It is found that in YBa2Cu3O7minus120575

-nano-YBa2ZrO55

composite system the superconductor andinsulator materials coexist as separate phases without any noticeable chemical reaction even after sintering at high temperaturesFurthermore percolation threshold and critical exponent are found to be 119881

119862= 03 119905 = 168 and 119906 = 27 And the analysis of the

current flow in the polycrystalline samples reveals weak link behavior in the majority of grain connections

1 Introduction

High temperature superconductors with transition tem-peratures above 77K in ceramic materials have receivedtremendous responsiveness because of their scientific andpractical potential The study of superconducting smallaggregates clusters or particles is very important from boththe fundamental and the technological standpoint [1ndash3] Itwill be significant to study the percolation and supercon-ductivity of composites involving superconductor insertedin an insulator medium Granular nature along with shortcoherence length [4] and large penetration depth [5] of hightemperature superconductors allows us to investigate thepercolation behavior fractal properties quantum size effectsthermal fluctuations and size effects on superconductivityThepercolation concept was first employed to describe super-conductors by Davidson and Tinkham [6] who analysedresistivity data of composite Nb

3SnCu wires For the growth

of high quality films the choice of substrate is vital A high119879

119888superconductor-insulator system is very difficult to obtain

without compromising the superconducting properties The

chemical nonreactivity of the substrate materials with super-conductors indicates their potential as substrates for filmdeposition The chemical compatibility of materials with thesuperconductor at the processing temperature is crucial Alsosuperconductor-insulator percolation studies are a mediumto understand the fundamental mechanism behind hightemperature superconductivity

A percolation model can be regarded as a collection ofpoints or occupied sites distributed in a space certain pairsof them are randomly linked [7] Its applications range fromtransport in amorphous and porous media and compositesto the properties of branched polymers gels complex ionicconductors and superconductors [8]There is a path betweentwo points 119860 and 119861 if a sequence beginning with 119860 andendingwith119861 can be found such that successive points in thissequence are linked This path may allow the flow of chargebetween two points if we regard the occupied sites as piecesof conductor The sites may be clustered such that pairs ofpoints belonging to the same cluster are connected but thereis no path between points belonging to different clustersCluster size (number of points in the cluster) increases

Hindawi Publishing CorporationInternational Journal of SuperconductivityVolume 2014 Article ID 768714 7 pageshttpdxdoiorg1011552014768714

2 International Journal of Superconductivity

with the number of linkages Some cluster may become ofinfinite size at some critical density of occupied sites Abovethis critical density known as percolation threshold (119881

119904)

the infinite cluster spans entire system and the system isin percolating state For instance in an ideal mixture ofconducting and insulator particles the conductivity is zerooutside the percolating region whereas it takes a finite valueinside this region

It was reported that perovskites could be beneficialfor incorporation into YBCO due to their similar crystalstructures relative to the host YBCO phase [9] There-after perovskite based additions have gained renewed inter-est as a class of materials that can be incorporated intoREBCO superconductor for dramatic improvements in thepinning properties [10ndash13] And a number of perovskiteslike Sr

2HoHfO

55[14] GdBa

2NbO6[15] Ba

2ErZrO

55[16]

YBa2ZrO55

[17] and so forth were being considered as sub-stratematerials for YBCOfilmdepositionHowever substrateselection presents particular challenges for the productionof high-quality high-temperature superconducting (HTS)films suitable for applications [18] In order to confirm theirchemical compatibility with YBCO it is important to studythe electrical transport and percolation behavior in thesesuperconductor-insulator composites Transport propertiesand percolation behavior of high 119879

119888superconductor-metal

composites have been reported extensively [19ndash24] Thegeneral form of the double perovskites is A

2BB1015840O6 where for

the present work A = Ba B = Y and B1015840 = Zr Paulose et alstudied percolation properties of Ba

2YZrO

6prepared by con-

ventional solid state route and YBa2Cu3O7minus120575

superconductorcomposite using temperature-resistivity measurement andreported that both superconducting and normal state perco-lation threshold values of the composite are around 35 volof YBa

