Enhanced superconducting properties of double-chain based superconductor Pr_{2}Ba_{4}Cu_{7}O_{15-δ} synthesized by citrate pyrolysis technique
Kazuma Honnami, Michiaki Matsukawa, Tatsuya Senzaki, Tomoki Toyama, Haruka Taniguchi, Koichi Ui, Takahiko Sasaki, Kohki Takahashi, Makoto Hagiwara, Fumihiko Ishikawa
EEnhanced superconducting properties of double-chain based superconductorPr Ba Cu O − δ synthesized by citrate pyrolysis technique Kazuma Honnami, Michiaki Matsukawa, ∗ Tatsuya Senzaki, Tomoki Toyama, Haruka Taniguchi, Koichi Ui, Takahiko Sasaki, and Kohki Takahashi Faculty of Science and Engineering, Iwate University, Morioka 020-8551, Japan Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Dated: February 9, 2021)We report the enhanced superconducting properties of double-chain based superconductorPr Ba Cu O − δ synthesized by the citrate pyrolysis technique. The reduction heat treatmentin vacuum results in the appearance of superconducting state with T c =22-24 K, accompanied bythe higher residual resistivity ratios. The superconducting volume fractions are estimated from theZFC data to be 50 ∼ R H of the 48-h-reduced superconducting sample is determined to be -0.5 × − cm /C at 30 K, sug-gesting higher electron concentration. These findings have a close relationship with the enhancedsuperconducting properties, leading to the phase diagram of the present samples. PACS numbers: 74.25.Ha,74.25.F-,74.90.+n
I. INTRODUCTION
Since the discovery of high- T c copper-oxide supercon-ductors, researches have focused on the unconventionalsuperconductivity on the two-dimensional CuO planesin some cuprates. In quasi one-dimensional (1D) lad-der system without CuO planes, it is well known thatthe superconductivity at T c = 12 K appears only underthe application of high pressure. In a previous study ofPr-based cuprates with metallic CuO double chains andinsulating CuO planes , Pr Ba Cu O − δ is found tobe a new superconductor with a higher T c (15 K) af-ter a reduction treatment. A nuclear quadrupole reso-nance (NQR) study has revealed that the newly discov-ered superconductivity is realized at the CuO double-chain block. Structurally, the Pr-based cuprates, PrBa Cu O − δ (Pr123) and PrBa Cu O (Pr124), are identical totheir corresponding Y-based high- T c superconductors,YBa Cu O − δ (Y123) and YBa Cu O (Y124). Pr123and Pr124 compounds have insulating CuO planes andare non-superconductive. The suppression of supercon-ductivity in the Pr substitutes has been explained by thehybridization of Pr-4 f and O-2 p orbitals. The crystalstructure of Pr124 with CuO double chains differs fromthat of Pr123 with CuO single chains. It is well knownthat CuO single chains in Pr123 and CuO double chainsin Pr124 show semiconducting and metallic behaviors,respectively. The carrier concentration of doped doublechains of Pr124 is difficult to vary, because it is thermallystable up to high temperatures.The compound Pr Ba Cu O − δ (Pr247) is an inter-mediate between Pr123 and Pr124. In this compound,CuO single-chain and double-chain blocks are alternatelystacked along the c -axis such as { -D-S-D-S- } sequence (see Fig.1). Here, S and D denote CuO single-chain anddouble-chain blocks along the b -axis, respectively. Thephysical properties of the metallic CuO double chains canbe examined by controlling the oxygen content along thesemiconducting CuO single chains. Anisotropic resistiv-ity measurements of single-crystal Pr124 have revealedthat metallic transport arises by the conduction alongthe CuO double chains. In oxygen removed polycrys-talline Pr Ba Cu O − δ , the superconductivity appearsat an onset temperature T c , on of ∼
15 K. Hall coefficientmeasurements of superconducting Pr247 with T c , on = 15K have revealed that at intermediate temperatures be-low 120 K, the main carriers change from holes to elec-trons, as the temperature decreases. Accordingly, thiscompound is an electron-doped superconductor. In ourprevious study, we examined the effect of magnetic fieldson the superconducting phase of Pr247. Despite of theresistive drop associated with the superconducting tran-sition, we found that the diamagnetic signal was stronglysuppressed as expected in the 1D superconductivity ofCuO double chains. We also reported the effect of pres-sure on magneto-transport properties in the supercon-ducting and normal phases of the metallic double chaincompound Pr Ba Cu O − δ . .In this paper, we demonstrate the magneto-transportproperties of Pr Ba Cu O − δ with T c , on (22-24 K) ac-companied by the strongly metallic conduction, for ourunderstanding of the effect of magnetic field on the super-conducting properties of electron-doped metallic double-chain compound. II. EXPERIMENT
