Physica C 470 (2010) 244–249

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Physica C

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Electrical and thermal properties of bulk superconductorsEu0.95Pr0.05Ba2(Cu1�xMx)3O7�d (M = Fe, Ni, Zn and Mn)

Tirthankar Chakraborty a, Bhasker Gahtori b, Ajay Soni c, G.S. Okram c, S.K. Agarwal b, Y.-S. Chen d,Y.-K. Kuo d,*, Geetha e, Ashok Rao e,*, Chandan Kumar Sarkar a

a Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700 032, Indiab Superconductivity and Cryogenics Division, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110 012, Indiac UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017, Indiad Department of Physics, National Dong-Hwa University, Hualien 974, Taiwane Department of Physics, Manipal Institute of Technology, Manipal 576 104, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 28 July 2009Received in revised form 29 December 2009Accepted 6 January 2010Available online 13 January 2010

Keywords:A. High TC superconductorsD. Critical fieldC. Transport propertiesD. Specific heat

0921-4534/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.physc.2010.01.011

* Corresponding authors. Tel./fax: +91 820 2571071E-mail addresses: ykkuo@mail.ndhu.edu.tw (Y.-K.

mail.com (A. Rao).

Measurements of transition temperature, magneto-resistance, thermal conductivity, thermo-electricpower and specific heat have been carried out on co-doped samples of Eu0.95Pr0.05Ba2(Cu1�xMx)3O7�d

(M = Fe, Ni, Zn and Mn) compounds. It is found that all samples exhibit metallic behavior, except theco-doped sample of Fe that shows semiconducting behavior. It is seen that the upper-critical field Hc2

decreases with Pr-doping. However, an increase in Hc2 for dopants like Fe and Mn is observed. Thermalconductivity for the pristine sample of EuBa2Cu3O7�d (Eu-123) exhibits a pronounced hump below thesuperconducting transition temperature TC. However, the peak height of the hump decreases with Pr-doping and such a feature is further suppressed in the co-doped samples. The negative sign of the mea-sured thermo-electric power of Eu-123 indicates that the dominant carrier in this sample is electron-like,whereas it turns to hole-like for all of the doped samples. A jump in specific heat CP is detected in the puresample of Eu-123 at TC, while only a change in slope in CP is seen around the transition temperature in thePr-doped sample.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

Effects of Pr substitution have been extensively studied in RE-Ba2Cu3O7�d (RE = rare-earth elements) cuprates [1–9] and suchstudies are useful to understand the mechanism of superconduc-tivity. It is seen that Pr-doping quenches superconductivity and ametal–insulator transition occurs. It is further seen that the mostprominent effect induced by Pr is an enlargement of the distancebetween the CuO2 layers. The valency of Pr has also been subjectof interest and there have been several controversies regardingthe same [10–14]. It is observed that the suppression of transitiontemperature, TC, does not follow the Abrikosov–Gor’kov theory[15]. Another important feature of Pr is its magnetic ordering tem-perature TN = 17 K [16], which is higher than that seen inGdBa2Cu3O7�d system (TN = 2 K) [17]. Among these Pr substitutionstudies, most of them are limited to systems with RE = Y and Gd. Itshould be pointed out that the Pr ion is more effective in suppress-ing TC when the RE ion has a large ion radius. It is thus expected

ll rights reserved.

(A. Rao).Kuo), ashokanu_rao@rediff-

that the suppression of TC would be stronger in the cases of Euand Nd-based systems. However, little work in the literature seemsto have been done on the Eu1�xPrxBa2Cu3O7�d system [7,18–21].

During the last decade or so, many studies have suggested thatcompared to YBa2Cu3O7�d system, other RE based systems have abetter applicability [22–29]. In particular, Eu-based system is ofgreat importance for thin film technologies as such a system showsbetter surface morphology and exhibits higher transition tempera-tures [22,29]. Recently we had reported electrical and thermaltransport properties of pure and Mn-doped EuBa2Cu3O7�d system[30]. This motivated us to prepare pure and co-doped compoundsof EuPrBaCuMO (where M is a transition metal) system and carryout studies on electrical and thermal transport properties. Studyof transport properties has been a source of information not onlyfor understanding the theoretical aspects, but also for their techno-logical applications. In this communication we have limited oursystem by preparing samples with 5% Pr along with low concentra-tions of Fe, Mn, Zn and Ni. We have chosen two types of systemsviz. Fe, Mn; and Ni, Zn, which occupy Cu(I) and Cu(II) sites, respec-tively. The main advantage of low content of transition metals isthat disorder may not be the dominating effect of impurity, ratherthe dominating effect may be ‘‘electronic effect” [31].

