Co-appearance of superconductivity and ferromagnetism in a Ca2_2RuO4_4 nanofilm crystal

By tuning the physical and chemical pressures of layered perovskite materials we can realize the quantum states of both superconductors and insulators. By reducing the thickness of a layered crystal to a nanometer level, a nanofilm crystal can provide novel quantum states that have not previously been found in bulk crystals. Here we report the realization of high-temperature superconductivity in Ca$_2$RuO$_4$ nanofilm single crystals. Ca$_2$RuO$_4$ thin film with the highest transition temperature $T_c$ (midpoint) of 64~K exhibits zero resistance in electric transport measurements. The superconducting critical current exhibited a logarithmic dependence on temperature and was enhanced by an external magnetic field. Magnetic measurements revealed a ferromagnetic transition at 180~K and diamagnetic magnetization due to superconductivity. Our results suggest the co-appearance of superconductivity and ferromagnetism in Ca$_2$RuO$_4$ nanofilm crystals. We also found that the induced bias current and the tuned film thickness caused a superconductor-insulator transition. The fabrication of micro-nanocrystals made of layered material enables us to discuss rich superconducting phenomena in ruthenates

Oxygen Separation Performance of Ca2AlMnO5+delta as an Oxygen Storage Material for High-Temperature Pressure Swing Adsorption

High-temperature pressure swing adsorption (HT-PSA) is a promising energy-saving approach for oxygen production from air. Ca2AlMnO5+delta, a Brownmillerite-type perovskite, is a promising sorbent for HT-PSA because of its remarkably high oxygen storage capacity (up to 3.3 wt%). In this study, we investigated the redox thermodynamics of Ca2AlMnO5+delta by pressure-composition-temperature (PCT) measurements and investigated the HT-PSA performance of Ca2AlMnO5+delta pellets in a 100 g-scale packed-bed-type reactor. PCT measurements revealed that Ca2AlMnO5+delta can reversibly separate 2.2 wt% of oxygen per cycle under equilibrium conditions between ambient oxygen partial pressure and 5x10-4 MPa at 525 degrees C. However, in a 5 min switching HT-PSA test, Ca2AlMnO5+delta pellets were able to reversibly separate less than 1 wt% oxygen per cycle, which is significantly lower than that estimated from the thermodynamic properties of Ca2AlMnO5+delta. On the other hand, the exothermic oxygen storage and endothermic oxygen release reactions cause significant temperature variation of the packed bed. This study clarifies that, in order to increase the energy efficiency of oxygen separation by HT-PSA, there is a need to compensate for the heat of reaction, which changes the reactor temperature in a direction that interferes with the reaction