(10,11)ceramic glass superconductors1 s2.0 s0925838804006863 main

Journal of Alloys and Compounds 385 (2004) 3343

Synthesis and characterization of Er-substituted Bi-2223 H-Tcglassceramic superconductors

Mehmet Ali Aksan, Mehmet Eyyphan YakinciInn niversitesi, Fen Edb. Fakltesi, Fizik Blm, 44069 Malatya, Turkey

Received 15 September 2003; received in revised form 20 April 2004; accepted 22 April 2004

Abstract

The Bi2Sr2Ca2Cu3xErxO10+ (x = 0.5 and 1.0) H-Tc system was prepared by glassceramic technique to investigate the microstructuralformation, thermal and transport properties. We have found that Er+3 ions have a solid solubility limit in the Bi-2223 system and this limit waspassed at x = 1.0. Below this limit glass samples were prepared and converted to the glassceramic form easily, but after the solid solubilitylimit glass formation was diminished and crystallized samples were formed after melt quenching. The substitution had considerable effecton the electrical properties comparing with the unsubstituted Bi-2223 material. The Tc values of the x = 0.5 and 1.0 sample were found tobe 71 0.1 K. The thermoelectric power data were analyzed in view of two band model with linear T-term and Xins two band model.Thermoelectric power was obtained to be positive for the both samples, indicating that the hole type conductivity is dominant in the materialsprepared. The magnitude of thermal conductivity, , was also influenced by the Er concentration. When the Er concentration was increasedthe magnitude of was suppressed. It strongly indicates that the impurities play a significant role in limiting the heat transport due to a strongincrease of the electronphonon-impurity scattering rate. 2004 Elsevier B.V. All rights reserved.

Keywords: Er-substituted Bi-2223; Glassceramic superconductors; BSCCO system; Thermal conductivity; Thermoelectric power

1. Introduction

It is interesting to alter the electronic structure of theCuO2 planes by substitutions and thus the superconduct-ing behavior of BSCCO system. Substitutions indicateda dramatic effect on the Tc values of the systems. It hasbeen clearly seen that there are no significant differencesin the strengths of Tc suppression between magnetic andnon-magnetic substitutions in the BSCCO materials [1,2].It should be emphasized that the Tc values of the systemsprepared decreased due to the impurities which cause thescattering of the carriers in the CuO planes and/or due tothe variation of the carrier concentration by substitutions[39]. The suppression of Tc due to the substitution of theother elements for Cu has been attributed to the Abrikosovand Gor kov pair breaking mechanism [10,11]. An increaseor decrease in the hole concentration in the CuO2 planesand carrier localization induced by the structural disordersare also useful to explain the decrease in Tc [12,13].

Corresponding author.E-mail address: [email protected] (M.A. Aksan).

Thermoelectric power (TEP) investigation in solids isone of the basic tools to understand the nature of chargecarriers which are responsible for the conduction process.There have been many studies done on the TEP propertiesof the high-Tc glassceramic BSCCO material. In most ofthem, substitution effect on TEP properties, particularly forthe Bi-site, have been investigated [10,11,1419]. Most ofthe works indicated either positive or negative TEP prop-erties depending on the compositions and doping level orpreparation conditions. However, there exist few works onsubstituting other elements, such as Fe and Ti, for Cu par-ticularly in the glassceramic BSCCO system [10,15,16].The most important observation is that the underdoped sys-tems have positive and large TEP value which also showstemperature-independent nature particularly at high temper-atures, whereas the overdoped systems have negative andsmall TEP values and varies almost linearly with tempera-tures. However, for the optimum carrier concentration case,the value of TEP increases with temperature and reachesthe maximum at around Tc and then decreases. For theTEP investigations on high-Tc materials, some importantmodels have been developed. But, no consensus has been

0925-8388/$ see front matter 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.jallcom.2004.04.135

34 M.A. Aksan, M.E. Yakinci / Journal of Alloys and Compounds 385 (2004) 3343

attained among the models developed. Some models havebeen particularly used for high-Tc BSCCO materials, whichare: two band model with linear T-term [20]; NagosaLeemodel [21]; phenomenological narrow band model [22];Xins two band model [23]; three-state model [24]; andHubbardHamiltonian model [25].

Thermal conductivity, (T), investigation also gives im-portant information about the scattering mechanism ofcharge carriers, electronphonon interaction and other phys-ical properties such as carrier density and phonon mean freepath [2631]. In the last decade, there were many investiga-tions have been made on (T) of high-Tc materials [2637]and almost the same results were obtained. In general, for(T) investigation of high-Tc materials three important ap-proaches can be considered to the total (T) calculations: (i)phonon contribution; (ii) electron contribution; and (iii) bothelectron and phonon contributions. Many research groupshave investigated these valuable approaches for high-Tcmaterials and results were reported [27,3235,3841].