2Cu3O7in the system [25] In the present work the

percolation behavior and nonreactivity of nanoparticles ofYBa2ZrO55

(YBZO) ceramic prepared through an autoignit-ing combustion technique mixed with bulk YBa

2Cu3O7minus120575

(YBCO) superconductors are studied The variations in themicrostructure sintering behavior sample density electricaltransport such as 119879

119888 and current carrying capacity are also

studied

2 Materials and Methods

Conventional technique of solid state route was used forthe preparation of YBCO superconductor by which highpurity Y

2O3 BaCO

3 and CuO were thoroughly mixed in the

stoichiometric ratio of Y Ba Cu = 1 2 3 The mixture wasthen calcined at 930∘C for 72 hours with two intermediatewet grindings High quality nanoparticles of YBa

2ZrO55

(YBZO) were synthesized through modified autoignitingcombustion technique as reported by Jose et al [26] Ina typical synthesis aqueous solution containing ions of YBa and Zr was prepared by dissolving high purity Y

2O3

in dilute HNO3 Ba (NO

3)2 and ZrOCl

2(99) in double

distilled water in a glass beaker Citric acid (99) was thenadded to the solution containing Zr ions which serves asthe complexing agent Oxidantfuel ratio of the system wasadjusted by adding nitric acid and ammonium hydroxide

200nm

Figure 1 TEMmicrograph of YBa2ZrO55

nanoparticles

and the ratio was kept at unity The solution containing theprecursormixture at a pH of sim70 was heated using a hot plateatsim250∘C in a ventilated fumehoodThe combustion productwas subsequently characterized as single phase nanocrystalsof YBa

2ZrO55 The YBCO and nano-YBZO were thoroughly

mixed in different ratios and made into rectangular pelletsof dimension 12 times 4 times 1mm These pellets were sinteredat temperature ranges from 975∘C to 1500∘C for 12 hourswith a heating rate of 3∘Cminute depending on the volumepercentage of YBHO in the composite material The sampleswere then cooled to 550∘C and kept 24 hours for oxygenationand then cooled to room temperature

The structural characterization of YBCO-nanocrystallineYBZO composites was done by powder X-ray diffraction(XRD) technique using a Bruker D-8 X-ray diffractometerwithNickel filtered Cu119870

120572radiationThe surfacemorphology

of the sintered samples was studied using scanning electronmicroscopy (SEM) (JEOL JSM 6390 LV) The qualitativeand quantitative elemental composition of the materials inthe compounds was studied using energy dispersive X-rayspectroscopy (EDS) JEOLmodel JED-2300The critical tran-sition temperatures (119879

119888) of the samples were measured using

standard four-probe technique For the samples with highervol of insulator a two-probe method was used to measuretheir resistivity For this experiment the entire data collectionwas run using a Lab VIEW 71 program on a PC This wasconnected to Keithley source meter 2440 and nanovoltmeter2182A along with lakeshore temperature controller equippedwith PT-111 platinum sensor using a GPIB connection Theelectrical contacts on the surface of the pellets were doneby adhesive silver paste after making a narrow scratch onthe sample surface The self-field transport critical current(119869119888) measurements were done at liquid nitrogen temperature

using the standard 1 120583Vcm criterion

3 Results and Discussion

The powder morphology of the as-prepared YBa2ZrO55

nanopowder was done by using transmission electronmicroscopy (TEM) and is shown in Figure 1 The resultsuggested that the self-aligned nanoparticles of YBZO are ofcuboidal shape with sharp grain boundaries andwith size less

International Journal of Superconductivity 3

20 30 40 50 60 70

2120579 (deg)

(f)

(e)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

203

210

014

114

115

400 223

413

406 420

lowast220

lowast400

lowast420

lowast422

lowast440

(f)

(e)

(d)

(c)

(b)

(a)

203

210

014

114

115

400 223

413

406 420

lowastlowast220

lowast400

lowast420

lowast422

lowast440

Figure 2 XRD pattern of different vol of nano-YBZOmixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)

than 20 nm The selected area electron diffraction (SAED)pattern shown inset to Figure 1 reveals that the YBa