20 30 40 50 60 70 800

1000

2000

3000

4000

5000 Eu0.95

Pr0.05

Ba2(Cu

1-xM

x)

3O

7-δ

(091)(300)(081)(161)

(002)(060)(131)

(050)

(031)(130)

(030) x= 0.02 (M= Ni)

x= 0.02 (M= Zn)

x= 0.02 (M= Fe)

x= 0.02 (M= Mn)

x= 0.00

EuBa2Cu3O7-δ

Inte

nsit

y (a

rb.u

nit)

2θ (Degree)

Fig. 1. X-ray diffraction pattern of Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d samples withvarious M.

50 100 150 200 250 3000

1

2

3

4

5

6Eu

0.95Pr

0.05Ba

2(Cu

1-xM

x)

3O

7-δR

esis

tivi

ty (

mΩ

-cm

)

Temperature (K)

EuBa2Cu3O7-δ x= 0.00 x=0.02 (M= Mn) x= 0.02 (M= Ni) x= 0.02 (M= Fe) x= 0.02 (M= Zn)

Fig. 2. Resistivity versus temperature plots of pure EuBa2Cu3O7�d andEu0.95Pr0.05Ba2Cu2.94M0.06O7�d samples for various M.

T. Chakraborty et al. / Physica C 470 (2010) 244–249 245

2. Experimental details

Samples of Eu0.95Pr0.05Ba2(Cu1�xMx)3O7�d system in the nominaldoping range 0 6 x 6 0.02 were prepared by standard solid statereaction technique described elsewhere [32]. The structural andphase analysis of the samples was performed using an X-ray dif-fractometer. In the present investigation, X-ray diffraction data(XRD) were collected at room temperature from 20� to 80� witha 2h step of 0.05� using an Rigaku Mini-Flex II desktop X-ray dif-fractometer with CuKa1 (k = 1.5405 Å) radiation as a source. Thelattice parameters are given in Table 1. The XRD patterns for thesamples in the present investigation are shown in Fig. 1. TheXRD patterns indicate the presence of some impurity peaks likethat of BaCuO2. Temperature dependent electrical resistivity q(T)measurements at various magnetic fields have been carried outby the standard four-probe method. Thermal conductivity j(T)measurements were performed in a close-cycle refrigerator, usinga direct-pulse technique. The samples were cut to rectangular barsof dimensions 1.5 � 1.5 � 5.0 (mm3). One end of the sample wasmounted on a copper block, which served as a heat sink. A verysmall calibrated chip resistor was set at the other end of the sam-ple as a heat source. The temperature gradient was measured by anE-type differential thermocouple fixed directly on the sample facesand that was electrically insulated from the sample. To minimizethe heat radiation the temperature difference was controlled toless than 1 K. Thermo-electric power (S) measurement, in the tem-perature range of 5–300 K, was performed with a commerciallyavailable Dewar using the differential dc method, taking OFHC(oxygen-free highly conducting copper) as reference. The detailsare described elsewhere [33]. Specific heat measurements werecarried out using high resolution ac calorimeter, using choppedlight as a heat source. The details of the measurement techniqueare described elsewhere [32].

3. Results and discussion

3.1. Transition temperature and magneto-resistance

The temperature dependent resistivity is depicted in Fig. 2. Allthe samples, except the co-doped sample of Fe, show metallicbehavior. In contrast, the co-doped sample of Fe shows semicon-ducting behavior. We have observed that with Pr-doping the tran-sition temperature (TC) decreases while the transition width (DTC)increases in the Eu0.95Pr0.05Ba2Cu3O7�d (Eu–Pr5%) sample. Transi-tion temperatures of all the samples under present investigationsare given in Table 1. In the present studies, we have defined thetransition temperature as the one at which the resistivity becomeszero. With co-doping there is a further decrease in TC and an in-crease in DTC that are observed. It can be seen from the table thatthe depression in TC is maximum in case of co-doped samples of Znand least in Mn-doping. The values of TC and DTC of pure and Pr-doped samples are in good agreement with that reported in the lit-erature [7,18,19]. To the best of our knowledge, no studies havebeen done on co-doped samples of Eu–Pr. It may be pointed outthat, in the present studies, we have not done measurement of oxy-

