Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a

Subscriber access provided by LAURENTIAN UNIV

Article

Hydrothermal synthesis, crystal structure, and superconductivity of a double perovskite Bi-oxide Mirza H. K. Rubel, Takahiro Takei, Nobuhiro Kumada, M. Mozahar Ali, Akira Miura, Kiyoharu Tadanaga, Kengo Oka, Masaki Azuma, Masatomo Yashima, Kotaro Fujii, Eisuke Magome, Chikako Moriyoshi, Yoshihiro Kuroiwa, James R. Hester, and Maxim Avdeev Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.5b02386 • Publication Date (Web): 23 Dec 2015 Downloaded from http://pubs.acs.org on January 8, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Chemistry of Materials is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials

Hydrothermal synthesis, crystal structure, superconductivity of a double-perovskite Bi oxide 1

1

1

1

2

and 2

Mirza H. K. Rubel , Takahiro Takei , Nobuhiro Kumada *, M. Mozahar Ali , Akira Miura , Kiyoharu Tadanaga , 3 4 5 5 6 6 Kengo Oka , Masaki Azuma , Masatomo Yashima , Kotaro Fujii , Eisuke Magome , Chikako Moriyoshi , Yoshihiro 6 7 7 Kuroiwa , James R. Hester , and Maxim Avdeev 1

Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae-cho, Kofu 400-8511, Japan Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan 3 Faculty of Science and Engineering, Chuo University, 112-8551, 1-13-27, Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan 4 Materials and Structural laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Kanagawa 226-8503, Japan 5 Department of Materials Science and Engineering, Tokyo Institute of Technology, 2-12-1-W4-17, Ookayama, Meguro-ku, Tokyo 152-8551, Japan 6 Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 7398526, Japan 7 Bragg Institute, Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia 2

ABSTRACT: Double-perovskite Bi oxides are a new series of superconducting materials, and their crystal structure and superconducting properties are under investigation. In this paper, we describe the synthesis and characterization of a new double-perovskite material that has an increased superconductive transition temperature of 31.5 K. The structure of the material was examined using powder neutron diffraction (ND), synchrotron X-ray diffraction (SXRD), and transmission electron microscopy (TEM). Rietveld refinement of the sample based on ND and SXRD data confirmed an A-site-ordered (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double-perovskite-type structure with the space group Im-3m (No. 229). This structural analysis revealed the incorporation of Na with Bi in the structure and a bent bond between (Na, Bi)–O–(Na, Bi). TEM analyses also confirmed a cubic double-perovskite structure. This hydrothermally synthesized compound exhibited a large shielding volume fraction, exceeding 100%, with onset of superconductivity at ~31.5 K. Its electrical resistivity dropped near onset at ~28 K, and zero resistivity was confirmed below 13 K. The calculated band structure revealed that the metallicity of the compound and the flatness of the conduction bands near the Fermi level (EF) are important for the appearance of superconductivity.

1. Introduction Among mixed metal oxides, perovskite-type Bi oxides are the 1,2 most well-known, and many properties of these perovskites have been reported. This wide range of properties arises due to the partial substitution of cations at positions A and B in multi-component perovskites, giving rise to substituted compounds and forming both simple- and double3,4 perovskite-type structures. The incorporated elements, as well as their partial substitutions and/or impurities, significantly affect the superconducting properties of perovskites. Another important aspect of perovskites is related to the stability of mixed or unusual oxidation states in the crystal structures, which greatly favor the development 5 of high-temperature superconductivity. However, there is little evidence of superconductivity in double-perovskite compounds because either different elements occupy the A and B sites or both are occupied in an ordered way. Recently, a new A-site-ordered superconductive double-perovskite bismuth oxide, (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12, with a transition temperature (Tc) of approximately 27 K has been 6 reported. This is the first example of the 3:1 ordering of

Ba:(Na, K) cations in perovskite at A sites among superconductive double-perovskite structures (with a 30% fraction of vacancies on the Na/K sites). The compound was synthesized under hydrothermal conditions at a relatively low temperature, and this probably favored the formation of an ordered structure. However, the presence of impurity peaks, additional phases, and a smeared transition at Tc was 6 observed in the reported double perovskite. Moreover, the possibility of mixing A-site-ordered and disordered phases cannot be discounted in this perovskite structure. Therefore, the discovery of superconductivity in the double-perovskite structure has inspired a further search for highly crystalline and high-quality samples of double-perovskite materials with improved superconducting properties. There are two general formulas for double perovskites: AʹAʹʹBO6 or A2BBʹO6, where the symbols ′ and ″ indicate the possible occupancies of either the A or B sites by different cations. Among double perovskites, those having the formula A2BBʹO6 (A: alkaline/alkaline-earth/rare-earth cations; B: transition cations) have been investigated for their magnetic 7 and magnetoresistive properties . On the other hand, AʹAʹʹBO6-type double perovskites have been studied for their

ACS Paragon Plus Environment

Chemistry of Materials 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

superconducting, 12 properties.

8,9

catalytic,

10,11

magnetic,

and dielectric

Figure 1. Crystal structure of (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite. The atoms at the Aʹ site in the center and at the eight corners are all K atoms. Ba atoms are at the Aʹʹ site. The Bi/Na atoms form a network of corner-sharing tilted (Bi/Na)O6 octahedra.