Polycrystalline samples of Pr Ba Cu O − δ were syn-thesized by using the citrate pyrolysis technique. a r X i v : . [ c ond - m a t . s up r- c on ] F e b
10 20 30 40 50 602 (deg.) I n t e n s it y ( a r b . un it ) ( ) ( ) As-sintered ( a )
10 20 30 40 50 602 (deg.)film in 10T ( ) ( )( ) ( )( ) ( ) I n t e n s it y ( a r b . un it ) ( b ) Fig. 1: (color online)(a) X-ray diffraction patterns of as-sintered polycrystalline Pr Ba Cu O − δ . The (004) peakcorresponds to one of typical Miller indexes of Pr247. Thecalculated curve is obtained using the lattice parameters inthe text. Inset shows the crystal structure of Pr247 withCuO single-chain and double-chain blocks along the b -axis.(b)X-ray diffraction pattern for polycrystalline film preparedby an electrophoretic deposition technique under 10 T. Themagnetic field was applied parallel to the direction of appliedelectric field between anode and cathode electrodes. In the first step, stoichiometric mixtures of high purityPr O , Ba(NO ) , and CuO were dissolved in a nitricacid solution at50-60 ◦ C. After adding citric acid andneutralizing it by aqueous ammonia, we then obtainedthe porous products through the self-ignition process us-ing halogen lamp stirrer. In the next step, the precursorswere ground and resultant fine powders were annealedunder ambient oxygen pressure at 890-891 ◦ C for an ex-tended period over 110-120h. In particular, we used threezone controlled electric furnace, in order to attain a ho-mogeneous temperature distribution.For scanning electron microscope measurements, thePr Ba Cu O polycrystalline film on Ag substrate was Fig. 2: (color online) SEM image for polycrystalline film pre-pared by an electrophoretic deposition technique under 10 T. fabricated from the single-phase as-sintered powdersby an electrophoretic deposition technique. The elec-trophoretic deposition was conducted in the acetone andiodine bath under the application of electric voltage upto 300 V for 120 s. We set Pt and Ag plates as an-ode and cathode electrodes, respectively. Furthermore,we performed the magnetic field assisted electrophoreticdeposition process for the fabrication of c -axis alignedPr Ba Cu O polycrystalline film. Here, the magneticanisotropy of rare earth ion Pr including Pr Ba Cu O shows that the magnetic susceptibility of χ H (cid:107) c is largerthan that of χ H ⊥ c . A magnetic field up to 10 T was ap-plied to the colloid bath including the suspended Pr247powders using a superconducting magnet with a 100 mmdiameter bore at room temperature at the High FieldLaboratory for Superconducting Materials, Institute forMaterials Research (IMR), Tohoku University. The mag-netic field was applied parallel to the direction of appliedelectric field for the electrophoretic deposition.We performed X-ray diffraction measurements on theproduced samples at room temperature with an UltimaIV diffractometer (Rigaku) using Cu-K α radiation. Thelattice parameters were estimated from the x-ray diffrac-tion data using the RIETAN-FP program.The dc magnetization was measured at a magnetic fieldof 50 mT under the field cooling process using a super-conducting quantum interference device magnetometer(MPMS,Quantum Design).The oxygen in the as-sintered sample was removed byreduction treatment in a vacuum at 500 ◦ C, yielding asuperconducting material. Typical dimensions of the pel-letized rectangular sample were 4 . × . × . . X-ray diffraction data revealed that the as-sintered poly-crystalline samples are an almost single phase with anorthorhombic structure ( Ammm ), as shown in Fig.2( a ).The lattice parameters of the as-sintered sample are a = 3 . b = 3 . c = 50 . . The oxygen deficiencies in the 48 hand 72 h reduced samples in a vacuum were estimatedfrom gravimetric analysis to be δ = 0 .
