Physica C 483 (2012) 94–96

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Physica C

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Superconducting and thermoelectric properties of new layered superconductorBi4O4S3

S.G. Tan a, L.J. Li a, Y. Liu a, P. Tong a, B.C. Zhao a, W.J. Lu a, Y.P. Sun a,b,⇑a Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of Chinab High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China

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

Article history:Received 3 August 2012Accepted 19 August 2012Available online 11 September 2012

Keywords:SuperconductivityType II-superconductorThermoelectric

0921-4534/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.physc.2012.08.003

⇑ Corresponding author at: Key Laboratory of MaterState Physics, Chinese Academy of Sciences, Hefei 2China. Tel.: +86 551 559 2757; fax: +86 551 559 143

E-mail address: ypsun@issp.ac.cn (Y.P. Sun).

Polycrystalline sample of the new layered superconductor Bi4O4S3 is successfully synthesized by solid-state reaction method by using Bi, S and Bi2O3 powders with one-step solid state reaction. The supercon-ducting transition temperature ðTonset

c ¼ 4:5 KÞ, the zero resistance transition temperature (Tc0 = 4.07 K)and the diamagnetic transition temperature (4.02 K at H = 10 Oe) were confirmed by electrical transportand magnetic measurements. Also, our results indicate a typical type II-superconductor behavior and thecharge carriers are mainly electron-type. In addition, a large thermoelectric effect was observed with adimensionless thermoelectric figure of merit (ZT) of about 0.03 at 300 K.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

To study the layered materials is one of the strategies forexploring new superconductors. The discoveries of superconduc-tivity with high superconducting transition temperatures in cup-rates [1–4] and oxypnictides [5–8] are good examples. Veryrecently, Mizuguchi et al. reported the superconductivity in lay-ered Bismuth-oxysulfide Bi4O4S3 [9] with Tc0 = 4.5 K. Just ten dayslater, Li et al. reported the measurements of resistivity, Hall effectand magnetization of Bi4O4S3 [10]. Their results indicate an exoticmulti-band behavior and show the feature of superconductingpairing in one dimensional chain. Structurally, Bi4O4S3 is composedof stacking of Bi4O4(SO4)1�x and Bi2S4 layers. The BiS2 layer is abasic unit as the Cu–O layer in Cu-based superconductors [1–4]and the Fe–An (An = P, As, Se, Te) layer in oxypnictides [5–8]. TheBi4O4S3 superconductor as a new member in the layered supercon-ducting family may stimulate further studies on the materials withBiS2 layer.

The reported preparations for Bi4O4S3 superconductor containtwo steps [9,10]. Firstly, the Bi2S3 polycrystalline powder shouldbe prepared using solid-state reaction by Bi powder and S grain.And then, the obtained Bi2S3 powder, Bi2O3 powder and S grainswere used to prepare Bi4O4S3 polycrystalline by solid-state reac-tion. Here, we report a one-step solid-state reaction method forthe superconducting Bi4O4S3. Our magnetization measurementindicates Bi4O4S3 is a typical type II-superconductor. Thermal

ll rights reserved.

ials Physics, Institute of Solid30031, People’s Republic of

4.

transport measurements show a large Seebeck coefficient withnegative values, indicating the dominant charge carriers are elec-tron-like.

2. Experimental

The Bi, S and Bi2O3 powders in stoichiometric ratio were fullymixed and ground, and then pressed into pellets. The pellets weresealed in an evacuated silica tube. The tube was heated for 10 h at510 �C. The obtained pellets were ground again and the abovetreatment was repeated. Finally, polycrystalline Bi4O4S3 were ob-tained. The room-temperature crystal structure and lattice con-stants were determined by powder X-ray diffraction (XRD)(Philips X’pert PRO) with Cu Ka radiation. The electronic andthermal transport measurements were performed in a QuantumDesign physical property measurement system (PPMS), and themagnetization measurement was performed on a superconductingquantum interference device (SQUID) system.

3. Results and discussion

Fig. 1 shows the XRD pattern for the Bi4O4S3 polycrystalline. TheBragg diffractions can be indexed using the tetragonal structurewith the space group of I4/mmm. The lattice parameters are ob-tained by fitting the powder XRD pattern by using the Rietica soft-ware [11], and the obtained lattice constants a, b and c area = b = 0.3978 nm, c = 4.107 nm, respectively, which are in consis-tence with the reported results [9].

Fig. 2 shows the temperature dependence of the resistivity ofthe Bi4O4S3 polycrystalline measured by a standard four-probe

Fig. 1. Rietveld refinement results of the XRD pattern at room temperature for theBi4O4S3 sample. Solid crosses indicate the experimental data and the calculated datais the continuous line overlapping them. The lowest curve is the difference betweenthe experimental and calculated patterns. The vertical bars indicate the Braggreflection positions. The Miller indices are also marked. Inset shows the crystalstructure of Bi4O4S3.

Fig. 2. Temperature dependence of the resistivity q(T) for Bi4O4S3. The inset showsthe low-temperature q(T) curve at different applied magnetic fields.