The ideal structure of these double-perovskite compounds can be viewed as a regular arrangement of corner-sharing BO6 and BʹO6 octahedra alternating along the three crystal directions. The crystal structure and physical properties of double-perovskite Bi oxides depend considerably on the size, valences, vacancies, and occupation possibilities of the Aʹ, Aʹʹ, B, and Bʹ cations. For instance, superconductive (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12 double perovskite has a cubic structure (Im-3m) with lattice parameter a = 8.5493(5) Å; however, when heated to 600 °C, it undergoes a structural change to form a simple cubic perovskite-type structure with 6 a = 4.3561(9) Å. Importantly, this compound, which was synthesized via hydrothermal reaction at 220 °C, no longer exhibited superconductivity after this structural change. Additionally, both a (Ba0.75K0.14H0.11)BiO3·nH2O double4 perovskite superconductor with a Tc of 8 K and another 13 double-perovskite Ba1-xKxBi1-yNayO3 structure in a nonsuperconducting form were fabricated by the hydrothermal method at 180 °C. Recently, we reported a new 3 superconductive simple perovskite bismuth oxide, (Ba0.82K0.18)(Bi0.53Pb0.47)O3, with a Tc of approximately 22.8 K prepared hydrothermally at 240 °C. Thus, the hydrothermal reaction temperatures and choice of starting materials, especially their molar ratios, were crucial for the fabrication of these Bi-based perovskites with superconducting properties. Samples of the previously reported A-site-ordered double6 perovskite bismuthate, (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12, showed small diffraction peaks due to an unknown impurity; in addition, shoulders to peaks between the d-spacings of 3.4244(1) Å and 3.1841(1) Å (indicated by arrow, inset Figure S1) were observed. These peaks made the refinement difficult, but they were finally revealed to be due to a twophase structure. Hence, the absence of impurities and shoulders of peaks in the X-ray diffraction (XRD) pattern of the double-perovskite phase is one of the most important findings in this study. In this study, we produced a double-perovskite-type structure with improved superconducting properties by optimizing the hydrothermal reaction conditions. Among the synthesized samples, the precursor of a single-phase doubleperovskite structure with a minimum number of impurities was only found at 240 °C (reaction temperature), with a

Page 2 of 8

maximum Tc of approximately 31.5 K. The combined crystal structure refinement was performed based on both powder neutron diffraction (ND) and synchrotron X-ray diffraction (SXRD) data on a highly-crystallized sample, providing a complete structural model for the synthesized double perovskite, as shown in Figure 1. The refinement 6 demonstrated that the reported double perovskite was different from that of the previous study. Notably, this double perovskite structure showed the incorporation of Na into Bi sites and a zigzag Bi–O–Bi bond, in contrast to the structures of the reported Ba1-xKxBiO3 and Sr1-xKxBiO3 14-16 superconducting systems. 2. Experimental and computational details Crystalline powder samples were synthesized under hydrothermal conditions in aqueous solutions with a Teflonlined autoclave (70 mL) using the starting materials, NaBiO3·nH2O, Ba(OH)2·8H2O, and KOH, in a 1:1:120 molar ratio, respectively, and distilled water (7.5 ml). The autoclave was tightly closed and heated to 180, 200, 220, 230, 240, 250, and 260 °C for 2 days. After cooling and depressurizing the autoclave, the products were separated by filtration, repeatedly washed with distilled water, and dried in air at 60 °C for 6 h for further characterization. The initial phases of the products were examined by XRD on a Rigaku X-ray diffractometer (RINT 2000V, RIGAKU) with graphite monochromatized CuKα radiation (λ = 1.54056 Å). The microstructure, morphology, and elemental distributions were investigated by a scanning electron microscope (SEM, JEOL JEM-6500F). The compositional homogeneity, nanoscale structural analysis, and electron diffraction patterns were studied using both bright-field and dark-field conditions by TEM (Tecnai Osiris FEI). The SXRD data were collected using a Debye–Scherrer camera installed at the BL02B2 powder diffraction beamline at SPring-8, Hyogo, Japan. The powder samples were sealed in a quartz glass capillary with an inner radius of 0.2 mm to collect long and slow scan data. The wavelength was calibrated to 0.41365 Å using CeO2 as the standard. High-temperature SXRD analysis was also performed from room temperature to 800 °C. Powder neutron diffraction (ND) measurements were performed in air at 22.1 °C with a neutron beam of wavelength 1.62124(4) Å. The scan covered a 2θ range of 15.0–160.0° with a step size of 0.1°/2θ. The diffraction measurements were carried out on an angle-dispersive-type neutron 17 diffractometer, Echinda, at the Open Pool Australian Light water reactor (OPAL) at the Bragg Institute, Australian Nuclear Science and Technology Organization (ANSTO). The combined Rietveld refinements from ND and SXRD data were 18 performed using FULLPROF to achieve a consistent structural model. During the refinement, the peak shape was approximated by a split pseudo-Voigt function, and the background was approximated with a 12-parameter Legendre polynomial, and these were simultaneously refined. The 19 crystal structure was visualized using VESTA. Thermal stability was investigated by thermogravimetric analysis 1 (TGA) at a heating rate of 10 °C min− from room temperature to 800 °C under flow of He gas. Chemical composition analysis was carried out using inductively coupled plasma (ICP) (SPS 3500 DD, Hitachi) and iodometric titration using

