J Supercond Nov Magn (2015) 28:459–467DOI 10.1007/s10948-014-2725-7

ORIGINAL PAPER

Synthesis, Structure, and Properties of the SuperconductorBa1−xKzBi1−yPbyO3

Hao Zhang · Xiaohuan Lin · Yuntian Zheng ·Shuang-er Li · Guobao Li · Fuhui Liao · Jianhua Lin

Received: 7 June 2014 / Accepted: 18 August 2014 / Published online: 3 September 2014© Springer Science+Business Media New York 2014

Abstract The series of BaBi1−yPbyO3(0 ≤ y ≤1) hasbeen synthesized by high-temperature solid-state reaction.X-ray and selected area electron diffraction data indicatethat BaBi1−yPbyO3(0 ≤ y ≤ 0.88) crystallizes in spacegroup P1 and BaBi1−yPbyO3 (0.93 ≤ y ≤1) crystallizes inspace group Imma. The samples with the nominal formulaBaBi1−yPbyO3(y = 0.70, 0.80, 0.90) shows superconduc-tivity with transition temperature (Tc) around 11 K. WhenBaBi1−yPbyO3 (0 ≤ y ≤0.80) was treated with KOH andKF at 450◦C, the corresponding samples with the nomi-nal formula Ba1−xKzBi1−yPbyO3 (0 ≤ y ≤ 0.80) wereobtained, which shows superconductivity withTc changingfrom 30 to 11 K.

Keywords Superconductivity · Perovskite · BaBiO3 ·Tructure · Opotactic reaction

1 Introduction

Ba1−xKxBiO3 (BKBO) is a very interesting superconductorwith transition temperature (Tc) about 30 K because it hasthree-dimensional ABO3 perovskite structure and no tran-sition metal elements. [1] The atoms at the A site (such as

H. Zhang · X. Lin · G. Li (�) · F. Liao · J. Lin (�)Beijing National Laboratory for Molecular Sciences,State Key Laboratory of Rare Earth Materials Chemistryand Applications, College of Chemistry and MolecularEngineering, Peking University Beijing 100871,People’s Republic of Chinae-mail: liguobao@pku.edu.cne-mail: jhlin@pku.edu.cn

Y. Zheng · S. LiBeijing National Day School, Beijing 100039,People’s Republic of China

Ba and K) and the B site (such as Bi) in BKBO can bechanged by other elements to form a serials of superconduc-tors, e. g., Sr1−xKxBiO3 (x = 0.45–0.60, Tc .≈ 12 K) [2],Sr1−xRbxBiO3 (x . ≈ 0.50, Tc .≈ 13 K) [2], BaBi1−xPbxO3

(x = 0.05–0.30, Tc .≈ 13 K) [3], BaPb1−xSbxO3 (x .≈ 0.25,Tc .≈ 3.5 K) [4], (K0.87Bi0.13)BiO3(Tc . ≈ 3.5 K) [5],Ba0.9K0.1Pb0.75Bi0.25O3 (Tc .≈ 3.5 K). [6] Most of themare single-site (A or B)-doped BaBiO3. Double-site (bothA and B) doping BaBiO3-based superconductors are rare.Here, our tries to synthesize Ba1−xKxBi1−yPbyO3 are pre-sented. Some new superconductors with Tc around 20 Kwere found.

2 Experiment

The samples with the nominal formula BaBi1−y

PbyO3(y = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9,and 1.0, noted as BBP1, BBP2, ..., BBP11) were synthe-sized by solid-state reactions at the temperature between800 and 900◦C using BaCO3 (A.R.), Bi2O3(A.R.), andPbO2(A.R.) as raw materials in a process similar to syn-thesize BaBi1−xTaxO3 (0 .≤ x .≤ 0.5) reported previously.[7] The obtained BBP1 to BBP11 were mixed with KOHand KF with a ratio of BaBi1−yPbyO3:KOH:KF = 1:4:2by weight. The mixtures were then treated at 450◦C for 4 hand cooled to room temperature at 60◦ C/h. The cooledmixtures were washed with water and dried at 80◦ C. Thecorresponding samples were noted as BBP1K, BBP2K, ...,BBP11K, respectively.