However, there exits a difficulty on the (T) propertiesof the high-Tc materials. In particular, compared with con-ventional metallic structures, the high-Tc superconductorsshow unusual behavior just below their Tc. At that point,thermal conductivity rises and reaches to the maximum andthen drops sharply. The explanation of the rapid rise andthe maximum point seen in a wide range just below Tc, issummed up the two main points [26]. Firstly, decrease onthe scattering mechanism, because of the superconductingstate (T < Tc), and secondly, an increase in the electronmean free path due to decrease in the phonon scattering.In many investigations, the value of the maximum wasalso found to depend on the preparation method and/or thechemical compositions [4247]. However, it is also impor-tant to see the effect of the quasi-particle contribution onthe rapid rise of (T) below the Tc as explained by manygroups [35,41]. There exist some other models that havebeen widely accepted for materials in solid state. Particu-larly, for the graded materials, effective medium approx-imation (EMA) [36,48,49] and another model developedparticularly for the conventional low-Tc superconductorsby Bardeen et al. [50] that describes the phonon thermalconductivity in the superconducting state. This model thengeneralized by Tewordth and Wolkhausen in order to de-scribe the phonon thermal conductivity of high-Tc super-conductors in a wide range of temperatures [39]. However,still many efforts have to be made both experimentally andtheoretically to understand the (T) mechanism of high-Tcmaterials.

In the present study, we have prepared Bi2Sr2Ca2(Cu3xErx)O10+, where x = 0.5 and 1.0, high-Tc superconduct-ing materials by glassceramic technique. There has beenno report found on the synthesis and characterization ofBi2Sr2Ca2(Cu3xErx)O10+ glassceramic system in the lit-erature and we have reported the crystallization, microstruc-ture, electrical, TEP and (T) properties of these materialsfor the first time.

2. Experimental

Glass samples with nominal compositions of Bi2Sr2Ca2Cu3xErxO10+, where x = 0.5 and 1.0, were prepared bythe glassceramic technique. High grade (99.99%) oxidepowders of Bi2O3, SrCO3, CaCO3CuO and Er2O3 weremixed mechanically for 3 h. The mixture was melted in an-alumina crucible at high temperature furnace between1050 and 1250 C for 30 min to 3 h, which depends on thecomposition. Molten mixture was poured onto a cold copperplate and pressed quickly with another cold plate. Rapidlyquenched, dark, shiny and approximately 13 mm thickamorphous materials were obtained. The glass samples pre-pared were then heated in P.I.D. controlled tube furnace inoxygen atmosphere at 850900 C for 60240 h, depend-ing on the substitution level. The optimum heat treatmentcondition of each composition was derived from XRD,SEMEDX, resistance and DTA results. The optimumconditions were found to be 890 C/240 h for the x = 0.5sample and 900 C/240 h for the x = 1.0 sample (Table 1).After x = 1.0 substitution level, no glass formation was ob-tained even at very high temperature range, 12001250 C,therefore, those samples were not investigated.

All samples prepared in this work were firstly examinedby X-ray diffraction analysis (XRD) to find out whether theywere fully amorphous or not. After heat treatment cycles,samples were also investigated by XRD analysis to find outthe structural evaluation. All XRD analysis was performedby using Rigaku RadB X-ray diffractometer with Cu Kradiation and a constant scan rate of 2 = 360 with a0.2/min scan rate.

Microstructural investigations were performed using Jeol6400 scanning electron microscope (SEM) combined withan energy dispersive X-ray analysis (EDX).

Differential thermal analysis (DTA) was used to deter-mine the nature of the phase transformations within the ma-terials prepared. During the DTA investigations 20 mg wellgrained powder of each sample was examined between roomtemperature to 1000 C using -alumina reference materialwith automated Shimadzu network system 60 equipment.

The electrical property of the samples was carried out us-ing a computer controlled four probe dc resistance measure-ment system with closed cycle He refrigerator (Leybold LT10 system). Conductive silver paint was used for contacts.

Thermoelectric power (TEP) measurements were carriedout using the closed cycle refrigerator. The samples wereclamped between two thin copper plates. One of the copperplates was placed on the cold head of the system and theother on the top of the samples. Temperature gradient (estab-lished) from the cold to the hot part of the sample was keptat T 2 K through the measurements using 25 heater.Voltages were recorded using Keithley 182 nano-voltmeterand the temperatures were monitored with two calibratedsilicon diodes. The thermal conductivity, (T), measure-ments of the glassceramic samples were performed usingsteady-state heat flow method using closed cycle refrigera-

M.A. Aksan, M.E. Yakinci / Journal of Alloys and Compounds 385 (2004) 3343 35

Table 1Summary of the preparation conditions and physical properties of the samples, optimum: optimum treatment condition, p: hole concentration value perCu atom

Material (x) Condition Heating parameters Tc (K) Tzero (K) T (K) PTemperature (C) Time (h) Atmosphere

0.5 Non-optimum 870 240 O2 44 25 19 0.2450.5 Non-optimum 880 240 O2 55 25 30 0.2370.5 Optimum 890 60 O2 64 29 35 0.2310.5 Optimum 890 120 O2 70 41 29 0.2260.5 Optimum 890 240 O2 71 46 25 0.2250.5 Non-optimum 900 240 O2

1.0 Non-optimum 880 240 O2 42 21 21 0.2461.0 Non-optimum 890 240 O2 53 22 31 0.2391.0 Optimum 900 60 O2 70 36 34 0.2281.0 Optimum 900 120 O2 70 37 33 0.2261.0 Optimum 900 240 O2 71 44 27 0.2211.0 Non-optimum 910 240 O2 1.0 Non-optimum 920 240 O2

1.5 Non-glassceramic

tor system. The bottom of the sample was fixed to the coldhead of the cryostat system and the upper part of the sam-ple was attached to a heater (25) which had an indiumsheated surface. The temperature difference was recordedusing two silicon diodes attached to the both end of thesamples.