2


Page 3 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


an automatic titrator (TOA DKK AUT-701). The temperature dependence of the DC magnetic susceptibility was measured in both zero-field cooling (ZFC) and field-cooling (FC) modes over the temperature range 3.0–40.0 K in an external field of 10 Oe using a vibrating sample magnetometer (PPMS, Quantum Design). The electrical resistivity of the pellet sample was measured between 3.0 and 300.0 K using a standard four-probe method (PPMS, Quantum Design). The band structure and the atom-projected densities of state (DOS) were calculated by density functional theory (DFT) 20 calculations using CASTEP. The generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof 21 (PBE) exchange correlation functional was implemented. The Broyden–Fletcher–Goldfarb–Shanno (BFGS) minimization technique was employed to minimize the structural parameters. Geometry optimization was achieved 5 using convergence thresholds of 1×10− eV/atom. A k-point mesh of 6 × 6 × 6 grids and a plane-wave-energy cutoff (Ecut) of 500 eV were used for the calculations. CASTEP code allowed mixing and partial occupation of atoms in one atomic site ranging from 0.0 to 1.0 atomic concentration. It yielded structure and partial DOS for specific atomic sites instead of individual contribution even though containing more than one element.

3. Results and discussion 3.1 Structural refinement of a new double-perovskite

The short verticals lines indicate the positions of allowed Bragg reflections. Residual errors are plotted at the bottom of the figure.

Elemental analysis (ICP) detected all the component elements: Bi, Ba, K, and Na. The concentration of each element for the sample prepared at 240 °C was converted to a molar ratio of Bi:Ba:K:Na = 1:0.95:0.22:0.17. On the other hand, the molar ratio of each element for the sample synthesized at 220 °C was as follows: Bi:Ba:K:Na = 1:0.87:0.15:0.08. The molar concentrations of the elements changed with reaction temperature, although the starting materials remained the same for each sample preparation. Therefore, there is the potential for partial and alternate occupation of Na and/or K at either the A site or the B site. Furthermore, iodometric titration results confirmed the 5+ 3+ existence of both Bi and Bi in the samples, and their average Bi valence decreased from 4.76 to 4.08 with increasing reaction temperature from 180 to 260 °C. This 5+ reduction would be due to the thermal reduction of Bi , 5+ 24 which has been reported in many oxides with Bi . The average Bi valence for the sample prepared at 240 °C was 4.41, a value that is very similar to those of previously reported double perovskites and some simple perovskite 6,25,26 compounds. The observed Bi valence of 4.41 at 240 °C is significant in terms of the appearance and control of superconductivity in the family of Bi-based doubleperovskite superconductors.

For the sample prepared at 240 °C, the diffraction peaks indicate a highly crystalline powder. The powder was indexed as having a perovskite-like phase with superstructure peaks corresponding to A-site ordering (Figure S1). The systematic absences in the XRD pattern suggest the space group is Im-3m (No. 229), a similar finding to our previous studies and those of some other 6,12,22,23 reports. Table 1. Refined structural parameters and crystal data based on combined Rietveld refinement of ND and SXRD data for (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 prepared by a hydrothermal reaction at 240 °C. Numbers in the parenthesis are assumed standard deviations of the last significant digit.

Figure 2. (a) SXRD and (b) ND patterns and Rietveld refinement profiles of (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 cubic (Im-3m) doubleperovskite structure at room temperature. The markers and solid lines indicate the experimental and calculated profiles, respectively.

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Atoms

Site

K Ba Bi Na

2a 6b 8c 8c

Occupancy factor (g) 1.0 1.0 0.866(6) 0.114(6)

O

24h

1.0

x

y

Z

Biso (Å2)

0 0 1/4 1/4

0 1/2 1/4 1/4 0.2439(6) (5)

0 1/2 1/4 1/4

3.4(6) 0.60(5) 0.21(2) =B(Bi)

=y(O)

1.84(4)