Table 1Values of transition temperature (TC), upper-critical field [Hc2(0)] and lattice parameters ‘‘

Samples TC (K) Hc2(0) (T) a Parame

EuBa2Cu3O7�d 91.4 55.4 3.836Eu0.95Pr0.05Ba2Cu3O7�d 85.0 40.1 3.846Eu0.95Pr0.05Ba2Cu2.94Mn0.06O7�d 64.2 58.2 3.843Eu0.95Pr0.05Ba2Cu2.94Fe0.06O7�d 55.8 72.0 3.857Eu0.95Pr0.05Ba2Cu2.94Ni0.06O7�d 51.0 55.5 3.863Eu0.95Pr0.05Ba2Cu2.94Zn0.06O7�d 45.0 46.0 3.855

gen content of the samples, however, comparing the results withliterature we estimate the oxygen content of the samples around6.96.

Magneto-resistance measurements were performed on all sam-ples in the field range of 0–8 T. Fig. 3 shows a typical temperaturedependent resistivity data for two samples. It is observed that thetransition width increases with applied magnetic field. It is furtherseen that with the change in value of the magnetic field, the on-settransition temperature is almost constant. The change in normalstate resistivity is also very small with the magnetic field, however

a”, ‘‘b” and ‘‘c” for the samples Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d with various M.

ter [±0.001 Å] b Parameter [±0.001 Å] c Parameter [±0.001 Å]

3.882 11.6703.901 11.6843.904 11.6753.884 11.6563.887 11.7123.907 11.708

0 50 100 150 200 250 3000

1

2

3

4

60 80 1000

1

2

3

Eu Pr Ba Cu O

Res

isti

vity

(m

Ω-c

m)

Temperature(K)

(a)

(b)

Eu0.95

Pr0.05

Ba2Cu

3O

7-δ

Res

isti

vity

(mΩ

-cm

)

Temperature (K)

0T 1T 2T 4T 6T 8T

0 50 100 150 200 250 3000

2

4

6

0 25 50 75 1000

2

4

6Eu Pr Ba Cu Fe O

Res

isti

vity

(m

Ω-c

m)

Temperature(K)

Eu0.95

Pr0.05

Ba2Cu

2.94Fe

0.06O

7-δ

Res

isti

vity

(m

Ω-c

m)

Temperature (K)

0T 1T 2T 4T 6T 8T

Fig. 3. Resistivity versus temperature plots of the samples: (a)Eu0.95Pr0.05Ba2Cu3O7�d and (b) Eu0.95Pr0.05Ba2Cu2.94Fe0.06O7�d for various fields.The inset shows the temperature dependent variation of resistivity in the vicinity ofthe transition temperature.

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

5

4

6

3

2

1Eu

0.95Pr

0.05Ba

2(Cu

1-xM

x)

3O

7-δ

κ (m

W/c

mK

)

Temperature (K)

1. Eu-1232. EuPr-5%3. M= Mn4. M= Zn5. M= Fe6. M= Ni

Fig. 4. Variation of thermal conductivity (j) of the Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d

samples for various M in the temperature range 10–300 K.

246 T. Chakraborty et al. / Physica C 470 (2010) 244–249

in the mixed state; resistivity varies considerably with appliedmagnetic field. This is due to the fact that thermally activated fluxcreep and flux flow are responsible for such a behavior [9].

We have used the extrapolation procedure for estimating theupper-critical field (Hc2) and the obtained values of Hc2 for thestudied samples are listed in Table 1. For the pure sample of Eu-123 we estimated the value of upper-critical field of about 55 T.With Pr-doping it decreases to about 40 T. With the introductionof co-doping, we could see that the value of Hc2 increases for sam-ples of Fe and Mn. On the contrary, Hc2 decreases for sample of Zn,whereas for Ni-doped sample there is hardly any change in Hc2.

Table 2Values of the parameters B, a, b, g, hD and U according to the fitting equation with thethermal conductivity of Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d for various M. Here B, a, b, gand U are expressed in cm K/mW and hD is expressed in K.