Powder X-ray diffraction (PXRD) data of the sampleswere first collected for checking the phases of the sampleson a Rigaku D/Max-2000 diffractometer using a rotatinganode (CuKα, 40 kV and 100 mA), a graphite monochrom-eter and a scintillation detector. After that, the PXRD data

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Fig. 1 X-ray diffraction patterns of BaBi1−yPbyO3 (y = 0, 0.1, ...,1.0, noted as BBP1, BBP2, ..., BBP11, respectively)

of the samples for Rietveld refinement using GSAS [8, 9]were collected on a PANalytical Empyrean diffractometerwith CuKα1 radiation (1.540598 A). The existence of Ba,K, Bi, Pb, and F in the obtained samples were checkedby EDS performed on high-resolution electron microscropyJEM2100F. The selected area electron diffraction of the

samples were obtained also from JEM2100F with an accel-erating voltage of 200 KV. Magnetic susceptibility wasmeasured in the temperature range between 5 and 50 Kby SQUID magnetometer (Quantum Design MPMS) in anapplied magnetic field of 100 Oe. Resistance of selectedsample was measured between 2 and 50 K by physicalproperty measurement system (PPMS).

3 Results and Discussion

3.1 Crystal Structure and Superconductivityof BaBi1−yPbyO3(0.0 ≤ y ≤ 1.0)

The X-ray diffraction patterns of the samples BBP1 toBBP11 are similar to each other as shown in Fig. 1, indi-cating that they may have the similar structure. In ourprevious work [7], many efforts have been performed toconfirm that BaBiO3 crystallizes in space group P1 at roomtemperature with a = 6.141(1) A, b = 6.186 (1) A,c = 6.144 (1) A, α = 59.90 (1)◦ , β = 59.98 (1)◦,γ = 59.87 (1)◦ . The similarity of the X-ray diffractionpatterns of BaBi1−yPbyO3(0.0 .≤ y ≤ 1.0) induces that all

Fig. 2 SAED patterns along different directions (a–e) and the Rietveld plot of X-ray diffraction data (f) of BBP11

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Table 1 Rietveld refinement details for BBP11 and BBP10

BBP11 BBP10

Phase Aa Phase B

Lattice parameter a = 6.0285 (3) A, b = 8.5110 (3) A, a = 6.0417 (3) A, b = 8.5293 (3) A, a = 6.0367 (3) A, b = 6.0526 (3) A

c = 6.06523 (3) A c = 6.06867 (3) A c = 6.0560 (3) A, α = 59.76 (2)

β = 60.16 (2) , γ = 60.13 (2)◦

Space Group Imma Imma P1

Ba1 0.0000, 0.2500, 0.5028 (3) 0.0000, 0.2500, 0.5017 (3) 0.2503 (3), 0.2479 (3), 0.2670 (3)

Ba2 0.7496 (3), 0.7458 (3), 0.7682 (3)

Pb/Bib 0.0000, 0.0000, 0.0000 0.0000, 0.0000, 0.0000 0.0000, 0.0000, 0.0000

Pb/Bib 0.4995 (3), 0.5018 (3), 0.4986 (3)

O1 0.0000, 0.2500, 0.0532 (3) 0.0000, 0.2500, 0.0546 (3) 0.3505 (3), 0.1532 (3), 0.6732 (3)

O2 0.2500, −0.0293 (3), 0.2500 0.2500, −0.0499 (3), 0.2500 0.8041 (3), 0.7332 (3), 0.2402 (3)

O3 0.7675 (3), 0.2560 (3), 0.2326 (3)

O4 0.2522 (3), 0.8125 (3), 0.6864 (3)

O5 0.1922 (3), 0.7578 (3), 0.2513 (3)

O6 0.6807 (3), 0.2545 (3), 0.7639 (3)

R factorc Rwp = 0.092, Rp = 0.057 Rwp = 0.087, Rp = 0.056

aThe ratio of phase A:phase B is 0.81:1.00bThe ratio of Pb/Bi in phases A and B is about 0.925 and 0.880, respectivelycRn1

wp, Rn1p are the R factors of the whole patterns and the peaks only, respectively

of them may crystallize in space group P1. However, thespace groups reported for BaBi1−yPbyO3(0.0≤ y ≤1.0)[10,12–15] are different from P1 except BaBiO3. Therefore,careful checking was performed and the results were pre-sented below.