2ZrO55

nanoparticles were crystallized with bright polycrystallinediffraction rings SAED patterns were composed of a numberof bright spots arranged in concentric rings The electronswere reflected and diffracted from crystallographic planesof the unit cells of the sample to produce bright spots Therings were diffuse and hollow showing that the products werecomposed of nanocrystals with different orientations Thisis indicative of the polycrystalline nature of the crystallitesbut the spotty nature of the SAED pattern could be dueto the fact that finer crystallites with related orientationswere agglomerated together resulting in a limited set oforientations

The X-ray diffraction (XRD) patterns of composites for0ndash100 vol of nano-YBZO in the YBCO system are shownin Figure 2 XRD patterns of composites show that all thepeaks could be indexed for orthorhombic YBa

2Cu3O7minus120575

andcubic YBa

2ZrO55

and there is no extra peak detectable Thisimplies that YBa

2ZrO55

and YBa2Cu3O7minus120575

remain as twodifferent separate phases in the composite even after severeheat treatment up to 1020∘C For YBCO-YBZO compositeswith 80 vol YBZO the sintering temperature was above theperitectic temperature of YBCO (sim1030∘C) and therefore theformation of a 211 phase with YBCO is expected but in thepresent study the XRD patterns did not show the presence ofa 211 phase in the system Thus the composites synthesizedare suitable for the percolation studies

The surface morphology of the composite samples wasillustrated by scanning electron microscopy (SEM) Figure 3shows the SEM images of different vol of nano-YBZOadded YBCO composites These indicate that the surface ofthe samples presents a crystalline character which is typical ofa polycrystalline ceramic material The YBa

2Cu3O7minus120575

grainsform groups which have appearance of clusters and thereis no detectable interface interaction between the YBZOand YBCO grains However there are different grain sizes

and a random orientation of grain boundaries whereby thepresence of different intergrain conductivities is expected

The effect of YBa2ZrO55

on the superconducting tran-sition temperature 119879

119888of YBa

2Cu3O7minus120575

was studied by fourprobe measurements for temperatures ranging from 77 to300K Variation of normalized resistivity with temperatureof the YBCO superconductor mixed with different volof insulating nano-YBZO samples is shown in Figure 4It is observed that the composite sample with less than50 vol of YBCO showed a metallic behavior and gave zeroresistivity superconducting transition temperature above liq-uid nitrogen temperature However the YBCO-nano-YBZOcomposite with 80 vol of YBZO showed a conductingbehavior there is no superconducting transition up to 77KThe resistivity of composites is dominated by YBZO forvolume less than 50 of YBCO with a significant drop of120588 occurring near these values of volume The absence of asuperconducting network through the composite sample ora low vol of YBCO may be the reason for this behaviorThese results show that when YBCO is sim30 vol or abovethere are interconnected networks of superconducting grainsfor the super current to pass through the composite materialbut for lower vol of YBCO the continuous networkof superconducting grains breaks away and the resistancebecomes nearly equal to that of pure insulator Hence thevalue of percolation threshold for the YBCO-nano-YBZOcomposite sample lies between 30 and 40 vol of YBCO inthe composite

The resistivity (120588) and temperature coefficient of resis-tivity 120572 = (1120588)(119889120588119889119879) at room temperature are shownin Figure 5 as a function of vol of YBCO (119881

119878) in the

composite In the normal state YBCO behaves as a metallicconductor and shows resistivity sim10 120583Ωm However theresistivity of composites is dominated by YBa

2ZrO55

forlower vol of YBCO with a significant drop of 120588 occurringnear 30ndash50 vol The behavior of 120588 correlates with that of 120572which increases sharply towards that of YBCO starting from


(a) (b)

(c) (d)

(e) (f)

Figure 3 SEM images of different vol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)

119881

119878sim 30 vol So if we assumed that the electrical transport

behavior in YBCO-nano-YBZO composites is percolativethe percolation threshold 119881