Sample B a b g hD U

EuBa2Cu3O7�d 0.21 100.2 5.0 6.72 379 9.8Eu0.95Pr0.05Ba2Cu3O7�d 0.24 72.8 4.1 6.75 480 10.2Eu0.95Pr0.05Ba2Cu2.94Mn0.06O7�d 0.45 74.5 6.7 8.29 488 6.8Eu0.95Pr0.05Ba2Cu2.94Zn0.06O7�d 0.72 51.4 10.0 12.22 493 7.4Eu0.95Pr0.05Ba2Cu2.94Fe0.06O7�d 0.53 67.2 7.4 9.75 491 7.2Eu0.95Pr0.05Ba2Cu2.94Ni0.06O7�d 0.84 42.8 10.8 14.80 494 7.8

3.2. Thermal conductivity

Fig. 4 shows the temperature dependence of thermal conductiv-ity, j(T), for all studied samples. It is observed that in the normalstate, temperature dependence of thermal conductivity is almostlinear. It is further seen that for the Eu-123 and Eu–Pr5% samples,there is a hump like structure below their respective transitiontemperatures. Such a feature is commonly seen in superconductingcuprates and is attributed to the electron–phonon interaction asper the lattice theory of thermal conductivity [34]. In addition tothe electron–phonon scenario, the increase in j is an indication

for the enhancement of the quasi-particle contribution to the heatconduction and hence an increase of quasi-mean free path in thesehigh TC superconductors [35]. Thus we argue that there could be analternate possibility for the observed thermal conductivity humpwhich is essentially an electronic effect. With co-doping, the humpin j is only seen in Mn-doped compound. On the contrary, forother dopants like Fe, Ni and Zn no such a feature could be ob-served. We will now analyze the hump structure by determiningthe peak value of thermal conductivity which is denoted by jpeak.The value of jpeak for the pure sample is 66.3 mW/cm K whereaswith 5% Pr-doping it decreases drastically to 40.8 mW/cm K. Inco-doped sample of Mn, the peak value further decreases to35.2 mW/cm K and we could not get any hump in other co-dopedsamples. We have used the standard lattice model for determina-tion of the theoretical expression for thermal conductivity[36,37]. In the above mentioned model, we usually determine var-ious parameters B, a, b, g, U and hD. The parameters B, a, b, g and Urepresent scattering rate of phonons, respectively, with the bound-ary, point defects, sheet-like faults, electrons, and phonons. hD rep-resents the Debye temperature and these parameters for thepresently investigated samples are given in Table 2.

It is satisfactory to note that the experimentally observed valuesof thermal conductivity for pristine as well as co-doped samplesmatch fairly well with that obtained theoretically, as depicted inFig. 5. In fact one can see that the fit is nearly perfect for the puresample. With co-doping the theoretical curve matches well belowthe hump structure, however, with increase in temperature be-yond the hump, the theoretical curve is slightly below the experi-mental data. We now discuss the role of Pr and the other dopantsin the thermal transport property of the Eu-123 system. Theparameter B (boundary scattering) slightly increases with Pr-dop-

0 20 40 60 80 100 120 140

10

20

30

40

50

60

70κ

(mW

/cm

K)

Temperature (K)

EuBa2Cu

3O7-δ

Eu0.95

Pr0.05

Ba2Cu

3O7-δ

Eu0.95

Pr0.05

Ba2Cu

2.94Mn

0.06O7-δ

Fig. 5. Variation of j in the vicinity of superconducting transition. Points denote theexperimental results and curves depict the fitting results.

0 50 100 150 200 250 300

-5

0

5

10

15

20

25

30

63

5

2

4

1

Eu0.95

Pr0.05

Ba2(Cu

1-xM

x)

3O

7-δ

S (μ

V/K

)

Temperature (K)

1. EuBa2Cu

3O

7-δ2. x= 0.003. x= 0.02 (M= Mn)4. x= 0.02 (M= Zn)5. x= 0.02 (M= Fe)6. x= 0.02 (M= Ni)

Fig. 6. Variation of thermo-electric power (S) of the Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d

samples for various M with the temperature up to 300 K.

T. Chakraborty et al. / Physica C 470 (2010) 244–249 247

ing; however with co-doping there is a huge increase in B for all thedopants. This means that Pr-doping has little effect on boundaryscattering; on contrary, co-doping increases the boundary scatter-ing to the extent of 115–300%. We now see the effect of doping ona (point defect scattering). It is observed that with Pr-doping, a de-creases by about 28% and with co-doping there is further decreasesin a which ranges from 25% to 58%. This indicates that Pr-doping aswell as co-doping decreases scattering of phonons with point de-fects. We now see the effect of doping on the sheet-like faultswhich are represented by b. It is seen that b decreases with Pr-dop-ing but increases with co-doping. We notice that for dopants (Mnand Fe) which occupy Cu-I sites the sheet-like faults increase toabout 50%. On the other hand, with dopants (Zn and Ni) which oc-cupy Cu-II sites there is almost 100% enhancements in b. A similartrend in the electron–phonon interaction term g as that found in bin the co-doped samples is noted, while g remains almost un-changed with Pr-doping. Finally, it is seen that the phonon–phononscattering term U is relatively less affected by doping. Such a resultis expected since the phonon spectrum of these samples should notbe severely changed with such a low level of doping.