43 and 0.54, re-spectively. As a function of the oxygen deficiency, the T c , on rises rapidly at δ ≥∼ .
2, then monotonically in-creases with increasing δ , and finally saturates around26-27 K at δ ≥∼ . Accordingly, we expect that thecarriers in the present sample are concentrated aroundthe optimally doped region.The electric resistivity in zero magnetic field was mea-sured by the dc four-terminal method. The magneto-transport up to 9 T was measured by the ac four-probe method using a physical property measuring sys-tem (PPMS, Quantum Design), increasing the zero-field-cooling (ZFC) temperatures from 4 K to 40 K. The highfield resistivity (up to 14 T) was measured in a supercon-ducting magnet at IMR, Tohoku University. The electriccurrent I was applied longitudinally to the sample ; con-sequently, the applied magnetic field H was transverse tothe sample (because H ⊥ I ). We performed Hall coeffi-cient measurements on the as-sintered and 48 h reducedsamples with the five-probe technique using PPMS andthe 15T-superconducting magnet. The dc magnetiza-tion was performed under ZFC in a commercial super-conducting quantum interference device magnetometer(Quantum Design, MPMS). III. RESULTS AND DISCUSSION
Figure2( a ) shows X-ray diffraction (XRD) patternsof as-sintered polycrystalline Pr Ba Cu O − δ (Pr247).The (004) peak corresponds to one of typical Miller in-dexes of Pr247. The calculated curve is obtained usingthe lattice parameters. The inset of Fig. 1( a ) displaysthe crystal structure of Pr247 with CuO single-chain anddouble-chain blocks along the b -axis.For comparison, X-ray diffraction pattern of polycrys-talline film prepared by an electrophoretic depositiontechnique under 10 T is shown in in Fig. 1( b ). We notethat the XRD pattern of the Pr247 film fabricated bythe electrophoretic deposition process without the ap-plied magnetic field (not shown here) was the same asthat of the Pr247 powders. (00 l ) peaks did not appearexcept for the (004) and (0026) peaks. When the mag-netic field was applied parallel to the direction of appliedelectric field, the peak intensities of (00 l ) were stronglyenhanced as shown in Fig. 1( b ), indicating the c-axisalignment of polycrystalline grains. The SEM image ofthe Pr247 film in Fig. 2 reveals that plate-like grainswith sub micron size are homogeneously dispersed.Now, the temperature dependences of electric resistiv-ities of the as-sintered, 48-h-reduced and 72-h-reducedPr Ba Cu O − δ compounds are shown in Fig. 3( a ).The reduction heat treatment on the as-sintered samplein vacuum results in the appearance of superconduct-ing state with T c =22-24 K, accompanied by the stronglymetallic properties over a wide range of temperature. ( m c m ) T (K) ( a ) -0.008-0.006-0.004-0.0020 0 5 10 15 20 25 3048h72h ( e m u / g O e ) T (K)ZFC 5mT -5 -5 -5 -5 -5
18 20 22 24 2648h72h ( e m u / g O e ) T (K) T c,on =22.5 KT c,on =24 K ( b ) Fig. 3: (color online)(a) Temperature dependences of electricresistivities of the as-sintered, 48-h-reduced and 72-h-reducedPr Ba Cu O − δ compounds. (b) low-temperature depen-dences of magnetic susceptibilities χ of the 48-h-reduced and72-h-reduced superconducting samples measured at 5 mT un-der ZFC scan. In the inset, the magnified data are plotted toclarify the definition of T c,on . Here, we define the residual resistivity ratio (RRR) as ρ (300K)/ ρ (30K), For the present samples reduced