Barium Potassium Bismuth Oxide Synthesis and Physical Properties (original) (raw)
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Effects of La- and Pr-Substitution on the Structure and Superconductivity of Ba0.6K0.4BiO3
Rare Metal Materials and Engineering, 2015
Two compositional series based on Ba0.6-yLayK0.4BiO3 and Ba0.6-zPrzK0.4BiO3, with y and z being 0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, were synthesized using a molten salt method. X-ray powder diffraction data reveal that the initially undoped cubic crystal symmetry expands slightly to orthorhombic with Pr substitution but not with La substitution. A linearly reduction of the pseudo-lattice parameter following ap=4.28257-0.02469y (0.025≤y≤0.4) can be observed in Ba0.6-yLayK0.4BiO3. A systematic decrease of the transition temperature, Tc, is clarified by magnetic measurements and the superconductivity is finally vanished at y, z = 0.2 owing to the distortion of the crystal structure and the disproportionations of bismuth valence.
Role of barium addition on the properties of bismuth-based superconductors
Journal of Materials Science, 1992
The effect of the addition of barium on the zero resistance temperature, Tc, of Bil.6Pbo.4Srl.eCazBaxCu4Ov, x = 0.4, 0.5, 0.6, 0.8 and 1.6 was studied. The added barium had the effect of raising T c to a higher temperature region, although too much barium gave rise to semiconducting resistance temperature behaviour. X-ray diffraction analysis showed that as the barium concentration, x, increased from 0.4 to 0.8, a decrease in the low T c phase and peaks due to CuO and BaBiO3 appeared, whereas an increase in the peaks due to the high T c phase and BaCu02 were seen. Critical current densities were also measured in zero field at 77 K.
Soviet Physics Uspekhi, 1986
This article reviews the experimental and theoretical investigations of the superconducting solid solutions BaPb1-x BixO3 (BPB), which have critical temperatures Tc ~ 13 K. The crystal structure, structural phase transitions, and the electrical and optical properties are examined in detail. Methods of preparing ceramic samples, as well as thin films and single crystals, are discussed briefly. Measurements of the electron specific heat and of the upper critical magnetic field are interpreted in terms of a theory of superconductors with partial dielectrization of the electron spectrum. Particular attention is paid to those properties of BPB which are a consequence of the granularity of the ceramic macrostructure and the existence of weak Josephson links between the granules. Correlations between the composition dependences of various normal and superconducting characteristics of BPB are elucidated, and the nature of the superconducting high Tc state with a small electron density of states (N(0) = 3-1021 eV-1 cm- 3 ) at the Fermi surface is discussed.
Effect of growth conditions on the superconductivity of Ba1−xKxBiO3 crystals
Physica C: Superconductivity, 1993
The effects of growth conditions on the superconductivity of Bal_xKxBiO3 (BKBO) crystals grown electrochemically have been studied. Magnetic and resistive measurements reveal that the superconductivity of BKBO crystals depends strongly on the synthesis temperature, applied voltage and current, and synthesis time. The electron-phonon coupling parameter (2vh) estimated from critical field parameters of a single crystal (To= 30 K) suggests a phonon-mediated mechanism for superconductivity in BKBO.
Valency states of Bi in BaPb1−xBixO3−δ and Ba1−xKxBiO3−δ superconducting oxide
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1995
X-ray absorption measurements have been made above the L,-Bi(Pb) edges in Bi-based three-dimensional superconductive oxides: BaPb,_,Bi,O, (x=0, 0.25, 1; 810.2) and Ba,-,K,BiO,_, (x=0.4; 810.2). The Bi valence state as a crucial parameter for understanding superconductive properties of these oxides has been determined from XANES spectra analysis. It was found that in spite of similar Bi and Pb near-edge structures the oxygen deficiency leads to a change in the L,-Bi edge both for BaPbBiO and for BaKBiO while the Pb edge practically does not change for BaPbBiO. The character of the changes observed and the interpretation of the NES spectra carried out by calculation give us the opportunity to confirm that the Bi valence state differs from the Pb one. The disproportionality of Bi4+ on two different Bi valence states takes place for both compounds, but in addition to Bi3+ the second valence state is not exactly Bi", as it was considered earlier, but Bi3+L)', n = l-2. The results obtained give evidence of a local CDW increase with oxygen deficiency for both compounds.
Superconducting energy gap and a normal-state excitation in Ba0.6K0.4BiO3
Physical review. B, Condensed matter, 1989
We report the first measurement of the energy gap of the high-temperature bismuth oxide superconductor Ba06K0&BiO3 (T, =30 K). With temperatureand magnetic-field-dependent infrared reflectivity measurements, we obtain a reduced energy gap of 2h/kT, =3.5+0.5, consistent with a BCS-type mechanism with moderate or weak coupling. In the normal state a broad peak in the infrared conductivity is observed near 5000 cm '. This unusual infrared behavior is common to both the BaPbl "Bi 03 and the Bal K Bi03 systems and may provide a fundamental clue to the mechanism of superconductivity in the cubic bismuth oxides.