BaPbO3 (BBP11) has been reported to crystal-lize at room temperature in several different spacegroups: Pnma (a ≈ 6.023, b≈ 8.504, c ≈6.062 A)[18, 19],

Imma (a≈ 6.030, b≈ 8.509, c≈ 6.069 A) [20–22], andI2/m (a≈ 6.023, b≈ 8.504, c≈ 6.062 A, β ≈ 90.0.◦) [16,17]. The previous discussion on the structure of BaPbO3

is mainly based on the X-ray and neutron diffraction. As

proved, the selected area electron diffraction (SAED) isvery useful to help the determination of the structure ofa compound [7, 23, 24], which will show the diffractionconditions to help the choice of the corresponding spacegroups. Then the SAED patterns of BBP11 were obtainedand shown in Fig. 2. The following diffraction conditionscan be obtained: hkl, h+k+l=2n; hk0, h= 2n and k= 2nwith a ≈ 6.023, b ≈ 8.504, c≈ 6.062 A, α ≈ β ≈γ ≈ 90.0.◦ . These diffraction conditions correspond tothe space group Imma and its subgroups: Im2b, I112/b,I11b with a≈ 6.023, b≈ 8.504, c≈ 6.062 A, α ≈ β ≈γ ≈ 90.0◦ , and do not agree with the space group Pnma(a≈ 6.023, b≈ 8.504, c≈ 6.062 A) and I2/m (a≈ 6.023,

Fig. 3 The Rietveld plot ofX-ray diffraction data ofBBP-10 with two phases

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Fig. 4 SAED patterns along different direction indexes in orthorhombic (a1, a2, a3, a4, and a5) and triclinic (b1, b2, b3, b4, and b5) lattice, andthe Rietveld plot of X-ray diffraction data (c) for BBP9

b≈ 8.504, c≈ 6.062 A, β ≈ 90.0◦). Therefore, our dataconfirm that the space group Imma can be used to describethe structure of BaPbO3 at room temperature (usually, welike to use the highest possible space group to describethe structure of a compound). The powder X-ray diffrac-tion data obtained by us can be fitted well with this spacegroup as shown in Fig. 2f. The refinement details arelisted in Table 1.

As reported, BBP10 with the nominal formulaBaPb0.90Bi0.10O3−δ may be tetragonal [10] (I4/mcm,a= b ≈ √

2ap, c≈ 2ap; ap, the lattice parameter a ofthe simple cubic perovskite), orthorhombic [11] (Imma,a≈ √

2 ap, b≈ 2ap, c≈ √2 ap), or biphasic (tetragonal

plus orthorhombic) [25]. Our results show that BBP10 isbiphasic, orthorhombic plus triclinic. The powder X-raydiffraction patterns of BBP10 can be fitted well with thetwo phases as shown in Fig. 3. The details of the refinementare listed in Table 1.

Similarly, BBP9 may also be tetragonal [10] (I4/mcm,a=b≈ √

2ap, c≈ 2ap), orthorhombic [11] (Imma, a≈ √2p,

b≈ 2ap, c≈ √2ap), or biphasic (tetragonal plus orthorhom-

Fig. 5 The volume of unit cell of the phases in the samples

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bic)[25]. The diffraction conditions for I4/mcm and Immaare hkl: h+k+l= 2n; 0kl: k, l= 2n and hkl: h+k+l= 2n;and hk0: h, k= 2n, respectively. The SAED patterns ofBBP9 are shown in Fig. 4a. It is found that if the patternsare indexed with a≈ 6.05, b ≈ 8.61, c ≈ 6.05 A, α ≈90◦, β ≈90◦ , γ ≈90◦ , the diffraction conditions hkl:h+k+l= 2n can be agreed, but the conditions 0kl: k, l= 2nand hk0: h, k= 2n are not agreed. Therefore, the spacegroups I4/mcm and Imma should not be used to describethe structure of BBP9. As the X-ray diffraction patterns ofBBP9 is very similar to that for BBP1(that is BaBiO3), thestructure model of BaBiO3 was used to describe BBP9. Itis found that the SAED patterns of BBP9 can be indexedwell with the space group P1 with a≈ 6.06 A, b≈ 6.04,c≈ 6.06 A, α ≈ 60.19◦, β ≈59.83◦, γ ≈ 60.09◦ asshown in Fig. 4b. The powder X-ray diffraction patterns forBBP9 can be fitted well with the space group P1 as shownin Fig. 4c.