in vac-uum, we obtained the higher RRR values (10 ∼ . Furthermore, to check the bulk superconductivity, weperformed to measure low-temperature dependences ofmagnetic susceptibilities χ of the 48-h and 72-h-reducedsuperconducting samples measured at 5 mT under ZFCscan. Figure 3( b ) exhibits diamagnetic signals below T c , on =22.5 K and 24.0 K for the 48-h-reduced and 72-h-reduced samples, respectively. In addition, the supercon-ducting volume fractions due to the shielding effect areestimated to be 50 ∼
55% from the ZFC values at 5 K,which are much higher than the previous data ( ∼ In the inset of Fig. 3( b ) , the magnified data are plot- TABLE I: Physical and superconducting properties for Pr Ba Cu O − δ . In details, see the corresponding text and references. δ and RRR denote oxygen deficiency and residual resistivity ratio ρ (300K)/ ρ (30K), respectively. H ∗ c is defined from the fieldsweep data at fixed temperatures as the critical field where the zero-resistance state is violated with increasing the field.Synthesis Reduced time δ RRR f SC T c , on T c , zero H ∗ c R H (30K)(%) (K) (K) (T) (10 − cm /C)citrate pyrolysis 48h 0.43 10 55 22 18 10.6(4.2K) -0.5citrate pyrolysis 72h 0.54 12 50 24.3 18 - -citrate pyrolysis 48h 0.52 a a a a a ∼ b high pressure
48h 0.5 - 30 16 ∼
10 - -1.5 a see ref. , b ref. ted to clarify the definition of T c , on . The characteristicvalues for the present and previous samples are listed inTable I.Next, we try to measure the magneto-transport prop-erties of the reduced samples, to examine the magneticeffect on the superconducting phase of the Pr247 com-pound. Figure 4( a ) shows the low-temperature depen-dences of electric resistivities of the 48-h-reduced super-conducting Pr Ba Cu O − δ compound measured underzero field and applied fields of 10 and 14T.In zero field, the resistivity starts to decrease around T c , on = 22 K, then follows a rapid drop, and finallyachieves a zero-resistance state at T c , zero = ∼
18 K. Theobserved transition width T c , on = 22 K is relatively sharpin comparison with the published data. Inset plots themagneto-resistance data of the 48-h-reduced sample at4.2 and 30 K. At the high field of 10 T, we observed T c , on = 18 K and T c , zero = ∼ ρ are negligibly small with those of the normal state at 30K. These findings strongly suggest that for the presentsample the superconducting properties under relativelyhigh fields are considerably improved. For the previousPr247 samples, it has been reported that the critical fieldis as low as a few tesla at low temperatures.In Fig. 4( b ) , we show the low-temperature depen-dences of electric resistivities of the 72-h-reduced super-conducting Pr Ba Cu O − δ compound measured at theseveral applied fields ( H = 0, 1, 3, 6 and 9 T). The insetdisplays the enlarged data of the 72-h-reduced samplearound T c , on = 24 . T c , zero = ∼
18 K and 5 K, at 0 T and at 9 T, respec-tively. Here, we evaluate from the magneto-transportdata the temperature dependence of the superconduc-tive critical field, to establish the superconducting phasediagram. The onset T c ( T c , on ) is determined from theintersection between the two lines extrapolated from thenormal and superconducting transition resistivity data,just above and bellow T c , respectively. (see Fig.4). Thezero-point T c ( T c , zero ) denotes the value of the criticaltemperature reaching the zero-resistance