Fig. 3. Temperature dependence of the magnetic susceptibility of Bi4O4S3 at H = 10Oe. The top inset shows the magnetization hysteresis loop of Bi4O4S3 at T = 2 K. Theright bottom inset shows the initial M(H) isotherm at T = 2 K, the red dash lineshows the linear fitting in the low field range. (For interpretation of the referencesto color in this figure legend, the reader is referred to the web version of thisarticle.)

Fig. 4. Temperature dependence of the (a) thermal conductivity and resistivity, (b)Seebeck coefficient and ZT values for Bi4O4S3.

S.G. Tan et al. / Physica C 483 (2012) 94–96 95

method under a zero magnetic field. As seen from Fig. 2, the Bi4O4-

S3 has a metallic behavior in the normal state, and the magnitudeof the resistivity is slightly less than that reported in Ref. [9] in thewhole measurement temperature region. When the sample wascooled down to 5 K, the resistivity has an abrupt drop due to theoccurrence of superconductivity. The inset of Fig. 2 shows thelow temperature resistivity of Bi4O4S3 at different applied mag-netic field (H). The superconducting transition temperatureTonset

c

� �and zero resistivity temperature (Tc0) of the sample are

determined to be 4.5 K and 4.02 K at H = 0 T, respectively, andthe superconducting transition width is determined to be 0.3 Kaccording to 10–90% of the normal state resistivity, such a narrowwidth indicates the good homogeneity of the sample. Both Tonset

c

and Tc0 shift to lower temperatures with the increase of H.The superconductivity was also proved by the magnetic

measurements shown in Fig. 3. The diamagnetism in the low-temperature region further confirms the existence of superconduc-tivity, and the steep transition in the M(T) curve indicates that thesample is rather homogeneous. The superconducting diamagnetictransition begins at 4.02 K, defined by the onset point of the

zero-field-cooling (ZFC) and field-cooling (FC) curves. It is consis-tent with the Tc0 obtained from the resistance measurement. Thesmaller magnetization value for FC is likely due to the complicatedmagnetic flux pinning effects [12]. The value of �4pv at 2 K isabout 33%. The top inset of Fig. 3 shows the magnetization hyster-esis loop of Bi4O4S3 at T = 2 K. The shape of the M(H) curve indi-cates that Bi4O4S3 is a typical type-II superconductor. The bottominset of Fig. 3 shows the initial M(H) curves of the Bi4O4S3 in thelow-field region at 2 K, which allows us to estimate the lower crit-ical field values (Hc1) at 2 K. At low fields, the M(H) isotherm is lin-ear with H, as expected for a BCS type-II superconductor. Theestimated Hc1 (2 K) value is about 7.4 Oe, defined by the pointwhere the curve deviates from linearity (marked by the arrow inthe inset of Fig. 3).

The thermal transport measurement results which are contain-ing the Seebeck coefficient (S), electrical resistivity q, thermal

96 S.G. Tan et al. / Physica C 483 (2012) 94–96

conductivity j are shown in Fig. 4. The j(T) shows a broad peak ataround 25 K. The origin is unknown at present. The S(T) is negativein the whole measurement temperature region, indicating the ma-jor carriers are electron-like. It is in agreement with the Hall mea-surement results [10]. The S(T) is linearly dependent withtemperature when T is less than 50 K, above which the S(T) is lesstemperature dependent. It results in a broad slope change at�100 K. In the similar temperature region, a broad minimum inthe Hall coefficient RH(T) was observed [10]. It indicates the tem-perature dependence of S(T) is mainly governed by the evolutionof charge carrier density with temperature. The dimensionless fig-ure of merit, ZT (ZT = S2T/qj), which represents for the efficiency ofa thermoelectric material, was calculated and presented in Fig. 4b.Due to the low resistivity, and relatively small thermal conductiv-ity, the ZT value of our sample at 300 K reaches about 0.03. The ZTvalue at 300 K is comparable to the Fe-based superconductors LaF-ePO1�xFx and LaFeAsO1�xFx [13], while larger than cuprates HgBaC-aCuO (1223) and BiSrCaCuO (2212) [14] by a few magnitudes.

4. Conclusions

In summary, polycrystalline sample of the new layered super-conductor Bi4O4S3 was prepared by a one-step solid-state reactionmethod using Bi, S and Bi2O3 powders. The electronic and magneticmeasurements show that the onset transition temperature andzero resistance transition temperature are Tonset

c ¼ 4:5 K andTc0 = 4.02 K, respectively. Our data clarify that Bi4O4S3 is a typicaltype II-superconductor and the electron-type carriers are domi-nant. Further, the large thermoelectric effect was observed withZT = 0.03 at room temperature.

Acknowledgments

This work was supported by the National Key Basic Researchunder contract No. 2011CBA00111, and the National NatureScience Foundation of China under contract Nos. 11104279,11174293, 51102240, 11204314 and U1232139 and Director’sFund of Hefei Institutes of Physical Science, Chinese Academy ofSciences.

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