119862is between 03 and 04 Thus

the superconducting percolation threshold and normal statepercolation threshold values of YBCO-nano-YBZO compos-ites lie in the same range The electrical properties of thesuperconductor-insulator system can be described in [27 28]

120588 = 120588

119900(119881

119878minus 119881

119862)

minus119905 for 119881119878gt 119881

119862

120588

1015840= 120588

1015840

119900(119881

119862minus 119881

119904)

119906 for 119881119862gt 119881

119878

(1)

where 120588119900and 1205881015840

119900are constants 119881

119862is the critical volume

fraction of superconductor at which 120588 changes dramaticallyand is called the percolation threshold 119881

119878is the vol of

superconducting material in the composite and 119905 and 119906 are

the critical exponent describing the transport properties ofthe composite system The values 120588

119900 1205881015840119900 119905 and 119906 are found

from the log-log plot of 120588 versus (119881119878minus 119881

119862) and 1205881015840 versus

(119881

119862minus 119881

119904) with 119881

119862= 03 The value of 119881

119862is adjusted so that

the log-log plots of 120588 and 1205881015840 give a straight lineLog-log plot of 120588 versus (119881

119878minus119881

119862) for119881

119878gt 119881

119862 is shown in

Figure 6 which gave the exponents 119905 = 168 and 120588119900= 508 120583Ω

m And Figure 7 shows the log-log plot of 1205881015840 in functionof (119881119862minus 119881

119904) for 119881

119862gt 119881

119878system which gave the values

119906 = 27 and 1205881015840119900= 5831 times 104 120583Ω m Least square fits were

performed to determine the slope of the plots which gavethe values of exponents 119905 and 119906 However for an idealizedmetal-insulator system 119905 = 17 and 119906 = 07 [29] A greatnumber of experiments on conducting-insulator systemsshow percolation thresholds in agreement with percolation

International Journal of Superconductivity 5N

orm

alise

d re

sistiv

ity (120588

120588r)

10

05

00

50 100 150 200 250 300

Temperature (K)

(a)

50 100 150 200 250 300

Temperature (K)

10

05

00

(b)

10

05

00

(c)

50 100 150 200 250 300

Temperature (K)

10

05

00

(d)

50 100 150 200 250 300

Temperature (K)

10

09

08

07

(e)

50 100 150 200 250 300

Temperature (K)

Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)

theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]

The values of critical current densities (119869119888) measured for

different samples at zero applied magnetic field are shownin Table 1 The self-field 119869

119888is found to be decreasing on

the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869

119888

is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path

YBa2Cu3O7minus120575

superconductor will start to melt anddecompose when it is sintered at higher temperature

40

35

30

25

20

15

10

0500 02 04 06 08 10

50

45

40

35

30

25

20

15

Vol of YBCO

Tem

pera

ture

coeffi

cien

t of r

esist

ivity

(120572)

log 120588

(120583Ω

m)

Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO

20

18

16

14

12

10

minus07 minus06 minus05 minus04 minus03 minus02 minus01

t = 168 1205880 = 508 120583Ωmlo

g 120588(120583Ω

m)

Vc = 03

log(VS minus VC)

Figure 6 Log-log plot of 120588 versus (119881119878minus 119881

119862)

40

38

36

34

32

30minus10 minus09 minus08 minus07

u = 27 1205889984000 = 5831 times 104 120583Ωm

log 120588

998400(120583Ω

m)

Vc = 03

log(VC minus VS)


119878)


Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites

Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879

119888(K) Self-field 119869

119888(times104 Acm2)

100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash

The values of 119881119862 119905 and 119906 obtained for different systems

of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions

4 Conclusion

In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa

2Cu3O7minus120575

superconductor-nano-YBa

2ZrO55

composite From structural analysis it isobserved that the mixture of materials YBa