3. Results and discussion

3.1. X-ray diffraction investigationUnder the preparation condition used, it was found

that the high-Tc phase formation largely depended on the

Fig. 1. XRD pattern of the Er-substituted samples: (a) x = 0.5 glass sample, (b) x = 1.0 glass sample, (c) x = 0.5 sample heat treated at 890 C for240 h, and (d) x = 1.0 sample heat treated at 900 C for 240 h.

heating time, as well as on the heating temperature. Incontrast with other substitutions in Bi-2223 glassceramicmaterial, such as Ga and Pb (where 100160 h thermaltreatment time at 830850 C is necessary for high-Tcphase formation [51,52]) long time (200400 h dependingon x) and high temperature (890900 C depending on x)in Er-substituted material favors the growth of the super-conducting phase (Table 1).

Fig. 1 shows the XRD patterns of the glass materialsand glassceramic samples heat treated under the opti-mum conditions. The structural data have been calculated(only for samples heat treated under their optimum condi-tions) by using the least-square fit of the X-ray lines. The


micro-qualitative data obtained from the SEMEDX havebeen taken into account.

The XRD pattern of x = 0.5 and 1.0 Er-subtituted glasssamples are shown in Fig. 1a and b, respectively. A largehalo was obtained at around 2 = 30, which is a funda-mental characteristics of the glass material, indicates theshort-range atomic order and the absence of periodicity inthe three-dimensional network.

Fig. 1c shows the XRD pattern of the x = 0.5 sample heattreated at 890 C for 240 h (optimum condition). The sam-ple consists mainly of the Bi1.95Sr1.98Ca0.9Cu1.3Er0.42O8+phase and this is close to the Bi-2212 superconductingphase. However, a small amount of the Bi-2223 supercon-ducting phase was also obtained without any Er concentra-tion. The impurity (solid solution) phases were identifiedas Cu2Er2O5 and Bi6Ca7O16. The crystal symmetry wasfound to be tetragonal and the unit cell parameters werecalculated to be a (= b) = 5.4304 and c = 31.8545 . Infact, these parameters were found slightly different than theBi-2212 phase (a (= b) = 5.3941 and c = 30.6013 )[53].

For the x = 1.0 sample after the heat treatment at 900 Cfor 240 h as its optimum condition, a slight change oc-curred in the main XRD pattern, Fig. 1d. In conjunctionwith the SEMEDX analysis, the main phase was found tobe Bi1.94Sr1.97Ca0.9Cu0.9Er0.89O8+. The peak intensity ofthe Cu2Er2O5 phase increased at least twice compared to x= 0.5 sample. The Bi6Ca7O16 impurity phase was also ob-tained. In this sample, the tetragonal symmetry of the mainphase remained unchanged and had unit-cell constants a(= b) = 5.8230 and c = 31.5132 , indicating a decreasein the c-axis and an increase in the a-axis.

In general, substitution of Er has an effect on the CuObond length and therefore the unit cell parameters. The in-crease of the a-axis and the decrease of the c-axis are be-lieved to be due to incorporation of Er ions into the interstitial

Fig. 2. The surface morphologies of the samples for: (a) x = 0.5 and (b) 1.0 after being heat treated at their optimum condition.

sites in the unit cell rather than occupation of the Cu sites.Also, it is said that the atomic radius of Er3+ (r = 0.88 )is bigger than Cu2+ (r = 0.72 ) atoms. If one can sup-pose the valance state of the Er ions is 3+ and remains un-changed in the matrix, it is inevitable that a distorted bandstructure and thus a change on the unit cell dimension. How-ever, to clarify this point at least Notron diffraction data orhigh-resolution transmission electron microscope (HTEM)work must be done.

3.2. Scanning electron microscopy (SEM) and energydispersive X-ray analysis (EDX)

The surface morphology and microanalysis of the sampleshave been examined by SEM and EDX analysis. The surfacemorphologies of the samples for x = 0.5 and 1.0 after heattreated at their optimum condition are shown in Fig. 2a andb, respectively. As seen in Fig. 2a, for the x = 0.5 sample,randomly oriented flake-like grains were obtained, which isthe typical glassceramic BSCCO structure for long timeheat treated samples.

In the case of the x = 1.0 samples, slightly different sur-face morphology was obtained, Fig. 2b. Most of the flakygrains have formed smaller than the x = 0.5 sample, butsome grains formed as 250300m long whiskers. TheEDX analyses of whisker were showed single phase Bi-2212composition without any contaminations.