0

Space group: Cubic Im-3m (No. 229). Unit cell parameter: a = 8.52933(5) Å. Number of formula units in a unit cell: Z = 2. 2 Reliability factors (ND): Rwp = 6.93%, Rp = 5.32% χ = 21.4%. 2 Reliability factors (SXRD): Rwp = 6.78%, Rp = 4.61%, RB = χ = 29.5%. This section provides a detailed structural analysis of the product based on combined Rietveld refinement of ND and SXRD data. Because no additional peaks or splitting of reflections were observed in the XRD pattern, structural refinement of the sample synthesized at 240 °C was performed assuming a single double-perovskite-type phase with a more symmetric space group (Im-3m, No. 229). For the joint data refinement, structural data for the reported 6 double-perovskite phase was used as the initial model. The structural model was deduced from the existence of Bi, Ba, K, and Na in nominal molar ratios (1:0.95:0.22:0.17), as detected by ICP. By taking into account the results of chemical analysis, subsequent combined refinements were performed based on ND and SXRD data. Both the synchrotron and neutron powder diffraction patterns suggest that the compound peaks could be indexed as an AʹAʹʹ3B4O12 doubleperovskite-type structure with a cubic Im-3m (No. 229) space group. The lattice parameter derived from SXRD and ND patterns is a = 8.52933(5) Å, which is slightly smaller than 6 that reported for the double perovskite. Initially, we freely refined the occupation factors of K, Na, Ba, and Bi based on previously reported (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12 structure. Free refinement at the Bi site based on combined refinement showed ~11% of Na incorporation onto Bi sites improved the fitting of both SXRD and ND; furthermore, K and Ba at Bi sites are unlikely because of their large ionic radii, and occupancies of K and Ba in the Aʹ and Aʹʹ sites, respectively, were refined. The refinement of the occupation of Ba in the Aʹʹ sites reached close to unity; thus, further refinement was performed at this fixed value. On the other hand, the A′ site could not be satisfactorily refined. Refinement of the K occupation suggested a small number of vacancies (~10%); furthermore, trials with Na and Ba reached comparable refinement factors. Although further refinement of the K occupancy was performed without modeling a vacancy (in consideration of the chemical analysis), we cannot rule out the possibility of incorporation of Ba and K and vacancies in A′ sites. No indication of oxygen deficiency was detected in the refinement. The final refinement was performed with a model in which the respective Aʹ and Aʹʹ sites are entirely occupied by K and Ba, whereas Bi and Na partial occupy the B sites (Bi/Na = 0.89/0.11). The Rietveld refinement fittings, crystallographic data, and structural parameters of this joint refinement are depicted in Figures 2(a) and (b) and Table 1. The composition and refinement parameters of these comparative models are listed in Table S1.

Page 4 of 8

The validity of space group Im-3m in this model was justified by refining the structure with similar space groups, such as Im-3 (No. 204) and I-43m (No. 217). Prediction of these space groups also produced similar vacancies on the Bi sites and comparable structural parameters, with somewhat higher R factors for the I-43m space group. Therefore, space group Im-3m appears to be appropriate for this refinement model. Moreover, the anti-site disordering was also checked by assuming that some K atoms occupy Na sites and vice versa; however, this did not leave to improvement in the refinement. However, we exclude the possibility that Ba0.6K0.4BiO3 is present with the lattice parameter equal to half of the double perovskite. This is because the composition change, assuming the small amount of incorporation of Ba0.6K0.4BiO3, improved the fitting of ND pattern. Notably, the occupation of Na and Bi on the same site is not a common phenomenon in perovskite oxides. Nonetheless, Na0.5Bi0.5TiO3 (BNT) is a perovskite-type oxide in which Na and Bi occupy close crystallographic positions, although detailed analysis indicates off-centering of Bi atoms 27 and on-centering of Na atoms in BNT. Furthermore, the refinement suggests that the (Bi/Na)O6 octahedra are slightly tilted at the corner of the structure and form a zigzag Bi–O– Bi bond. This is different from the results reported for Ba114-16 and the xKxBiO3 and Sr1-xKxBiO3 superconducting systems, zigzag bond breaks the Bi coordination symmetry. The sample prepared at 240 °C has a different coordination environment at two different types of A sites: the Ba–O bond distances at the 6b site is 3.016(5) Å, longer than the K–O bond at the 2a site, 2.942(5) Å. On the other hand, the shortest Bi/Na–O bond length (shown in Figure 1) is 2.1336(3) Å, which is the same for each neighboring octahedral oxygen. However, the shorter Bi–O bond distances are 2.11 and 2.1098(4) Å for the superconductive 14 15 perovskites Ba0.6K0.4BiO3 and Sr0.4K0.6BiO3, respectively. In the (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite, the octahedral framework is slightly tilted [∠Bi/Na–O–Bi/Na = 176.0(3)°] (Figure 1), which is an indication of structural 14 distortion as compared to the Ba0.63K0.37BiO3 structure. The compositional and structural homogeneity of the materials were examined by SEM and TEM. Overall, compositional homogeneity was confirmed by EDX mapping (Figure S3-4), and structural homogeneity was inferred from the similar dark-field images, which were taken using the superlattice 110 and 220 reflections (Figure S5). This indicates the homogeneity of the average structure of the double perovskite suggested by the dual SXRD and ND refinement. However, slight differences in K and Na mapping in the dark-field images within regions (on the scale of tens or hundreds of nm) were also seen. Although it is difficult to prove the existence of this inhomogeneity, nanodomains in the double perovskite with compositional and structural fluctuations might affect the smeared superconductive transitions, as described below; similar research about nanodomain structure have been reported in FeAs and FeSe 28-29 superconducors

4


Page 5 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The Rietveld refinement profiles and structural data for these compounds are shown in Figure S6 and Table S2. Table S3 summarizes the synthetic conditions, transition temperatures (Tc), and lattice parameters (a) for the samples synthesized from 220 to 240 °C and the selected bond lengths and/or bond angles based on ND data for the sample prepared at 240 °C. The structural parameters of the samples synthesized at 220, 230, and 240 °C showed broad similarities, but they had appreciable differences in their crystal structures, lattice parameters, and superconducting properties. Therefore, hydrothermal reaction temperature affects the crystallographic structures.