2ZrO55

insulatorwith YBa

2Cu3O7minus120575

superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881

119862= 03 and critical exponents values

119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

SukumariammaVidya acknowledgesCSIR for financial assis-tance

References

[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990

[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012

[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T

119888superconductorsrdquo Supercon-

ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger

ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y

1Ba2Cu

3O7minus119909

rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987

[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba

2YCu3O9minus120593

evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987

[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976

[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980

[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994

[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909

superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990

[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba

2YNbO

6nanocolumns and their contribution to

flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied

Physics Express vol 3 no 2 Article ID 023101 2010


[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575

nanocomposite films with a Ba2YTaO

6secondary phase for

improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012

[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO

2add


superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014

[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874

7minus120575filmsrdquo Superconductor Science and Technology

vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino

Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr

2HoHfO

55for its use

as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001

[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa

2NbO6 a new ceramic substrate for YBCO thick filmsrdquo

Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal

structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba

2ErZrO

55rdquoMateri-

als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and

A D Damodaran ldquoSynthesis of Ba2YZrO

6 a new phase in

YBa2Cu3O7-ZrO2system and its suitability as a substrate

material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992

[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996

[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa

2NbO6nanopowders an effective percolation network

medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013

[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa

2Cu3O7minus120575

-Ba2GdNbO

6composite systemrdquo Journal of

Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998

[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa

2SbO6-YBa2Cu3O7minus120575

composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995

[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO

55as a potential substrate material for


superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007

[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr

2SbO6YBa2Cu3O7minus120575

complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004

[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba

2NdSbO

6complex perovskite as

a substrate for YBa2Cu3O7minus120575

superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006

[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba

2YZrO

6YBa2Cu3O7compos-

itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993

[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa

2ZrO55

powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999

[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al

2O3-Bi2Sr18Ca12Cu2Oy and MgO-

Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp

455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W

Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3

Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory

Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-

olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997

Submit your manuscripts athttpwwwhindawicom

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ThermodynamicsJournal of


with the number of linkages Some cluster may become ofinfinite size at some critical density of occupied sites Abovethis critical density known as percolation threshold (119881

119904)

the infinite cluster spans entire system and the system isin percolating state For instance in an ideal mixture ofconducting and insulator particles the conductivity is zerooutside the percolating region whereas it takes a finite valueinside this region

It was reported that perovskites could be beneficialfor incorporation into YBCO due to their similar crystalstructures relative to the host YBCO phase [9] There-after perovskite based additions have gained renewed inter-est as a class of materials that can be incorporated intoREBCO superconductor for dramatic improvements in thepinning properties [10ndash13] And a number of perovskiteslike Sr

2HoHfO

55[14] GdBa

2NbO6[15] Ba

2ErZrO

55[16]

YBa2ZrO55

[17] and so forth were being considered as sub-stratematerials for YBCOfilmdepositionHowever substrateselection presents particular challenges for the productionof high-quality high-temperature superconducting (HTS)films suitable for applications [18] In order to confirm theirchemical compatibility with YBCO it is important to studythe electrical transport and percolation behavior in thesesuperconductor-insulator composites Transport propertiesand percolation behavior of high 119879

119888superconductor-metal

composites have been reported extensively [19ndash24] Thegeneral form of the double perovskites is A

2BB1015840O6 where for

the present work A = Ba B = Y and B1015840 = Zr Paulose et alstudied percolation properties of Ba

2YZrO

6prepared by con-

ventional solid state route and YBa2Cu3O7minus120575

superconductorcomposite using temperature-resistivity measurement andreported that both superconducting and normal state perco-lation threshold values of the composite are around 35 volof YBa

2Cu3O7in the system [25] In the present work the

percolation behavior and nonreactivity of nanoparticles ofYBa2ZrO55

(YBZO) ceramic prepared through an autoignit-ing combustion technique mixed with bulk YBa

2Cu3O7minus120575

(YBCO) superconductors are studied The variations in themicrostructure sintering behavior sample density electricaltransport such as 119879

119888 and current carrying capacity are also

studied

2 Materials and Methods

Conventional technique of solid state route was used forthe preparation of YBCO superconductor by which highpurity Y

2O3 BaCO

3 and CuO were thoroughly mixed in the

stoichiometric ratio of Y Ba Cu = 1 2 3 The mixture wasthen calcined at 930∘C for 72 hours with two intermediatewet grindings High quality nanoparticles of YBa