Local lattice distortions and the nature of superconductivity in Ba(K)BiO[sub 3]-BaPb(Bi)O[sub 3]
AIP Conference Proceedings, 2001
We propose a new scenario for the metal-insulator phase transition and superconductivity in the perovskite-like bismuthates Ba 1 -x K x BiO 3 (BKBO) based on our EXAFS studies. We show that two types of charge carriers, the local pairs (real-space bosons) and the itinerant electrons, exist in the metallic compound Ba 1 -x K x BiO 3 ( x ≥ 0.37). The real-space bosons are responsible for the charge transport in semiconducting BaBiO 3 and for superconductivity in the metallic BKBO. The appearance of the Fermi liquid state as the percolation threshold is overcome ( x ≥ 0.37) explains the observed metal-insulator phase transition. Because bosons and fermions occupy different types of the octahedral BiO 6 complexes, they are separated in real space, and therefore, the spatially separated Fermi-Bose mixture of a new type is likely to be realized in the bismuthates. The nature of superconductivity is consistently explained in the framework of this scenario. A new superconducting oxide Ba 1 -x La x PbO 3 has been successfully synthesized to check our conclusions. © 2001 MAIK "Nauka/Interperiodica".
Physica C: Superconductivity, 1996
X-ray absorption spectroscopy (XAS) measurements at the PbL 3 and BiL 3 edges have been made for Bi-based perovskite oxides: BaPb l_~BixO 3_ ~ (x = 0, t5 < 0.2; x = 0.25, t~ < 0.15; x = 1, 8 < 0.4) and Ba0.6K0.4BiO3 -8 (t5 < 0.2). Oxygen reduction leads to larger changes in the BiL 3 edge of BaPb~ _xBixO3_ 8 (x = 0.25, 1.0) and Bao.6K0.4BiO3_ 8 than in the PbL 3 edge of BaPbl_~BixO3_ 8 (x= 0, 0.25). Single-electron calculations of the X-ray absorption near-edge structure (XANES) spectra in BaBiO 3 _ 8 and BaPbO 3 _ ~ could not predict a different behaviour of the Bi L 3 and the Pb L 3 edges under oxygen reduction. This may be explained by assuming many-body states in the electronic structure of the Bi-O complexes. Extended X-ray absorption fine structure (EXAFS) measurements indicate a very small increase of the single Pb-O bond length with ~ in BaPb~ _xBixO3_ 8 ( x = 0, 0.25). On the other hand, the separation between two different Bi-O bond lengths increases with 8 in BaPbl_xBixO3_~ (x~0.25, 1). Two Bi-O distances, separated by 0.07 A, could be distinguished for Bao.6Ko.aBiO3_8 in the semiconducting phase (8>0.2). The superconductivity destruction in BaPbo.75Bio.2503_ ~ and Ba0.6K0.4BiO3_ 8 upon oxygen reduction is mainly accompanied by changes in the electronic and local structures of the Bi-O complexes. The results were employed to test some models of charge disproportionation in BaPbBiO and BaKBiO. Neither the Bi3++ Bi 5÷ model nor the model of charge ordering on Bi-O bonds with normal bismuth states (Bi 4÷-+ a) have been directly supported by the XAS data. As an alternative, we have proposed a charge disproportionation model in the form: 2Bi4+~ Bi3++ Bi3+L 2, where L 2 denotes two holes spread on 2p orbitals of six oxygen atoms surrounding the Bi ion. This model is in agreement with the X-ray absorption, photoelectron spectroscopy, muon spin rotation and structural experiments on BaPbBiO and BaKBiO.
Chemistry of Materials, 1993
Cyclic voltammetry has been used to investigate the electrodeposition of the superconducting material, Bal,K,Bi03. Reactions occurring at a Pt substrate electrode over a wide potential range have been assigned. Evidence has been found for time-dependent (cycle number) electrochemical behavior. High-quality superconducting crystals can be obtained only when the potential of the electrode is held in the region of predominantly kinetic control. The to BiV oxidation appears as two peaks during the anodic scan. Reproducible cyclic voltammograms were obtained only after the KOH flux containing Ba(OH)2 and Biz03 was equilibrated for 24 h under a water-saturated argon atmosphere. High-quality superconductive crystals are obtained only when the deposition potential is on the rising portion of the Bin' to BiIV oxidation peak.
Superconductivity in the BaPb1−xBix/2Sbx/2O3 system
Physica C: Superconductivity, 1998
The system BaPb Bi Sb O has been synthesized and investigated. The parent compound, BaBi Sb O , is a 1yx xr2 x r2 3 0.5 0.5 3 rhombohedral perovskite, having an ordered arrangement of Bi 3q and Sb 5q ions. Upon Pb-doping the ordered arrangement vanishes at x f 0.60, but the system remains insulating. Superconductivity occurs in the composition range of about Ž. 0.2 F x-0.4 with the T magnetically determined ranging from 2 K to 6 K. The most important feature of this system is c that the Bi exists only as Bi 3q. Therefore, the occurrence of superconductivity may shed the light on whether the pairing mechanism in the bismuthate superconductors can be described in terms of local pairs.