3.2 Effect of synthesis temperature on superconductivity Figure 3 reveals the magnetic susceptibility of the (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite synthesized at 240 °C. The inset shows an expanded view of Tc. A very clear diamagnetic superconducting signal is observed, with a transition to the superconducting state at ~31.5 K. The effect of the reaction temperature on the superconducting properties of double-perovskite bismuthates was also investigated. Figure 4 shows the temperature dependence of the magnetic susceptibility (4πM/H) curves for the samples synthesized at various reaction temperatures from 180 to 260 °C under ZFC conditions with H = 10 Oe. All the samples exhibited a diamagnetic superconducting signal. The mag superconducting transition temperatures (Tc ) and diamagnetic shielding volume fractions increased as the reaction temperature increased up to at 240 °C; a further mag increase of reaction temperature led to decrease of Tc and volume fraction, as shown in the insets of Figure 4. The sample synthesized at 240 °C exhibited the highest diamagnetic (shielding volume fraction ~110% at 3 K) mag of superconducting behavior, with an onset Tc approximately 31.5 K, which is higher than that previously 6 reported. This large volume fraction with higher Tc confirms the bulk superconducting nature of this double perovskite. However, the FC curve, which is related to a Meissner volume fraction of ~30% at 3 K (Figure 3); this deviation might be responsible for the vortex pinning in the FC measurement.

Figure 4. Magnetic susceptibility curves for the samples prepared at reaction temperatures of 180–260 °C in a magnetic field of 10 Oe in ZFC mode. The reaction temperature dependence of Tc and the diamagnetic shielding volume fraction are shown in the insets.

The temperature dependence of the electrical resistivity, ρ(T), was measured for the highest Tc (~31.5 K) for a sample pellet fabricated using a cubic-anvil-type high-pressure system (6 GPa/RT), as presented in Figure 5. The resistivity curve shows semi-metallic behavior in the normal-state onset region 300–28 K and dropped at ~28 K, referred to as Tc , mag (~31.5 K). The zero resistivity of the which is near Tc prepared sample was confirmed to be less than 13 K. However, the smeared transition, negative gradient of mag resistivity, and small difference (~3.5 K) between Tc and onset Tc are considered to indicate grain boundaries, compression, and/or nanodomain structures. A similar phenomenon was also observed in our previous study and 3,6,28,35 has been reported for some other superconductors. The onset zero (~28 K) and Tc (~13 K) in this report is magnitude of Tc higher and that of resistivity (mΩ cm) is smaller than that in 6 our previous report. Figure S7 shows the magnetic field dependence of superconducting behavior for the prepared sample at 240 °C under an external field from 0.1 to 1.9 T as measured using a standard four-probe terminal. With onset increasing magnetic field, Tc gradually decreased, but the superconducting behavior persisted up to the highest limit (1.9 T). This behavior demonstrates further evidence of bulk superconductivity and the properties of a type-II superconductor.

Figure 3. Temperature dependence of DC magnetic susceptibility for the hydrothermally synthesized (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 sample in an external field of 10 Oe in both ZFC and FC modes. The inset shows an expanded view of Tcmag at ~31.5 K.

5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 8

compression, or both. It can be seen from the partial DOS (Figure S10) that the s and p orbitals are strongly hybridized in the bands crossing EF, in agreement with the calculations 6 of (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12. The dispersion of conduction bands intersecting the Fermi level increased, which might be related to zigzag Bi–O–Bi bond. The dominant contribution to DOS at EF appears from the O-2p and Bi -6s and 6p orbitals, as observed from the partial DOS (Figure S10).

Figure 5. The characteristic change in electrical resistivity, ρ(T), of the (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 pellet sample. The inset shows a Tconset of ~28 K and a Tczero of ~13 K on an expanded scale.

3.3 Thermal behavior studies Figure S8 depicts the weight loss profile for the two compounds prepared hydrothermally at 240 and 220 °C. The TG curve of the sample synthesized at 240 °C exhibits a total mass loss of 1.0% from 500 to 700 °C; in contrast, the sample at 220 °C shows a somewhat earlier and greater mass loss, approximately 1.9% from 450 to 700 °C. This small deviation observed in the TG curves may be correlated to either oxygen deficiency or different chemical compositions, as discussed in this report. However, no significant mass change was found below 500 °C; therefore, the main mass loss was caused by oxygen evolution, accompanied by the reduction 5+ 3+ of Bi to Bi . Figure S9 shows the superconducting behavior of the sample at high temperatures; in contrast, at 400 °C, a mag slightly lower diamagnetic signal and Tc as compared to the as-prepared sample was observed. However, for the sample heated to 600 °C, a significant decrease in the onset temperature was observed, and, in the sample heated to 700 °C, the signal was lost. The aforementioned phenomenon may be caused by the phase transition from double perovskite to a simple perovskite structure and the loss of superconducting signal for the prepared sample. These structural changes from a double to a simple perovskite structure were also investigated by high-temperature SXRD 6 patterns. These results confirmed that the synthesized 25 single-phase double perovskite is different from both BKBO 36 and BPBO perovskite superconductors and that it can be prepared only by a hydrothermal reaction. 3.4 Electronic band structure To analyze the contributions and overlap of the conduction energy bands, we calculated the electronic band structure and DOS of (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite. The calculated energy bands of this compound revealed metallic properties, evident from the bands (colored lines) crossing the Fermi level, EF (Figure 6). On the other hand, the above mentioned resistivity results revealed semi6 metallic behavior similar to that previously reported. This inconsistency between experimental results and theoretical calculations might be attributed to grain boundaries,

Figure 6. The calculated band structure for (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite shows broad and nearly flat Bi-6s,6p and O-2p bands from the M to X and M to Γ points at EF. The total DOS is presented to the right of the figure.