As for BBP8 to BBP2, similar cases are found as thatfor BBP9. The powder X-ray diffraction patterns for BBP8to BBP2 can be fitted well with the structural model for

BaBiO3. The volumes of the unit cell for BBP1 to BBP11are shown in Fig. 5. It is found that the volume of the unitcell decreases linearly with the increase of the amount of Pbin the samples.

The magnetic susceptibilities of the samples BBP1 toBBP11 were measured. Only the samples BBP8, BBP9, andBBP10 show superconductivity with Tc around 11 K. Theirtemperature-dependent magnetic susceptibilities are shownin Fig. 6. In addition, the resistance of BBP9 was measuredfrom 2 to 20 K, which confirms that the BBP9 is a super-conductor with Tc around 11 K. This agrees well with theprevious reports by other researchers. The shielding volumefractions of the three samples are also shown in Fig. 6. Thesuperconductive volume fraction (shielding volume frac-tion) measured from the present samples is very small eventhe X-ray diffraction data show that BBP8 and BBP9 aresingle phase without observable impurities. Of course, thesuperconductive volume fraction for the two-phase sampleBBP10 is less than BBP8 and BBP9. The reason for thisphenomenon is complex and not clear. One may argue thatduring the measurement, only the surface of a supercon-

Fig. 6 The temperature-dependent magnetic susceptibilities and shielding volume fraction of BBP8 (a), BBP9 (b), BBP10 (c), and the temperaturedependent resistance of BBP9 (d)

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Fig. 7 The Rietveld plot of X-ray diffraction data (a), the temperature-dependent magnetic susceptibilities (b), the EDS of two kinds of particles(c, d) of BBP1K

ductor has a contribution, the core can be omitted. Then theshielding volume fraction should be less than 1. One mayalso argue that the superconductive phase is beyond the nor-mal phase (maybe we can call them as the diffraction phase,which means that these phases can be distinguished by X-ray, neutron, and electron diffraction patterns), the presentdiffraction method could not distinguish the superconduc-tive phase from the nonsuperconductive phases. Then, it iseasy to understand that the shielding volume fraction for thesingle phase BBP8 and BBP9 is far less than 1, and is dif-ferent from each other. At this case, the shielding volumefractions for other samples are not shown.

3.2 Crystal Structure and Superconductivityof Ba1−xKzBi1−yPbyO3(0.0 ≤ y ≤ 1.0)

It is found that there are four kinds of case for the sam-ples BBP1K to BBP11K: (1) three phases appear in BBP1K,(2) two phases appear in BBP2K to BBP6K, (3) onephase appears in BBP7K to BBP9K, and (4) BBP10K andBBP11K do not show superconductivity. Then, no detailson BBP10K and BBP11K are mentioned below. Supercon-ductivity is found for the samples BBP1K to BBP9K, thedetails for these samples are shown below.

3.2.1 BBP1K

The Rietveld refinement of the X-ray diffraction data ofBBP1K indicates that there are three phases in BBP1Kas shown in Fig. 7a. They all crystallize in space groupP1 with pseudo-cubic lattice parameter a about 4.348 A(noted as phase A), 4.341 A (phase B), and 4.289 A (phaseC), respectively. The ratio of phase A:phase B:phase Cis 3.9(3):7.4(3):1.0 suggested by the Rietveld refinement.BBP1K shows superconductivity with Tc around 30 K asshown in Fig. 7b. According to the work published by Petet al. [26], the superconductivity shown by BBP1K may beinduced by phase C, whose pseudo-cubic lattice parame-ter a is among the range showing 30 K superconductivityfor Ba1−xKxBiO3. The amount of K in the sample BBP1Khas been carefully analyzed by EDS method performed onhigh-resolution electron microscropy JEM2100F after con-sidering that BBP1K has at least three phases. Most of theparticles analyzed show no the signal for K as shown inFig. 7c, only about 10 % of the particles analyzed showthe signal for K as shown in Fig. 7d (Cu and C are dueto micro grid to containing the sample, Fe and Cr, aredue to sample holder). According to this, it may be sug-geted that there are no K in phase A and phase B, and

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the K mainly apprears in phase C. The lattice shrinkage ofthe phases A and B from the precursor BaBiO3 is there-fore attibuted to the deficiency of Ba in the A site ofABO3 perovskite.