2ZrO55

(YBZO) were synthesized through modified autoignitingcombustion technique as reported by Jose et al [26] Ina typical synthesis aqueous solution containing ions of YBa and Zr was prepared by dissolving high purity Y

2O3

in dilute HNO3 Ba (NO

3)2 and ZrOCl

2(99) in double

distilled water in a glass beaker Citric acid (99) was thenadded to the solution containing Zr ions which serves asthe complexing agent Oxidantfuel ratio of the system wasadjusted by adding nitric acid and ammonium hydroxide

200nm

Figure 1 TEMmicrograph of YBa2ZrO55

nanoparticles

and the ratio was kept at unity The solution containing theprecursormixture at a pH of sim70 was heated using a hot plateatsim250∘C in a ventilated fumehoodThe combustion productwas subsequently characterized as single phase nanocrystalsof YBa

2ZrO55 The YBCO and nano-YBZO were thoroughly

mixed in different ratios and made into rectangular pelletsof dimension 12 times 4 times 1mm These pellets were sinteredat temperature ranges from 975∘C to 1500∘C for 12 hourswith a heating rate of 3∘Cminute depending on the volumepercentage of YBHO in the composite material The sampleswere then cooled to 550∘C and kept 24 hours for oxygenationand then cooled to room temperature

The structural characterization of YBCO-nanocrystallineYBZO composites was done by powder X-ray diffraction(XRD) technique using a Bruker D-8 X-ray diffractometerwithNickel filtered Cu119870

120572radiationThe surfacemorphology

of the sintered samples was studied using scanning electronmicroscopy (SEM) (JEOL JSM 6390 LV) The qualitativeand quantitative elemental composition of the materials inthe compounds was studied using energy dispersive X-rayspectroscopy (EDS) JEOLmodel JED-2300The critical tran-sition temperatures (119879

119888) of the samples were measured using

standard four-probe technique For the samples with highervol of insulator a two-probe method was used to measuretheir resistivity For this experiment the entire data collectionwas run using a Lab VIEW 71 program on a PC This wasconnected to Keithley source meter 2440 and nanovoltmeter2182A along with lakeshore temperature controller equippedwith PT-111 platinum sensor using a GPIB connection Theelectrical contacts on the surface of the pellets were doneby adhesive silver paste after making a narrow scratch onthe sample surface The self-field transport critical current(119869119888) measurements were done at liquid nitrogen temperature

using the standard 1 120583Vcm criterion

3 Results and Discussion

The powder morphology of the as-prepared YBa2ZrO55

nanopowder was done by using transmission electronmicroscopy (TEM) and is shown in Figure 1 The resultsuggested that the self-aligned nanoparticles of YBZO are ofcuboidal shape with sharp grain boundaries andwith size less


20 30 40 50 60 70

2120579 (deg)

(f)

(e)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

203

210

014

114

115

400 223

413

406 420

lowast220

lowast400

lowast420

lowast422

lowast440

(f)

(e)

(d)

(c)

(b)

(a)

203

210

014

114

115

400 223

413

406 420

lowastlowast220

lowast400

lowast420

lowast422

lowast440



2ZrO55



2Cu3O7minus120575

andcubic YBa

2ZrO55


2ZrO55




2Cu3O7minus120575





119888of YBa

2Cu3O7minus120575



119878) in the


2ZrO55



(a) (b)

(c) (d)

(e) (f)


119881





120588 = 120588

119900(119881

119878minus 119881

119862)

minus119905 for 119881119878gt 119881

119862

120588

1015840= 120588

1015840

119900(119881

119862minus 119881

119904)

119906 for 119881119862gt 119881

119878

(1)

where 120588119900and 1205881015840




119878is the vol of



119900 1205881015840119900 119905 and 119906 are found


119862) and 1205881015840 versus

(119881

119862minus 119881

119904) with 119881

119862= 03 The value of 119881



119878minus119881

119862) for119881

119878gt 119881

119862 is shown in



119904) for 119881

119862gt 119881





orm

alise

d re

sistiv

ity (120588

120588r)