The micro-qualitative analysis, the EDX result of polishedsurface, of the x = 0.5 sample showed that the sample con-sists of four different phases, Bi1.95Sr1.98Ca0.9Cu1.3Er0.42O8+, Bi-2223, Cu2Er2O5 and Bi6Ca7O16 as denotedzone 14 in Fig. 3a. In the case of the x = 1.0 sam-ples, the EDX analysis showed that the main phase wasBi1.94Sr1.97Ca0.9Cu0.9Er0.89O8+, the previously obtainedphases were grown together in the main matrix with similarcomposition, Fig. 3b.


Fig. 3. Polished surface morphology of the samples for: (a) x = 0.5 and (b) 1.0 after being heat treated at their optimum condition; (1) denotesBi1.95Sr1.98Ca0.9Cu1.3Er0.42O8+ in the x = 0.5 sample/Bi1.94Sr1.97Ca0.9Cu0.9Er0.89O8+ in the x = 1.0 sample, (2) Bi-2223, (3) Cu2Er2O5, and (4)Bi6Ca7O16.

3.3. Differential thermal analysis (DTA) investigation

One of the important benefits of the thermal analysisexperiment is its usefulness in selecting appropriate (heattreatment) temperatures for the heat treatment cycles of theglassceramic materials as well as for the investigation ofthe phase development.

The DTA curves of the x = 0.5 and 1.0 Er substitutedsamples are shown in Fig. 4. A standard heating rate, = 10 C/min, was used during the experiments. Before thecrystallization peak temperature an endothermic activity wasobtained at 490 C for both x = 0.5 and 1.0 samples. Thisis the characteristic property of glass material as obtainedin the conventional glass samples, which is suggested thatboth materials are in the glass form.

For the x = 0.5 Er-substituted sample, two exothermicpeaks were obtained at 509 and 547 C, Fig. 4a. The firstpeak at 509 C corresponds to the nucleation assisted crystal-lization process, and the second peak at 547 C indicates theformation of the impurity phases such as Cu2Er2O5 and/orBi6Ca7O16. The exothermic activities at 781 and 890 Ccorrespond to the formation of the Bi-2201 and Bi-2212phases.

Similar thermal activities have been obtained for the x= 1.0 sample. However, the peak temperatures increased ap-proximately 10 C, except the new peak obtained at 499 Cwhich is believed that large nucleation centers occur initiallyand then convert rapidly to a crystalline form (Fig. 4b).

In general, basic properties of glass to glassceramicphase transition have been obtained for both samples. Com-pared with the unsubstituted Bi-2223 material, no partialmelting activities (an endothermic dip which promotes sin-gle phase crystal growth in BSCCO) were obtained between830 and 850 C. It is known widely that Er is an infusibleelement particularly in the conventional glassceramic

matrices and that it is very difficult to prepare glass materialif high Er concentrations used in the initial batch [54].

In this work, we attempted to prepare glass sample withhigh Er concentration, but failed. This suggests that the solidsolubility of Er in the Bi-2223 system is limited.

3.4. Electrical properties

The electrical resistance (RT) properties of the samplesprepared are summarized in Table 1 and RT plots of selectedsamples are given in Fig. 5.

As shown in Fig. 5a, x = 0.5 sample after the heat treat-ment at optimum condition, has metallic behavior from roomtemperature to the Tc value. The critical temperature, Tc,was found to be 71 0.1 K and the zero resistance was ob-tained at Tzero, 46 0.1 K.

The x = 1.0 Er-substituted sample, heat treated at 900 Cfor 60 h, showed a semiconducting behavior from room tem-perature to the Tc value, Fig. 5b. The superconducting be-havior started at 70 0.1 K and the Tzero value was reachedat 36 0.1 K. However, when the heat treatment time ofx = 1.0 sample extended to 240 h at the same temperature(optimum condition), the electrical behavior changes signif-icantly and metallic property was obtained (Fig. 5c). The Tcand Tzero values were found to be 71 0.1 and 44 0.1 K,respectively.

In general, it is found that superconducting property ofthe samples decreases if the Er concentration increased inthe Bi-2223 system. The results suggested that the phase co-herence of the main Bi-2223 structure may in some way bedestroyed. It is also believed that the intergrowth of impu-rity solid-solution phases in the main matrices (as obtainedby the XRD and SEM investigations) and the formation ofweak coupling between the grains play an important role indecreasing of the superconductivity.


Fig. 4. DTA curves of the samples taken at heating rate of = 10/min: (a) x = 0.5 sample and (b) x = 1.0 sample. Insert shows the temperature regionbetween 450 and 600 C.

3.5. Hole concentration

The number of holes per Cu atom has been calculatedusing the formula given by Presland et al. [55]:Tc

Tmaxc= 1 82.6(P 0.16)2 (1)

where Tmaxc is taken 110 K for the Bi-2223 system and Pthe number of the holes per Cu. Recently, this equation wassuccessfully applied to the doped/substituted Bi-based su-perconducting system [5660]. Previous calculations for theunsubstituted Bi-2223 material had shown that the P-valueranged from 0.116 to 0.16. In this work, the P-value of thex = 0.5 and 1.0 samples (after the heat treatment under theoptimum) has been calculated to be 0.225 and 0.221, respec-tively, Table 1. The results obtained shows that the P-valueof our samples is higher than the unsubstituted Bi-2223 sys-tem and thus our samples are in the overdoped region. Sincethe cation state of Er is 3+, extra charge transfers to the

system, hole concentration in the CuO2 planes is believedto change significantly.