state. The crit- ical field at 0 K is estimated to be 25 T from fitting thedata of the onset T c using the parabolic function formulaof the critical field. There are quite differences in thecritical fields determined from T c , zero between the presentand previous samples, strongly suggesting the enhancedsuperconducting properties in the presence of magneticfield as represented by a right arrow in Fig. 5.Finally, in Fig.6, we show the temperature depen-dences of the Hall coefficients R H for the as-sintered non-superconducting and 48-h-reduced superconducting sam-ples of Pr Ba Cu O − δ . The R H data of the as-sinteredsample are very similar, in the both magnitude and tem-perature dependence, to those of the previous sample.For the 48-h-reduced sample, the R H data exhibit nega-tive values in the limited temperature range between 30and 80 K, accompanied by electron doping due to the re-duced heat treatment in vacuum. Moreover, we estimate R H = − . × − cm /C at 30 K, which is as about halfas the published data. , indicating higher carrier con-centration. These results have a close relationship withthe enhanced superconducting properties, leading to thesuperconducting phase diagram of the present samples.For comparison, the physical and superconducting prop-erties for Pr Ba Cu O − δ compounds are summarizedin Table I. IV. SUMMARY
We have demonstrated the enhanced superconduct-ing properties of double-chain based superconductorPr Ba Cu O − δ synthesized by the citrate pyrolysistechnique using the 3-zone controlled electric furnace.When the magnetic field is applied parallel to the direc-tion of applied electric field, the peak intensities of (00 l )are strongly enhanced, indicating the c-axis alignment ofpolycrystalline grains. The SEM image of the Pr247 filmreveals that plate-like grains with sub micron size arehomogeneously dispersed. In spite of the polycrystallinebulk samples, we obtained the higher residual resistivityratio ranging from 10 to 12 for the 48-72 h reduction.The reduction heat treatment on the as-sintered samplein vacuum results in the appearance of superconduct-ing state with T c =22-24 K, accompanied by the metallicproperties over a wide range of temperature. The super- ( m c m ) T c,on =22 K
48h reduced H c =10.6 T ( m c m ) ( a ) ( m c m )
72h reduced ( m c m ) T c,on =24.3 K ( b ) Fig. 4: (color online) (a) Low-temperature dependencesof electric resistivities of the 48-h-reduced superconductingPr Ba Cu O − δ compound measured under 0T, 10T, and14T. Inset plots the magneto-resistance data of the 48-h-reduced sample at 4.2 K and 30 K. (b) Low-temperaturedependences of electric resistivities of the 72-h-reduced su-perconducting Pr Ba Cu O − δ compound measured at theseveral applied fields ( H = 0, 1, 3, 6 and 9 T). The insetdisplays the enlarged data of the 72-h-reduced sample around T c . conducting volume fractions are estimated from the ZFCdata to be 50 ∼ R H data exhibit negative values in the limitedtemperature range between 30 and 80 K, accompanied byelectron doping due to the reduced heat treatment in vac-uum. Moreover, we estimate R H = − . × − cm /Cat 30 K, which is as about half as the published data, H ( T ) T(K)
SC phase Normalphase