The contribution of the O-2p orbital is greater in contrast to other orbitals, very similar to the reported simple- and 6,37,38 double-perovskite band structures. Importantly, the -2 total DOS at the EF in this report is 1.33 × 10 3 electrons/eV/Å , whereas the reproduced DOS value in the 6 -3 previously reported double perovskite was 9.27 × 10 3 electrons/eV/Å . This larger value of DOS might be responsible for the hybridization of Bi-6s orbitals in Bi–O 16 bond that resulted in flat bands at EF. Accordingly, the observed conduction bands formed from the Bi -6s,6p and O-2p orbitals are broader and flatter from points M to X and M to Γ in the vicinity of EF as compared to the 6 (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12 structure. The occurrence of broad and nearly flat bands with the formation of a saddle point at EF in Γ has been suggested as a favorable condition 16 to enhance electron pairing, and this may be the reason for the increase Tc in this study. However, superconducting behavior is also related to Bi valence in the samples synthesized from 180 to 260 °C. Our previous report revealed +4.39 +4.44 that the less-than-half filled Bi-6s at Bi and Bi generated maximum carriers for (Na0.25K0.45)(Ba1.00)3(Bi1.00)4O12 and Ba0.6K0.4BiO3 6,37 superconductors, respectively. A similar oxidation state of +4.41 Bi was found for (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double perovskite in the current study, where the maximum number of carriers were generated, confirming the metallic behavior and, thus, the high Tc of ~31.5 K. 4. Conclusions A new member of double-perovskite-type bismuthate was successfully synthesized via hydrothermal reaction at 240 °C. The crystal structure of (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 was analyzed by combined Rietveld refinement of neutron

6


Page 7 of 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diffraction and synchrotron XRD data and TEM analysis. The material was confirmed to contain ordered substitution of K and Ba atoms at the A sites of a double-perovskite-type structure. Combined Rietveld refinement of ND and SXRD data revealed mixed occupancy of Na and Bi atoms at some sites, and a good fit was obtained for refinement of these occupancies, and mixed occupancy influenced the superconductivity of the solid. The validity of the refined crystal structure was also confirmed from the electron diffraction patterns, which revealed a double supercell. The susceptibility and electrical resistivity measurement results showed that (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 exhibits a large superconducting volume fraction (~110%), with an onset of mag onset at ~31.5 K and Tc at ~28 K, respectively. Zero Tc resistivity of the compound was also confirmed below 13 K. Band structure calculations revealed that the hybridized Bi6s/6p and O-2p orbitals enhanced the DOS and the flatness of the conduction bands near EF, enhancing electron pairing and, therefore, leading to a higher transition temperature of superconductivity. For this double-perovskite compound, investigation of the thermal behavior revealed the structure is stable and superconductive up to 500 °C. Notable results on the structure showed Na incorporation and zigzag Bi–O– Bi bonding, which have not been previously reported in single Bi perovskites showing superconductivity. Further challenges remain in terms of improving Tc and in understanding the reasons behind the semi-metallic behavior in Bi-based double-perovskite superconductors.

ASSOCIATED CONTENT Supporting Information Crystallographic data of (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 (CIF) And tables of crystal data, details of structural analysis, electric and magnetic susceptibility curves, SEM and TEM images.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (N. Kumada). Phone: +81-55-220-8615. Fax: +81-55-254-3035.

Present address Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae-cho, Kofu 400-8511, Japan. Author Contributions N.K. conducted this research work in collaboration with M.A. and Y.K. M.H.K.R. prepared powder samples and performed laboratory XRD measurements. T.T., E.M., C.M., and Y.K. performed SXRD experiments. M.Y., K.F., J.R.H., and M.A. contributed to the neutron experiments. M.H.K.R., A.M., T.T., and N.K. performed the chemical analysis. M.H.K.R., A.M., and N.K. performed structural refinements with help from E.M., C.M., and Y.K. Magnetic measurements were performed by M.H.K.R., A.K., and N K. All the authors discussed the results; M.H.K.R. wrote the manuscript with comments from the co-authors.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT A.M. acknowledge Prof. Hiroshi Mizoguchi for discussions on the Bi–O bond. The synchrotron experiments were carried out at SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI: Proposal No. 2014A1008). The neutron powder diffraction measurements were performed with approval of Echidna: 2696, 3209. This research work was partially supported by JSPS KAKENHI Grant Number 26420678.

ABBREVIATIONS XRD, X-ray powder diffraction; SXRD, synchrotron X-ray diffraction; ND, neutron diffraction; BKBO, Ba1-xKxBiO3; BPBO, BaPbxBi1-xO3; ICP magnetic susceptibility; Tc, transition temperature; ZFC, zero-field cooling; FC, field cooling; SEM, scanning electron microscopy; TEM, transmission electron microscopy; BF, bright field; DF, dark field; TGA, thermogravimetric analysis; HAADF-STEM, highangle annular-dark-field scanning transmission electron microscopy.