3.6. Thermoelectric power (S)

The thermoelectric power, S, versus temperature plots ofx = 0.5 and 1.0 samples are shown in Fig. 6. For uniformity,S measurements have been performed only for samples afterheat treatment under their optimum conditions.

For x = 0.5 Er-substituted sample, positive S value wasobtained and decreased linearly down to 80 K and thendropped to zero at 68 K, Fig. 6a. This behavior is consistentwith the fact that S vanishes at temperature correspondingto Tc.

When Er concentration increased to x= 1.0, a positive buthigher S value was obtained, Fig. 6b. The S value decreasedlinearly down to 75 K as temperature decreased and droppedto zero at 50 K. Er-substitution affected the Tc value and itseffect on S was qualitatively similar for both samples. This


Fig. 5. The RT plots of the samples: (a) x = 0.5 sample heat treated at 890 C for 240 h (optimum condition), (b) x = 1.0 sample heat treated at 900 Cfor 60 h, and (c) x = 1.0 sample heat treated at 900 C for 240 h (optimum condition).

indicates that substitution of Er changes the distribution ofcharges between the BiO and CuO planes and it may resultin an increase in the hole concentration in the CuO plane.

As mentioned in the introduction, several theoretical mod-els have been used to explain the S behavior of high-Tc su-perconductors. The S data of the samples prepared in thiswork are analyzed in view of two-band model with linearT-term and Xin s two band model and discussion of theresults is as follow.

3.6.1. Two-band model with linear T-termAs explained by several research groups, the tempera-

ture dependence of S of high-Tc superconducting systems is

Fig. 6. Temperature dependence of thermoelectric power, S, of the x = 0.5 sample heat treated at 890 C for 240 h and for the x = 1.0 sample heattreated at 900 C for 240 h.

similar to that of mixed valance and heavy Fermion system[20,57,61].

Forro et al. [20,61] have tried to fit their single crystalBi-2212 data using the formula explained by Gottwick et al.[62]:

S = ATB2 + T 2 (2)

A = 2E0 EFe

B2 = 3 (E0 EF)2 + 2

2k2B, (3)

where E0 is the center of the resonance and the width of theresonance. The main idea in this theory is that superimposed


Fig. 7. The fitting of two band model with linear T-term to the S data ofthe samples. Solid lines show fitting curves.

on a broad band, there is localized peak density of states nearthe Fermi level. This resonance peak gives the characteristictemperature dependence of S. Forro et al. then added a linearterm to Eq. (2) to obtain the best fit of S data [20].

S = ATB2 + T 2 + T (4)

where T represents normal band contribution. The Eq. (4)has been fitted successfully to the S data of Bi-based high-Tcsuperconductors by many research groups [5759].

The S results of our samples fitted to Eq. (4) in the tem-perature range of 90270 K are shown in Fig. 7. The fittingparameters A, B, , (E0 EF) and are given in Table 2.The experimental points of x = 0.5 sample fit well withEq. (4). But this is not the case for x = 1.0 sample. A and(E0 EF) values increased by increasing x. This suggeststhat Fermi level should go down relatively to the top of theband with increasing hole density in the system, while the(E0 EF) value increases with x in the system. This is incontradiction to the expected result. The result indicates thatthe normal band contribution, T, decreases with increasingthe substitution of Er.

3.6.2. Xin s two band modelThe investigation of two-band model by Xin et al. on

Tl-based high-Tc materials indicates that S comes from the

Table 2The fit parameters, A, B, and the estimated values of (E0 EF) and of the systemX-value A (V) B (K) (V/K2) E0 EF (K) (K)0.5 41.8234 448.605 5.16885 103 0.243 813.681.0 820.513 263.916 1.07018 103 4.76 478.67

Table 3The fit parameters, D, E, and F and the estimated values of Eg

X-value D (V/K2) E (V/K2) (K) F (V/K2) Eg (eV)0.5 29.4783 29.4449 0.0203848 29.473 3.516378 1061.0 586.635 582.739 0.630883 586.634 108.8273 106

combination of both the conduction and valance band car-riers [23]. This model is then applied successfully to theBi-based systems due to the structural similarity betweenBi and Tl based high-Tc materials by many research groups[5759,6365]. In the two-band model for Bi-2223 sys-tem, it must be considered that one band is formed by theCuO planes, which contribute to the metallic conductionof holes and the other by the BiO planes that contributeto the semiconductor-like behavior of electrons. For such atwo-band model the total S can be described by [66]

S = (S++ + S)

(5)

where = + + is the sum of the conductivitiesby electrons and holes, + the electrical conductivity ofholes, the electrical conductivity of electrons and S+and S are their respective Seebeck coefficients. WhileCuO planes show metallic behavior, BiO planes displaysemiconductor-type behavior. In this case, + is propor-tional to 1/T and is proportional to exp(Ec/kT). Assuming+ , the TEP can be given by [23]:S = DT+ (E+ FT) exp

( T

)(6)

where D, E, F, and are the fitting parameters.We have also analyzed the S results of our glassceramic

samples on the basis of Eq. (6). The best fitting parametersare given in Table 3. The best fit curves of our x = 0.5 and1.0 samples are shown in Fig. 8. It has been found that theexperimental data of x = 0.5 sample is well fitted to Eq. (6)but the fitting is not good for the x = 1.0 sample.