Fig. 5: (color online) Temperature dependence of the su-perconducting (SC) critical field of the reduced samples ofPr Ba Cu O − δ . The onset T c ( T c , on ) is determined fromthe resistivity data as described in the text. For comparison,the previous data of the reduced Pr247 are referred (opensymbol). The solid curve separating the superconducting andnormal phases was plotted using the parabolic function for-mula of the critical field with H c2 (0)=25 T. -1-0.500.511.5 0 20 40 60 80 100As-sintered48h reduced R H ( - c m / C ) T(K)
Fig. 6: (color online) Temperature dependences of the Hallcoefficients R H for the as-sintered non-superconducting and48-h-reduced superconducting samples of Pr Ba Cu O − δ . indicative of higher carrier concentration. These resultshave a close relationship with the enhanced supercon-ducting properties, leading to the superconducting phasediagram of the present samples. V. ACKNOWLEDGE
This work was supported in part by MEXT Grands-in-Aid for Scientific Research (JPSJ KAKENHI Grants No. JP19K04995). We thank Mr. K. Sasaki for the SEMmeasurement and M. Nakamura for his assistance in thePPMS experiments. ∗ Electronic address: [email protected] M. Uehara, T. Nagata, J. Akimitsu, H. Takahashi, N. Mori,and K. Kinoshita, J. Phys. Soc. Jpn., 65 (1996) 2764. M. Matsukawa, Y. Yamada, M. Chiba, H. Ogasawara, T.Shibata, A. Matsushita, and Y. Takano, Physica C 411(2004) 101. S. Watanabe, Y. Yamada and S. Sasaki, Physica C 426-431(2005) 473. L. Soderholm, K. Zhang, D. G. Hinks, M. A. Beno, J. D.Jorgensen,C. U. Segre, I. K. Schuller, Nature 328 (1987)604. S. Horii, Y. Yamada, H. Ikuta, N. Yamada, Y. Kodama,S. Katano,Y. Funahashi, S. Morii, A. Matsushita, T. Mat-sumoto, I. Hirabayashi, and U. Mizutani,Physica C 302(1998) 10. R. Fehrenbacher and T. M. Rice, Phys. Rev. Lett. 70(1993) 3471. T. Mizokawa, C. Kim, Z. -X. Shen, A. Ino, T. Yoshida, A.Fujimori, M. Goto, H. Eisaki, S. Uchida, M. Tagami, K.Yoshida, A. I. Rykov, Y. Siohara, K. Tomimoto, S. Tajima,Yuh Yamada, S. Horii, N. Yamada, Yasuji Yamada, and I.Hirabayashi, Phys. Rev. Lett. 85 (2000) 4779. P. Bordet, C. Chaillout, J. Chenavas, J. L. Hodeau, M.Marezio,J. Karpinski, and E. Kaldis, Nature 334 (1988)596. Y. Yamada, S. Horii, N. Yamada, Z. Guo, Y. Kodama,K. Kawamoto,U. Mizutani, and I. Hirabayashi, Physica C231(1994)131. S. Horii, U. Mizutani, H. Ikuta, Y. Yamada, J. H. Ye, A.Matsushita, N. E. Hussey, H. Takagi, and I. Hirabayashi, Phys. Rev. B61 (2000) 6327. A. Matsushita, K. Fukuda, Y. Yamada, F. Ishikawa, S.Sekiya,M. Hedo, and T. Naka, Science and Technology ofAdvanced Materials 8 (2007) 477. T. Chiba, M. Matsukawa, J. Tada, S. Kobayashi, M. Hagi-wara, T. Miyazaki, K. Sano, Y. Ono, T. Sasaki, andJ.Echigoya, J. Phys. Soc. Jpn., 82 (2013) 074706. M. Kuwabara, M. Matsukawa, K. Sugawara,H. Taniguchi,A. Matsushita, M. Hagiwara, K. Sano, Y. Ono, and T.Sasaki, J. Phys. Soc. Jpn., 82 (2013) 105003. K. Koyama, A. Junod, T. Graf, G. Triscone, and J. Muller,
Physica C , vol.185-189, 66-70, 1991. M. Hagiwara, T. Shima, T. Sugano, K. Koyama, and M.Matsuura,
Physica C , vol. 445-448, 111-114, 2006. M. Kawachi, N. Sato, E. Suzuki, S. Ogawa, K. Noto, andM. Yoshizawa,
Physica C , vol. 357-360, 1023-1026. M. Kawachi, N. Sato, K. Noto and M. Yoshizawa,
PhysicaC , vol. 802-805, 802-805, 2002. X. Xu, A. Carrington, A. I. Coldea, A. Enayati-Rad, A.Narduzzo, S. Horii, and N. E. Hussey,
Phys. Rev. B , vol.81, 224435, 2010. Y. Yamada and A. Matsushita, Physica C 426-431 (2005)213. M. Hagiwara, S. Tanaka, T. Shima, K. Gotoh, S. Kanda,T. Saito, and K. Koyama, Physica C 468 (2008) 1217.21