REFERENCES (1) Baumert, B. A. J. Supercond. Barium potassium bismuth oxide: A review, 1995, 8, 175-181. (2) Jiang, H.; Kumada, N.; Yonesaki, Y.; Takei, T.; Kinomura, N., Hydrothermal synthesis of a new perovskite-type bismuth oxide: Ba0.96Bi0.86O2.59(OH)0.41, J. Ceram. Soc. Jpn. 2009, 117, 214216. (3) Rubel, M. H. K.; Takei, T.; Kumada, N.; Ali, M. M.; Miura, A.; Tadanaga, K.; Oka, K.; Azuma, M.; Magomae, E.; Moriyoshi, C.; Kuroiwa, Y., Hydrothermal synthesis of a new Bi-based (Ba0.82K0.18)(Bi0.53Pb0.47)O3 superconductor, J. Alloys Compd. 2015, 634, 208-214. (4) Jiang, H.; Kumada, N.; Yonesaki, Y.; Takei, T.; Kinomura, N.; Yashima, M.; Azuma, M.; Oka, K.; Shimakawa, Y., Hydrothermal Synthesis of a New Double Perovskite-Type Bismuthate, (Ba0.75K0.14H0.11)BiO3centerdotnH2O, Jpn. J. Appl. Phys. 2008, 48, 010216. (5) Cava, R. J.; Batlogg, B.; Krajewski, J. J.; Farrow, R.; Rupp, L. W.; White, A. E.; Short, K.; Peck, W. F.; Kometani, T. Superconductivity near 30 K without copper: the Ba0.6K0.4BiO3 perovskite, Nature 1988, 332, 814-816. (6) Rubel, M. H. K.; Miura, A.; Takei, T.; Kumada, N.; Ali, M. M.; Nagao, M.; Watauchi, S.; Tanaka, I.; Oka, K.; Azuma, M.; Magome, E.; Moriyoshi, C.; Kuroiwa, Y.; Azharul Islam, A. K. M., Superconducting double perovskite bismuth oxide prepared by a low-temperature hydrothermal reaction, Angew. Chem. Int. Ed. 2014, 53, 3599 -3603. (7) Bhalla, A. S.; Guo, R.; Roy, R. The perovskite structure – a review of its role in ceramic science and technology, Mater. Res. Innov. 2000, 4, 3. (8) Yamazoe, N.; Teraoka, Y. Oxidation catalysis of perovskites --relationships to bulk structure and composition (valency, defect, etc.)Catal. Today, 1990, 8, 175-199. (9) Tejuca, L. G.; Fierro, J. L. G. Properties and Applications of Perovskite Type Oxides, Marcel Dekker, NY, 1993. (10) Martınez-Lope, M. J.; Alonso, J. A.; Casais, M. T. Synthesis, Crystal and Magnetic Structure of the New Double Perovskite Ba2MnMoO6, Z. Naturforsch, 2003, 58b, 571-576. (11) Hong, K. P.; Choi, Y. H.; Kwon, Y. N.; Jung, D. Y.; Lee, C. H. Atomic and Magnetic Long-Range Orderings in BaLaMRuO6 (M=Mg and Zn), J. Solid State Chem. 2000, 150, 383-390. (12) Ganguli, A. K.; Grover, V; Thirumal, M. New double perovskites having low dielectric loss: LaBaZnTaO6, LaSrZnNbO6 and Ba2Zn0.5Ti0.5TaO6, Mater. Res. Bull. 2001, 36, 1967.