As seen in Table 3, significant difference between thefitting parameters of both samples was found. The parameterD, which is related with the contribution of mobile holesin the CuO planes, has been increased significantly for x= 1.0 sample (higher Er concentration case). An increaseon the D value indicates an increase in the number of themobile holes in the CuO planes [23,6365].

The experimentally determined value of was usedto evaluate the energy gap in the band structure for theBiO layers. By considering the relations = Ec/kB andEc = Eg/2, the energy gap is calculated to be 3.516378 106 eV and 108.8273 106 eV for the x = 0.5 and


Fig. 8. The fitting of Xins two band model to the S data of samples. Solid lines show fitting curves.

1.0 samples, respectively, which is consistent with thoseobtained from scanning-tunneling spectroscopy studies onBi-based system [67,68]. However, a difference betweenthe Eg values of the samples were noticed. Therefore, thechange of , where depends of the energy gap betweenBiO band and conduction band, indicates the change ofthis band gap significantly. Possible cause of this change inthe band gap is the increase in impurity concentration inthe sample. In addition to that, the excess oxygen atoms in-corporating into the BiO layers with the substitution mayalso have an effect on the change of energy band gap.

3.7. Thermal conductivity (T)

The variation of the thermal conductivity with temper-ature, (T), for samples heat treated under their optimum

Fig. 9. Temperature dependence of thermal conductivity, , of the x = 0.5 sample heat treated at 890 C for 240 h (optimum condition) and for the x= 1.0 sample heat treated at 900 C for 240 h (optimum condition).

condition are shown in Fig. 9. In the metallic state (T > Tc)for both samples, was decreased linearly as temperaturedecreases to 90 K. Before a sharp rise with a maximumjust below Tc, a small minimum was obtained. The originof this minimum just above Tc has not clear. Similar behav-ior has been previously obtained by many research groups[29,35,6971] and can be attributed to superconducting fluc-tuation contribution [35,46].

The origin of the maximum has also not been clarifiedfully. As mentioned in the first section, it can be either anelectronic contribution or caused by the reduction of thephonon scattering mechanism or both. However, in the re-cent studies, both on theoretical and experimental on thehigh-Tc materials, showed that the increase of just belowTc gives an evidence for enhancement of the quasiparticlecontribution to the heat conductivity and so an increase


of the quasi-particle mean free path [32,34,37,41,7278],where the main source of the quasi-particle scattering inthe high-Tc materials is electronic in origin.

In this work, the magnitude of was influenced by theEr concentration in the material. When the Er concentra-tion was increased the magnitude of was suppressed. Itstrongly indicates that the impurities play a significant rolein limiting the heat transport due to a strong increase of theelectronphonon-impurity scattering rate.

4. Conclusion

Structural formation, electrical resistance, thermoelec-tric power and thermal conductivity properties on theBi2Sr2Ca2Cu3xErxO10+ (x = 0.5 and 1.0) glassceramicsuperconducting system have been studied. XRD investi-gations showed that Er has a large effect on the unit cellparameters of the system. Both XRD and SEM-EDAXobservations indicate a solubility limit for Er ions in theBSCCO system.

High Er concentration promotes impurity phase forma-tion in the BSCCO system. We have also found that whenEr concentration increased in the Bi-2223 material, crystal-lization and also melting temperature increases significantly.Electrical resistance measurements showed a decrease onTc and Tzero values of the samples when the Er concentra-tion was increased and its effect on the S is similar for allsamples, it suggests that the substitution of Er changes thedistribution of charges between BiO and CuO planes andmore importantly it may be resulted in an increase in thehole concentration in the CuO plane.

The obtained data on the thermal conductivity measure-ments have shown a strong relation between the Er con-centrations. The maximum peak in Fig. 9 is shifted to thelower temperature with increasing Er concentration in thesystem. By considering the results from (T) measurements,our data seems to support the electronic contribution to thetotal thermal conductivity below Tc.

References

[1] R.K. Nkum, A. Punnett, W.R. Datars, Physica C 202 (1992) 371.[2] M. Ambai, Y. Yasui, J. Takeda, M. Sato, J. Phys. Chem. Solids 62

(2001) 187.[3] S. Bhattacharya, D.K. Modak, P.K. Pal, B.K. Chaudhuri, Matt. Chem.

Phys. 68 (2001) 239.[4] Z. zhanl, M.E. Yaknc, Y. Balc, M.A. Aksan, J. Supercond. 15

(2002) 543.[5] A.K. Ghosh, A.N. Basu, Supercond. Sci. Technol. 11 (1998) 852.[6] P.H. Duvigneaud, C. De Boeck, Y.F. Guo, Supercond. Sci. Technol.

11 (1998) 116.[7] A. Fujiwara, Y. Koike, K. Sasaki, M. Mochida, T. Noji, Y. Saito,

Physica C 208 (1993) 29.[8] H. Zhang, Y. Zhao, C.H. Cheng, Supercond. Sci. Technol. 12 (1999)

1163.