We now compare the present results with that in literature.Since no thermal conductivity measurements have been done onco-doped systems, hence we compare the present work with ourprevious work on Mn-doped samples of EuBa2(Cu1�xMnx)3O7�d

[30]. We observe that the fitting parameter a for 2% Mn co-dopedsample drastically decreases by a factor of 6, on contrary a decreasein a of about 2.2 is seen for the 2% Mn-doped sample of Ref. [30].However the behavior of the fitting parameters b and g for dopedand co-doped samples of Mn are not drastically different.

Table 3Values of l, Wr and l/Wr for the samples Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d with variousM.

Sample l (meV) Wr (meV) l/Wr

EuBa2Cu3O7�d 0.8 52.0 0.015Eu0.95Pr0.05Ba2Cu3O7�d 2.5 78.2 0.032Eu0.95Pr0.05Ba2Cu2.94Mn0.06O7�d 2.9 74.6 0.039Eu0.95Pr0.05Ba2Cu2.94Zn0.06O7�d 2.6 82.6 0.031Eu0.95Pr0.05Ba2Cu2.94Fe0.06O7-d 2.1 80.8 0.026Eu0.95Pr0.05Ba2Cu2.94Ni0.06O7�d 1.5 76.2 0.020

3.3. Thermo-electric power

Fig. 6 shows the temperature dependent thermo-electric power,S(T), for all the samples under present investigation. It is found thatthe pure sample shows electron-like behavior, whereas all otherco-doped samples exhibit hole-like behavior. In fact room temper-ature thermo-electric power is considered as a universal measureof various doping, and it is seen that co-doping changes the natureof charge carriers. Since there are no reports on thermo-electricpower measurements on co-doped system, hence we will compareour results with other doped cuprate superconductors. In particu-lar, present results are qualitatively similar to that observed fordoped samples of EuBa2(Cu1�xMnx)3O7�d [30].

In order to analyze the temperature dependence of thermo-electric power, we have used the theoretical model as proposedby Gasumyants et al. [38] which is based on a narrow band pictureof cuprates. In this model, one usually defines three parameters n,WD and Wr which respectively denote band filling, total effectiveband-width of the electronic states and effective width of an en-ergy interval for electron conduction. As in the present investiga-tion we have limited the temperature range to 300 K, we haveused only two parameters. The details of this model are describedin our earlier communication [34]. Using the narrow-band model,we have fitted the experimental curves and thus we have calcu-lated the chemical potential l and the parameter Wr and the ob-tained parameters are given in Table 3. We have also presentedl/Wr in Table 3. Fig. 7 shows the comparison of the experimentaldata with that obtained by the theoretical model and a satisfactoryagreement between the fits and measured data can be clearly seen.

We now investigate the effect of doping on the parameters land Wr. We note that the chemical potential, l, drastically in-creases with Pr-doping. However, with co-doping the chemical po-tential decreases. We see that the parameter Wr increases with Pr-doping and there is nominal effect on Wr with further transitionmetal doping. In the above mention two-parameter model, the ra-tio of l/Wr plays an important role as it signifies the strength ofthe carrier scattering rate. One can see that Pr-doping introducesweak scattering processes, whereas co-doping introduces strongscattering. A possible reason for this effect may be due to the factthat Pr-doping produces mainly electronic effects, i.e., the changeof carrier density and transfer of spectral weight from high energyregime to low energy regime [39]. With co-doping these electroniceffects become weaker while the carrier scattering processes be-come stronger.

20 40 60 80 100 120 140-10

0

10

20

30

S (μ

V/K

)

Temperature (K)

EuBa Cu OEu Pr Ba Cu OEu Pr Ba Cu Mn O

Fig. 7. Behavior of thermo-electric power (S) of the Eu0.95Pr0.05Ba2Cu2.94M0.06O7�d

samples for various M in the temperature range 45–140 K. Points denote exper-imental results and curves depict the fitting.

