SPring-8, the large synchrotron radiation facility

Release Date

03 Mar, 2014

University of Yamanashi
Hiroshima University
Tokyo Institute of Technology

Topic
• A new superconducting double perovskite bismuth oxide, (Na_0.25K_0.45)(Ba_1.00)₃(Bi_1.00)₄O₁₂, was discovered.
• This is the first example of an A-site ordered double perovskite structure with superconductive properties.
• This discovery provides a guiding principle for the exploration of new high-temperature superconductors, and an increased understanding of the mechanisms of superconductivity.

Although the superconductor⁽²⁾ is an important functional material for maglev propulsion systems and MRI techniques, it requires a considerable amount of energy for cooling, which is essential for the occurrence of the superconductivity phenomenon. Many types of superconductive materials have been developed to overcome the cooling requirement, including Cu-based, Bi-based, and Fe-based superconductors. Moreover, the superconductive mechanism in high-temperature superconductive materials is an important but unsolved scientific problem.

This new bismuth oxide material was synthesized via a hydrothermal method⁽³⁾, which has been used for the syntheses of quartz, nanoparticles, and ceramics. The material formed a perovskite-type structure consisting of sodium, potassium, barium, bismuth, and oxygen, and its superconducting transition was confirmed at 27 K. Zero resistivity⁽⁴⁾ was confirmed in the pressed pellet form. Electron diffraction and synchrotron X-ray diffraction⁽⁵⁾ analyses revealed that the material did not have a commonly reported simple perovskite structure, but it exhibited an A-site ordered double perovskite structure with a longer range ordering. In this structure, the A site in ABO₃ perovskite oxide splits into two A sites, which K/Na and Ba respectively occupy. Recently, A-site ordered double perovskite structures have attracted much attention for their potential applications as various functional materials for magnetoresistance⁽⁶⁾ and negative thermal expansion⁽⁷⁾, and our research represents the first example of a double perovskite oxide with superconductive properties. The other advantages of this material are that the material can be synthesized at lower temperatures, and it consists of less toxic elements.

Although the superconducting transition temperature of this material is still relatively low, we expect that adjustments in the structure and composition will result in an increase in the transition temperature. This finding also allows us to further explore the relationship between superconductivity and long-range ordering, and provides a new guideline for exploring high-temperature superconductors.

This research was performed by following collaborators: Mirza H. K. Rubel, Akira Miura, Takahiro Takei, M. Mozahar Ali, Masanori Nagao, Satoshi Watauchi (Yamanshi University), Kengo Oka (Tokyo Institute of Technology), Eisuke Magome, Chikako Moriyoshi (Hiroshima University).

<<Figures>>

<<Glossary>>
1 Perovskite Structure
A common crystallographic structure of oxides, formulated as ABO₃. An A-site ordered structure, as discovered in this research, has two kinds of A sites and is formulated as A’A’’₃B₄O₁₂.

2 Superconductivity
Zero resistivity below a critical temperature, Tc. Extensive research has been performed not only to investigate the basic science, but also to develop many applications of superconductivity.

3 Hydrothermal synthesis
A synthesis method under high-pressure water, which has been used for the synthesis of quartz crystals, nanoparticles, and ceramic powders.

4 Zero resistivity
No electrical resistivity, which is a characteristic of superconductors.

5 Synchrotron X-ray diffraction
An analytical method to examine crystal structures. The intensity and angle of synchrotron X-rays applied to the sample allow us to determine information regarding the crystal structures, including atomic order and bonding length. This research was performed using Beamline BL02B2 at the Spring-8 synchrotron radiation facility.

6 Magnetoresistance
Electrical resistivity change due to external magnetic fields.

7 Negative thermal expansion
Thermal shrinkage with increasing temperature.