10

05

00

50 100 150 200 250 300

Temperature (K)

(a)

50 100 150 200 250 300

Temperature (K)

10

05

00

(b)

10

05

00

(c)

50 100 150 200 250 300

Temperature (K)

10

05

00

(d)

50 100 150 200 250 300

Temperature (K)

10

09

08

07

(e)

50 100 150 200 250 300

Temperature (K)







119888




40

35

30

25

20

15

10

0500 02 04 06 08 10

50

45

40

35

30

25

20

15

Vol of YBCO

Tem

pera

ture

coeffi

cien

t of r

esist

ivity

(120572)

log 120588

(120583Ω

m)


20

18

16

14

12

10


t = 168 1205880 = 508 120583Ωmlo

g 120588(120583Ω

m)

Vc = 03

log(VS minus VC)


119862)

40

38

36

34

32


u = 27 1205889984000 = 5831 times 104 120583Ωm

log 120588

998400(120583Ω

m)

Vc = 03

log(VC minus VS)


119878)




119888(K) Self-field 119869

119888(times104 Acm2)




4 Conclusion


2Cu3O7minus120575


2ZrO55


2ZrO55

insulatorwith YBa

2Cu3O7minus120575






Acknowledgment


References







1Ba2Cu

3O7minus119909



2YCu3O9minus120593








2YNbO










2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




20 30 40 50 60 70

2120579 (deg)

(f)

(e)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

203

210

014

114

115

400 223

413

406 420

lowast220

lowast400

lowast420

lowast422

lowast440

(f)

(e)

(d)

(c)

(b)

(a)

203

210

014

114

115

400 223

413

406 420

lowastlowast220

lowast400

lowast420

lowast422

lowast440



2ZrO55



2Cu3O7minus120575

andcubic YBa

2ZrO55


2ZrO55




2Cu3O7minus120575





119888of YBa

2Cu3O7minus120575



119878) in the


2ZrO55



(a) (b)

(c) (d)

(e) (f)


119881





120588 = 120588

119900(119881

119878minus 119881

119862)

minus119905 for 119881119878gt 119881

119862

120588

1015840= 120588

1015840

119900(119881

119862minus 119881

119904)

119906 for 119881119862gt 119881

119878

(1)

where 120588119900and 1205881015840




119878is the vol of



119900 1205881015840119900 119905 and 119906 are found


119862) and 1205881015840 versus

(119881

119862minus 119881

119904) with 119881

119862= 03 The value of 119881



119878minus119881

119862) for119881

119878gt 119881

119862 is shown in



119904) for 119881

119862gt 119881





orm

alise

d re

sistiv

ity (120588

120588r)

10

05

00

50 100 150 200 250 300

Temperature (K)

(a)

50 100 150 200 250 300

Temperature (K)

10

05

00

(b)

10

05

00

(c)

50 100 150 200 250 300

Temperature (K)

10

05

00

(d)

50 100 150 200 250 300

Temperature (K)

10

09

08

07

(e)

50 100 150 200 250 300

Temperature (K)







119888




40

35

30

25

20

15

10

0500 02 04 06 08 10

50

45

40

35

30

25

20

15

Vol of YBCO

Tem

pera

ture

coeffi

cien

t of r

esist

ivity

(120572)

log 120588

(120583Ω

m)


20

18

16

14

12

10


t = 168 1205880 = 508 120583Ωmlo

g 120588(120583Ω

m)

Vc = 03

log(VS minus VC)


119862)

40

38

36

34

32


u = 27 1205889984000 = 5831 times 104 120583Ωm

log 120588

998400(120583Ω

m)

Vc = 03

log(VC minus VS)


119878)




119888(K) Self-field 119869

119888(times104 Acm2)




4 Conclusion


2Cu3O7minus120575


2ZrO55


2ZrO55

insulatorwith YBa

2Cu3O7minus120575






Acknowledgment


References







1Ba2Cu

3O7minus119909



2YCu3O9minus120593








2YNbO










2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)