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(13) Zhang, G.; Li, G.; Huang, F.; Liao, F.; Li, K.; Wang, Y.; Lin, J. Hydrothermal Synthesis of Superconductors Ba1-xKxBiO3 and Double Perovskites Ba1-xKxBi1-yNayO3, J. Alloys Compd. 2011, 509, 9804-9808. (14) Antipov, E. V.; Khasanova, N. R.; Psshirkov, J. S.; Putilin, S. N.; Bougerol, L. C. O.; Van Tendeloo, I. G.; Baranov, A. N.; Park, Y. W. The Superconducting Bismuth-Based Mixed Oxides, J. Low Temperature Phys. 2003, 131, 575-587. (15) Psshirkov, J. S.; Kazakov, S. M.; Abakumov, A. M.; Putilin, S. N.; Antipov, E. V. Synthesis and Characterization of New Phases: Sr3.75K1.75Bi3O12 and Sr3.1Na2.9Bi3O12, J. Solid State Chem. 2000, 152, 492-502. (16) Simon, A. Supraleitung und Chemie [Superconductivity and Chemistry], Angew. Chem. Int. Ed. Engl. 1997, 36, 1788-1806. (17) Liss, K. D.; Hunter, B.; Hagen, M.; Noakes, T.; Kennedy, S. Echidna—the new high-resolution powder diffractometer being built at OPALO, Phys. B 2006, 385, 1010-1012. (18) Rodringuez-Carvajal, Recent advances in magnetic structure determination by neutron powder diffraction, J. Phys. B 1993, 192, 55-69. (19) Momma, K.; Izumi, F. VESTA: a three-dimensional visualization system for electronic and structural analysis, J. Appl. Crystallogr. 2008, 41, 653-658. (20) Clark, S. J.; Segall, M. D.; Pickard, C. J.; Hasnip, P. J.; Probert, M. I. J.; Refson, K.; Payne, M. C., First principles methods using CASTEP, Z. Kristallogr. 2005, 220, 56 -570. (21) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple, Phys. Rev. Lett. 1996, 77, 38653868. (22) Chaillout, C.; Durr, J.; Escribe-Filippini, C.; Fournier, T.; Marcus, J.; Marezio, M. Structure determination of a new perovskite phase in the Ba K - Bi - Na - O system, J. Solid State Chem. 1991, 93, 63-68. (23) Subramanian, M. A. Ordered Perovskites Containing Pentavalent Bismuth: Ba(Bi0.75M0.25)O3 and Ba(Bi0.67M0.33)O3, J. Solid State Chem. 1994, 111, 134-140. (24) Kumada, N.; Miura, A.; Takei, T.; Nishimoto, S.; Kameshima, Y.; Miyake, M.; Kuroiwa, Y.; Moriyoshi, C. Hydrothermal synthesis and crystal structure analysis of two new cadmium bismuthates, CdBi 2 O 6 and Cd 0.37 Bi 0.63 O 1.79, J. Asian Ceram. Soc. 2015, 3, 251–254. (25) Idemoto, Y.; Iwata,Y.; Fueki, K. Oxygen content and Tc of Ba0.6K0.4BiO3-δ, Phys. C 1992, 201, 43-49. (26) Hinks, D. G.; Dabrowski, B.; Jorgensen, J. D.; Mitchell, A. W.; Richards, D. R.; Pei, S.; Shi, D. Synthesis, structure and superconductivity in the Ba1−xKxBiO3−y system, Nature 1988, 333, 836-838. (27) Moriyoshi, C; Takeda, S; Kuroiwa, Y; Goto, M. Off-centering of a Bi ion in cubic phase of (Bi1/2Na1/2)TiO3, Jpn. J. Appl. Phys. 2014, 53, 09 PD 01-04. (28) Park, J. T.; Inosov, D. S.; Niedermayer, C.; Sun, G. L.; Haug, D.; Christensen, N. B.; Dinnebier, R.; Boris, A. V.; Drew, A. J.; Schulz, L.; Shapoval, T.; Wolff, U.; Neu, V.; Yang, X.; Lin, C. T.; Keimer, B.; Hinkov, V., Electronic Phase Separation in the Slightly Underdoped Iron Pnictide Superconductor, Phys Rev Lett 2009, 102 (11), 117006. (29) Ricci, A.; Poccia, N.; Campi, G.; Joseph, B.; Arrighetti, G.; Barba, L.; Reynolds, M.; Burghammer, M.; Takeya, H.; Mizuguchi, Y.; Takano, Y.; Colapietro, M.; Saini, N. L.; Bianconi, A., Electronic Phase Separation in the Slightly Underdoped Iron Pnictide Superconductor Ba1−xKxFe2As2, Phys Rev B 2011, 84 (6). (30) Ekimov, E. A.; Sidorov, V. A.; Bauer, E. D.; Mel'nik, N. N.; Curro, N. J.; Thompson, J. D.; Stishov, S. M. Superconductivity in diamond, Nature 2004, 428, 542-545. (31) Takano,Y.; Nagao, M.; Sakaguchi, I.; Tachik, M.; Hatano, T.; Kobayashi, K.; Umezawa, H.; Kawarada, H. Superconductivity in diamond thin films well above liquid helium temperature, Appl. Phys. Lett. 2004, 85, 2851-2853.

Page 8 of 8

(32) Yamanaka, S.; Hotehama, K.; Kawaji, H. Superconductivity at 25.5 K in electron-doped layered hafnium nitride, Nature, 1998, 392, 580-582. (33) Kawaji, H.; Hotehama, K.; Yamanaka, S. Superconductivity of Alkali Metal Intercalated β-Zirconium Nitride Chloride, AxZrNCl (A = Li, Na, K), Chem. Mater. 1997, 9, 2127–2130. (34) Ito, T.; Fudamoto, Y.; Fukaya, A.; Gat-Malureanu, I. M.; Larkin, M. I.; Russo, P. L.; Savici, A.; Uemura, Y. J.; Groves, K.; Breslow, R.; Hotehama, K.; Yamanaka, S.; Kyriakou, P.; Rovers, M.; Luke, G. M.; Kojima, K. M. Two-dimensional nature of superconductivity in the intercalated layered systems LixHfNCl and LixZrNCl: Muon spin relaxation and magnetization measurements, Phys. Rev. B 2004, 69, 134522- 134534. (35) Zhang, S.; Tanaka, M.; Watanabe, E.; Zhu, H.; Inumaru, K.; Yamanaka, S. Superconductivity of alkali metal intercalated TiNBr with α-type nitride layers, Supercond. Sci. Technol. 2013, 26, 122001 (7pp). (36) Marx, D. T.; Radaelli, P. G.; Jorgensen, J. D.; Hitterman, R. L.; Hinks, D. G.; Shiyou P.; Dabrowski, B. Metastable behavior of the superconducting phase in the BaBi1-xPbxO3 system, Phys. Rev. B 1992, 46, 1144-1156. (37) Jung, D.; Choi, E.-K. Differences of structural and electronic properties in Ba(1-x)K(x)BiO3 (x=0, 0.04, and 0.4), Bull. Korean. Chem. Soc. 1999, 20, 1045-1048. (38) Meregalli, V.; Savrasov, Electron-phonon coupling and properties of doped BaBiO3. S. Y. Phys. Rev. B 1998, 57, 1445314469.

Table of Contents (TOC)

8


Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a

Recommend Documents