100 150 200 250 300

150

200

250

300

350

400(b)

70 80 90 100 1101.85

1.90

1.95

2.00

2.05

TC

Cp/T

(m

J/gK

2 )

Temperature (K)

Eu0.95

Pr0.05

Ba2Cu

3O

7-δ

Cp(m

J/gK

)

Temperature (K)

150

200

250

300

350

400

80 85 90 95 100 105

2.00

2.05

2.10

TC

Cp/T

(m

J/gK

2 )

Temperature (K)

EuBa2Cu

3O

7-δ

Temperature (K)100 150 200 250 300

Cp(m

J/gK

)

(a)

Fig. 8. The temperature dependence of specific heat of: (a) EuBa2Cu3O7�d and (b)Eu0.95Pr0.05Ba2Cu3O7�d sample. The inset shows temperature dependent variationsof CP/T in the vicinity of the transition temperature.

248 T. Chakraborty et al. / Physica C 470 (2010) 244–249

3.4. Specific heat

In Fig. 8a the temperature dependent specific heat, CP(T), of thepristine sample Eu-123 is shown. We have presented the specificheat data in the vicinity of the transition temperature as an insetof Fig. 8a. Here in the inset we have plotted CP/T as a function oftemperature as jumps in CP are best seen in such plots. The presentresults of specific heat do not show a sharp discontinuity aroundthe transition temperature. Instead CP increases gradually as thesample under goes the transition from normal to superconductingstate. In contrast, conventional superconductors exhibit sharp dis-continuity in specific heat. This difference is fundamentally due tothe broad transition widths (2–3 K) in high TC superconductors indisparity with the sharp transition width (about 1 mK) in conven-tional superconductors.

The jump of specific heat at TC was determined by extrapolatingthe two branches of CP/T versus T curves at TC. For the pristine sam-ple we observed a jump in specific heat of about 1.46 J/mol K. Thisis in good agreement with those observed by Rao et al. [30] andPlackowski et al. [40]. Fig. 8b shows the temperature dependentspecific heat of Eu0.95Pr0.05Ba2Cu3O7�d sample. In the inset ofFig. 8b we have shown CP/T in the vicinity of transition tempera-ture. For this sample we could not observe a jump in specific heatat the transition temperature, instead a change in slope was seen atTC. This behavior of a change from a ‘clear peak’ to ‘change in slope’in CP suggests that Pr is either inducing gapless superconductivityor there exists strong thermal fluctuations near TC.

4. Conclusion

In this work, the effects of co-doping on the thermal and electri-cal transport properties were investigated. All the samples (exceptco-doped sample of Fe) exhibit metallic behavior. It is also seenfrom magneto-resistance measurements that the upper-criticalfield Hc2(0) decreases for the Pr-doped and Zn co-doped samples.However for co-doped samples of Fe and Mn, the upper-criticalfield increases. It is found that the thermal conductivity of the pris-tine sample and Pr-doped sample there is a hump like structure be-low their respective transition temperatures, whereas such afeature is strongly suppressed in the co-doped samples. A theoret-ical attempt to model the T-dependent j reveals that Pr-doping hasa minor effect on the heat conduction mechanism. However, co-doping with transition metal in the Eu-123 system causes a sub-stantial increase in boundary scattering, sheet-like fault scattering,and electron–phonon scattering. Thermo-electric power measure-ments indicate that the pristine sample shows an electron-likebehavior. However, the charge carriers change from electron-liketo hole-like with Pr and co-doping. By analyzing the measuredS(T) with the narrow-band model, it is suggested that Pr-doping in-duces weak carrier scattering processes, while co-doping intro-duces strong carrier scattering. A jump in specific heat isobserved only for the pristine sample; with Pr-doping this jumpchanges to a slope change and no anomalous feature in CP couldbe detected in the co-doped samples.

Acknowledgements

One of us (T.C.) is grateful to UGC-DAE Consortium for ScientificResearch, Indore for financial support under the scheme CSR In-dore/PROJ/SANC/13/2006/1429. The authors are thankful to Mr.Sachin Kumar, UGC-DAE CSR, Indore for providing the necessaryhelp in magneto-resistance measurements. The experimental workis supported by the National Science Council of Taiwan under Con-tracts No. NSC-97-2628-M-259-001-MY3 (Y.K.K.).

T. Chakraborty et al. / Physica C 470 (2010) 244–249 249

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