[9] M. Kato, W. Ito, Y. Koike, T. Noji, T. Saito, Physica C 226 (1994)243.

[10] S. Chatterjee, P.K. Pal, S. Bhattacharya, B.K. Chaudhuri, Phys. Rev.B 58 (1998) 12427.

[11] S. Bhattacharya, S. Chatterjee, K. Goswami, B.K. Chaudhuri, J.Mater. Sci. Lett. 17 (1998) 1575.

[12] A.E. Koshelev, V.M. Vinokur, Phys. Rev. B 57 (1998) 8026.[13] M.A. Aksan, Investigation of the Thermoelectric Power and Thermal

Conductivity Properties Together with the Physical Properties inBi-Based H-Tc Superconductors, Ph.D. Thesis, Graduate School ofNatural and Applied Sciences, Inonu University, 2003.

[14] R. Cloots, H. Bougrine, M. Houssa, S. Stassen, L. DUrzo, A.Rulmont, M. Ausloss, Physica C 231 (1994) 259.

[15] H.K. Barik, S. Bhattacharya, S. Chatterjee, P.K. Pal, B.K. Chaudhuri,Philos. Mag. B 79 (8) (1999) 1161.

[16] S. Chatterjee, B.K. Chaudhuri, T. Komatsu, Solid State Commun.104 (2) (1997) 67.

[17] S. Chatterjee, S. Banerjee, S. Mollah, B.K. Chaudhuri, Phys. Rev.B 53 (9) (1996) 5942.

[18] S. Dorbolo, M. Ausloos, H. Bougrine, B. Robertz, R. Cloots, J.Mucha, K. Durczewski, J. Supercond. 125 (5) (1999) 623.

[19] J.E. Rodriques, A. Marino, J. Giraldo, Physica C 282/287 (1997)1253.

[20] L. Forro, M. Raki, J.Y. Henry, C. Ayache, Solid State Commun. 69(1989) 1097.

[21] S. Ikegawa, T. Wada, T. Yamashita, A. Ichinose, K. Matsuura, K.Kubo, H. Yamauchi, S. Tanaka, Phys. Rev. B 43 (1991) 11508.

[22] V.E. Gasumyants, V.I. Kaidanov, E.V. Vladimirskaya, Physica C 248(1995) 255.

[23] Y. Xin, K.W. Wong, C.X. Fan, Z.Z. Sheng, F.T. Chan, Phys. Rev. B48 (1993) 557.

[24] S. Basak, S.K. Ghatak, Int. J. Mod. Phys. B 13 (1999) 1633.[25] L. Zhang, C. Liu, X. Yang, Q. Han, Physica B 279 (2000) 230.[26] C. Uher, W.N. Wang, Phys. Rev. B 40 (1989) 2694.[27] B. Chanda, T.K. Dey, Solid State Commun. 89 (1994) 353.[28] M.A. Aksan, M.E. Yakinci, Y. Balci, H. Ates, J. Low. Temp. Phys.

117 (1999) 957.[29] E. Natividad, M. Castro, R. Burriel, L.A. Angurel, J.C. Diez, R.

Navarro, Supercond. Sci. Technol. 15 (2002) 1022.[30] K. Knizek, M. Veverka, E. Hadova, J. Hejtmanek, D. Sedmidubsky,

E. Pollert, Physica C 302 (1998) 290.[31] M.E. Yaknc, J. Phys.: Condens. Matter 9 (1997) 1105.[32] M. Houssa, M. Ausloos, Phys. Rev. B 51 (1995) 9372.[33] S. Wermbter, L. Tewordt, Physica C 183 (1991) 365.[34] M. Houssa, M. Ausloos, Physica C 257 (1996) 321.[35] S. Castellazzi, M.R. Cimberle, C. Ferdeghini, E. Giannini, G. Grasso,

D. Marre, M. Putti, A.S. Siri, Physica C 273 (1997) 314.[36] P.M. Hui, X. Zhang, J. Markworth, D. Stroud, J. Mater. Sci. 34

(1999) 5497.[37] M. Houssa, M. Ausloos, S. Sergeenkov, J. Phys.: Condens. Phys. 8

(1996) 2043.[38] S.D. Peacor, R.A. Richardson, F. Nori, C. Uher, Phys. Rev. B 44

(1991) 9508.[39] L. Tewordt, T. Wolkhausen, Solid State Commun. 70 (1989) 839.[40] L. Tewordt, T. Wolkhausen, Solid State Commun. 75 (1990) 515.[41] R.C. Yu, M.B. Salamon, J.P. Lu, W.C. Lee, Phys. Rev. Lett. 69

(1992) 1431.[42] C. Uher, Physical Properties of HTSC, vol. 3, in: D.M. Ginsberg

(Ed.), World Scientific, Singapore, 1992.[43] A. Jezowski, J. Mucha, K. Rogaci, R. Horyn, Z. Bukovski, M.