(c) (d)

(e) (f)


119881





120588 = 120588

119900(119881

119878minus 119881

119862)

minus119905 for 119881119878gt 119881

119862

120588

1015840= 120588

1015840

119900(119881

119862minus 119881

119904)

119906 for 119881119862gt 119881

119878

(1)

where 120588119900and 1205881015840




119878is the vol of



119900 1205881015840119900 119905 and 119906 are found


119862) and 1205881015840 versus

(119881

119862minus 119881

119904) with 119881

119862= 03 The value of 119881



119878minus119881

119862) for119881

119878gt 119881

119862 is shown in



119904) for 119881

119862gt 119881





orm

alise

d re

sistiv

ity (120588

120588r)

10

05

00

50 100 150 200 250 300

Temperature (K)

(a)

50 100 150 200 250 300

Temperature (K)

10

05

00

(b)

10

05

00

(c)

50 100 150 200 250 300

Temperature (K)

10

05

00

(d)

50 100 150 200 250 300

Temperature (K)

10

09

08

07

(e)

50 100 150 200 250 300

Temperature (K)







119888




40

35

30

25

20

15

10

0500 02 04 06 08 10

50

45

40

35

30

25

20

15

Vol of YBCO

Tem

pera

ture

coeffi

cien

t of r

esist

ivity

(120572)

log 120588

(120583Ω

m)


20

18

16

14

12

10


t = 168 1205880 = 508 120583Ωmlo

g 120588(120583Ω

m)

Vc = 03

log(VS minus VC)


119862)

40

38

36

34

32


u = 27 1205889984000 = 5831 times 104 120583Ωm

log 120588

998400(120583Ω

m)

Vc = 03

log(VC minus VS)


119878)




119888(K) Self-field 119869

119888(times104 Acm2)




4 Conclusion


2Cu3O7minus120575


2ZrO55


2ZrO55

insulatorwith YBa

2Cu3O7minus120575






Acknowledgment


References







1Ba2Cu

3O7minus119909



2YCu3O9minus120593








2YNbO










2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




orm

alise

d re

sistiv

ity (120588

120588r)

10

05

00

50 100 150 200 250 300

Temperature (K)

(a)

50 100 150 200 250 300

Temperature (K)

10

05

00

(b)

10

05

00

(c)

50 100 150 200 250 300

Temperature (K)

10

05

00

(d)

50 100 150 200 250 300

Temperature (K)

10

09

08

07

(e)

50 100 150 200 250 300

Temperature (K)







119888




40

35

30

25

20

15

10

0500 02 04 06 08 10

50

45

40

35

30

25

20

15

Vol of YBCO

Tem

pera

ture

coeffi

cien

t of r

esist

ivity

(120572)

log 120588

(120583Ω

m)


20

18

16

14

12

10


t = 168 1205880 = 508 120583Ωmlo

g 120588(120583Ω

m)

Vc = 03

log(VS minus VC)


119862)

40

38

36

34

32


u = 27 1205889984000 = 5831 times 104 120583Ωm

log 120588

998400(120583Ω

m)

Vc = 03

log(VC minus VS)


119878)




119888(K) Self-field 119869

119888(times104 Acm2)




4 Conclusion


2Cu3O7minus120575


2ZrO55


2ZrO55

insulatorwith YBa

2Cu3O7minus120575






Acknowledgment


References







1Ba2Cu

3O7minus119909



2YCu3O9minus120593








2YNbO










2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics






119888(K) Self-field 119869

119888(times104 Acm2)




4 Conclusion


2Cu3O7minus120575


2ZrO55


2ZrO55

insulatorwith YBa

2Cu3O7minus120575






Acknowledgment


References







1Ba2Cu

3O7minus119909



2YCu3O9minus120593








2YNbO










2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics









2add







2HoHfO

55for its use






2ErZrO

55rdquoMateri-



6 a new phase in








2Cu3O7minus120575

-Ba2GdNbO














2NdSbO





2YZrO

6YBa2Cu3O7compos-



2ZrO55















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics








FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



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