3.2.2 BBP2K to BBP6K

It is found that there are two phases in BBP2K to BBP6Kas indicated by the Rietveld refinement as shown in Fig. 8a.The two phases all crystallize in space group P1. The cor-responding lattice parameters decrease comparing to theirprecursor. No K is found by checking about twenty parti-cles of each BBP2K to BBP6K by EDS method as shown inFig. 8b for BBP3K. Magnetic measurements show that all of

these samples exhibiting superconductivity with Tc decreas-ing from 25 K for BBP2k to 15 K for BBP6K, which isshown in Fig. 8.

3.2.3 BBP7K to BBP9K

The Rietveld refinement of the X-ray diffraction for BBP7Kto BBP9K shows that there is one phase in them as shownin Fig. 9. It is found also by EDS that there is no K

in these samples. Magnetic measurements show that theyshow superconductivity with Tc about 11 K. In order tomeasure the resistance of BBP7K between 2 and 20 K,the sample BBP7K was pressed into pellet and heating at500◦ C for 4 h, and noted as BBP7K-500, which was also

Fig. 8 The Rietveld plot of X-ray diffraction data (a) of BBP3K, the EDS of BBP3K (b), the temperature dependent magnetic susceptibilities ofBBP2K (c), BBP3K (d), BBP4k with zero-field cooling and 100 Oe field cooling (e), BBP5K (f), BBP6k (g)

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Fig. 9 The Rietveld plot of X-ray diffraction data (a) of BBP7K, the EDS of BBP7K (b), the temperature-dependent magnetic susceptibilities ofBBP7K (c), BBP7K-500 (treated again at 500◦ C for 4 h) (d), BBP8k (f), BBP9K (g), and the temperature dependent resistance of BBP7k-500 (e)

Fig. 10 The volume of unit cell (a) of the phases in the samples and transition temperature Tc (b) found in the samples

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confirmed by magnetic measurement to show superconduc-tivity as shown in Fig. 9d. The temperature-dependenceresistant of BBP7K-500 confirmed that BBP7K-500 wassuperconductor with Tc at 11 K.

4 Summary

The series of BaBi1−yPbyO3 (0 .≤ y .≤ 1) hasbeen synthesized by solid-state reaction. X-ray andselected area electron diffraction data confirm thatBaBi1−yPbyO3(0 .≤ y . ≤ 0.88) crystallizes in spacegroup P1 and BaBi1−yPbyO3 (0.93 .≤ y .≤ 1) crystal-lizes in space group Imma. The samples with the nomi-nal formula BaBi1−yPbyO3(y = 0.70, 0.80, 0.90) showssuperconductivity with transition temperature (Tc) around11 K. When BaBi1−yPbyO3 (0 .≤ y .≤ 0.80) was treatedwith KOH and KF at 450◦C, the corresponding sam-ples with the nominal formula Ba1−xKzBi1−yPbyO3 wereobtained. The corresponding reaction is found to be topotac-tic because the topological structure of BaBi1−yPbyO3 andBa1−xKzBi1−yPbyO3 is the same.

The sample Ba1−xKzBiO3 (BBP1K) consists of threephases, which may all crystallize in space group P1. Twoof them do not contain K , and the third phase con-tains K which may be contributor of the superconductivitywith Tc around 30 K found in this sample. The sam-ples Ba1−xKzBi1−yPbyO3 (y = 0.1, 0.2, 0.3, 0.4, and 0.5,noted as BBP2K, BBP3k, BBP4K, BBP5K, and BBP6K,respectively) consist of two-phase crystallizing in spacegroup P1. The EDS data show that there is no K in thesamples, which mean that the samples can be noted asBa1−xBi1−yPbyO3.The decrease of the volume of unit cellshown in Fig. 10 agrees well with this suggestion. Super-conductivity with Tc around 20 K is found for these sam-ples, which means that new superconductors may appear,because as we know, there is no report on such materi-als. More work is needed to confirm this observation. Thesamples Ba1−xKzBi1−yPbyO3 (y = 0.6, 0.7, and 0.8, notedas BBP7K, BBP8k, and BBP9K, respectively) consist ofone-phase crystallizing in space group P1. No K is foundin these samples by EDS data. Superconductivity with Tc

about 11 K was confirmed for BBP7K.

Acknowledgments This work is supported by the National KeyBasic Research Project of China (2010 CB833103) and the NationalNatural Science Foundation of China (Grant 21271014).

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