Horobiowski, Phys. Lett. A 122 (1987) 431.[44] S.D. Peacor, J.L. Cohn, C. Uher, Phys. Rev. B 43 (1991) 8721.[45] D.T. Morelli, J. Heremans, D.E. Swets, Phys. Rev. B 36 (1987) 3917.[46] J.L. Cohn, E.F. Skelton, S.A. Wolf, J.Z. Liu, R.N. Shelton, Phys.

Rev. B 45 (1992) 13144.[47] C. Uher, A.B. Kaiser, Phys. Rev. B 36 (1987) 5680.


[48] T. Hirai, in: Processing of Ceramics, Part 2, in: R.J. Brook (Ed.),VCH Verlagsgesellschaft mbH, Weinheim, Germany, 1996, p. 293.

[49] J. Markworth, K.S. Ramesh, W.P. Parks Jr., J. Mater. Sci. 30 (1995)2183.

[50] J. Bardeen, G. Rickayzen, L. Tewordth, Phys. Rev. 133 (1959) 982.[51] M.A. Aksan, M.E. Yaknc, Y. Balc, Supercond. Sci. Technol. 13

(2000) 955.[52] T. Komatsu, R. Sato, K. Matusita, T. Yamashita, Appl. Phys. Lett.

54 (1989) 1169.[53] J.M. Tarascon, W.R. Mckinnon, P. Barboux, D.M. Hwang, B.G.

Bagley, L.H. Greene, G.W. Hull, Y. LePage, N. Staffel, M. Giroud,Phys. Rev. B 38 (1988) 8885.

[54] P.W. McMillan, Glass-Ceramics, Academic Press, London, 1979.[55] M.R. Presland, J.L. Tallon, R.G. Buckley, R.S. Liu, N.E. Floer,

Physica C 176 (1991) 95.[56] S.D. Obertelli, J.R. Cooper, J.L. Tallon, Phys. Rev. B 46 (1992)

14928.[57] D.R. Sita, R. Singh, Physica C 296 (1998) 21.[58] R. Wang, H. Sekine, H. Jin, Supercond. Sci. Technol. 9 (1996) 529.[59] R. Singh, D.R. Sita, Physica C 312 (1999) 289.[60] Z.W. Zhao, S.L. Li, H.H. Wen, X.G. Li, Physica C 391 (2003) 169.[61] L. Forro, J. Lukatela, B. Keszei, Solid State Commun. 73 (1990) 501.[62] V. Gottwick, K. Glass, F. Horn, F. Steglich, N. Grewe, J. Magn.

Magn. Mater. 4748 (1985) 536.[63] G.G. Qian, K.Q. Ruan, X.H. Chen, C.Y. Wang, Y.X. Wang, Q. Cao,

L.Z. Cao, H. Zhang, Y.Z. Ruan, Phys. Status Solidi (a) 168 (1998)267.

[64] G.G. Qian, K.Q. Ruan, X.H. Chen, C.Y. Wang, L.Z. Cao, M.R. Ji,Physica C 313 (1999) 58.

[65] V.P.S. Awana, V.N. Moorthy, A.V. Narlikar, Phys. Rev. B 49 (1994)6385.

[66] D.K.C. McDonald, Thermoelectricity: An Introduction to the Prin-ciples, Wiley, New York, 1962.

[67] V.P.S. Awana, S.B. Samanta, P.K. Dutta, E. Gmelin, A.V. Narlikar,J. Phys.: Condens. Matter 3 (1991) 8893.

[68] S.B. Samanta, P.K. Dutta, V.P.S. Awana, A.V. Narlikar, Eyrophys.Lett. 16 (1991) 391.

[69] F.G. Aliev, V.V. Moshalkov, V.V. Pryadun, M.A. Arranz Monge,Solid. State Commun. 82 (1992) 241.

[70] M. Ausloss, M. Houssa, J. Phys: Condens. Matter 6 (1994) 6305.[71] A.K. Dhami, T.K. Dey, J. Supercond. 13 (2000) 617.[72] M. Ausloss, M. Houssa, Supercond. Sci. Technol. 12 (1999)

R103.[73] F. Yu, M.B. Salaman, V. Kopylov, N.N. Kolesnikov, H.M. Duan,

A.M. Hermann, Physica C 235/240 (1994) 1489.[74] E. Schachinger, J.P. Carbotte, Phys. Rev. B 57 (1998) 13773.[75] T. Plackowski, A. Jezowski, Z. Bukowski, Z. Phys. B 104 (1997)

745.[76] T. Wolkhausen, Physica C 234 (1994) 57.[77] D. Livanov, G. Fridman, Nuovo Cimento D 16 (1994) 325.[78] B. Zeini, A. Freitmuth, B. Bchner, M. Galffy, R. Gross, A.P. Kampf,

M. Klaser, G. Mller-Vogt, L. Winkler, Eur. Phys. J. B 20 (2001)189.

Synthesis and characterization of Er-substituted Bi-2223 H-Tc glass-ceramic superconductorsIntroductionExperimentalResults and discussionX-ray diffraction investigationScanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX)Differential thermal analysis (DTA) investigationElectrical propertiesHole concentrationThermoelectric power (S)Two-band model with linear T-termXin' s two band model

Thermal conductivity kappa(T)

ConclusionReferences

(10,11)ceramic glass superconductors1 s2.0 s0925838804006863 main

Documents