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In anti-ThCr2Si2-type Y2O2Bi with a Bi square net, the superconducting transition temperature (Tc) is scaled by unit cell tetragonality (c/a) via not only O intercalation but also H/F substitution and Li intercalation.

A new topotactic oxidation was developed using the solid-state oxidant Zr-doped CeO2. For the anti-ThCr2Si2 type Y2O2Bi, which became superconducting via oxygen intercalation during solid-state oxidation at 1000 °C, the topotactic oxidation enabled not only the oxygen intercalation at a much lower temperature of 200 °C, hampering the segregation of impurity phases, but also the highest superconducting transition temperature for Y2O2Bi.

YH2 (111) epitaxial thin films with two and four rotational crystal domains were directly grown both on CaF2 (111) and (001) substrates, respectively, at various growth temperature by reactive magn...

We report electrical transport properties and electronic structure of a nonmagnetic metal ${\mathrm{Cu}}_{2}\mathrm{Sb}$ single crystal. ${\mathrm{Cu}}_{2}\mathrm{Sb}$ was found to be a compensated metal with high carrier density $\ensuremath{\sim}{10}^{22}\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$ and high carrier mobility $\ensuremath{\ge}{10}^{3}\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{Vs}$ for both electron and hole carriers. The current-in-plane magnetoresistance at 2 K and 9 T was 730%, while the current-perpendicular-to-plane magnetoresistance at 2 K and 9 T was 2700% without the saturation. Angle-resolved photoemission spectroscopy throughout the three-dimensional (3D) bulk Brillouin zone signified a quasi-two-dimensional (2D) electron pocket axially centered along the M-A line and a 3D hole pocket at the \ensuremath{\Gamma} point, in accordance with the electron-hole compensated nature. The presence of quasi-2D open Fermi surface, in line with the first-principles band-structure calculations, is likely responsible for the observed nonsaturating current-in-plane magnetoresistance. The present result lays the foundation for realizing large magnetoresistance via Fermiology engineering in compensated metals.

Metallic anti-ThCr

Solid-state lithium (Li) batteries using spinel-oxide electrode materials such as LiNi0.5Mn1.5O4 are promising power supplies for mobile devices and electric vehicles. Here, we demonstrate stable b...

Metallic anti-ThCr$_2$Si$_2$-type $RE_2$O$_2$Bi ($RE$ = rare earth) with Bi square nets show superconductivity while insulating La$_2$O$_2$Bi shows high hole mobility, by expanding the c-axis length through oxygen intercalation. In this study, alkaline earth metal oxides (CaO, SrO, and BaO) were co-sintered with La$_2$O$_2$Bi. CaO and BaO served as oxygen intercalants without incorporation of Ca and Ba in La$_2$O$_2$Bi. On the other hand, SrO served as not only oxygen intercalant but also hole dopant via Sr substitution with La in La$_2$O$_2$Bi. The oxygen intercalation and hole doping resulted in expansion of the c-axis length, contributing to improved electrical conduction. In addition, the hole mobility was enhanced up to 150 cm$^2$V$^{-1}$s$^{-1}$ in La$_2$O$_2$Bi, which almost doubles the mobility in previous study.

Anti-ThCr$_2$Si$_2$ type $RE_2$O$_2$Sb ($RE$ = rare earth) with Sb square net has shown insulating conduction so far. Here we report the synthesis of La$_2$O$_2$Sb epitaxial thin films for the first time by multilayer solid-phase epitaxy. The valence state of Sb was about -2 evaluated from X-ray photoemission spectroscopy measurement, and the indirect band gap of 0.17 eV was observed. The La$_2$O$_2$Sb epitaxial thin film showed unexpectedly high electrical conduction as a narrow gap semiconductor, whose resistivity at room temperature was approximately ten-thousand-fold lower than that of La$_2$O$_2$Sb bulk polycrystal, attributed to increased carrier mobility probably due to suppressed Sb dimerization.

We report a series of layered superconductors, anti-ThCr$_2$Si$_2$-type $RE_2$O$_2$Bi ($RE$ = rare earth), composed of electrically conductive Bi square nets and magnetic insulating $RE_2$O$_2$ layers. The superconductivity was induced by separating Bi square nets as a result of excess oxygen incorporation, irrespective of the presence of magnetic ordering in $RE_2$O$_2$ layers. Intriguingly, the transition temperature of all $RE_2$O$_2$Bi including nonmagnetic Y$_2$O$_2$Bi was approximately scaled by the unit cell tetragonality ($c$/$a$), implying a key role of relative separation of the Bi square nets to induce the superconductivity.

We report a series of layered superconductors, anti-ThCr

Using synchrotron surface X-ray diffraction, we investigated the atomic structures of the interfaces of a solid electrolyte (Li3PO4) and electrode (LiCoO2). We prepared two types of interfaces with high and low interface resistances; the low-resistance interface exhibited a flat and well-ordered atomic arrangement at the electrode surface, whereas the high-resistance interface showed a disordered interface. These results indicate that the crystallinity of LiCoO2 at the interface has a significant impact on interface resistance. Furthermore, we reveal that the migration of Li ions along the interface and into grain boundaries and antiphase domain boundaries is a critical factor reducing interface resistance.

Recently, superconductivity was induced by expanding interlayer distance between Bi square nets in anti-ThCr2Si2-type Y2O2Bi through incorporation of excess oxygen with increased nominal amount of ...

Solid-state Li batteries containing Li(Ni0.5Mn1.5)O4 as a 5 V-class positive electrode are expected to revolutionize mobile devices and electric vehicles. However, practical applications of such batteries are hampered by the high resistance at their solid electrolyte/electrode interfaces. Here, we achieved an extremely low electrolyte/electrode interface resistance of 7.6 Ω cm2 in solid-state Li batteries with Li(Ni0.5Mn1.5)O4. Furthermore, we observed spontaneous migration of Li ions from the solid electrolyte to the positive electrode after the formation of the electrolyte/electrode interface. Finally, we demonstrated stable fast charging and discharging of the solid-state Li batteries at a current density of 14 mA/cm2. These results provide a solid foundation to understand and fabricate low-resistance electrolyte/electrode interfaces.

We here report the self-assembly of Li 3 Ni 2 NbO 6 (LNNO) epitaxial disks with very low height/width aspect ratios. An epitaxial LNNO thin film is obtained at a substrate temperature ( T s ) of 400 °C, using a pulsed laser deposition technique, and by increasing the T s to 600 °C, Li 3 NbO 4 epitaxial domains are formed inside the LNNO epitaxial film. Further increasing the T s to 700 °C leads to the formation of LNNO disks (with diameters of a few micrometers and a typical height of ~ 100 nm) embedded in a Li 3 NbO 4 film. Interestingly, transmission electron microscopy observations reveal that the LNNO disks are separated from the Li 3 NbO 4 films by amorphous compounds, indicating the formation of a planar core-shell structure. Understanding of the growth processes of these unique nanostructures pave the way to fabrication of higher hierarchical structures embedded in thin film matrices.

Anti-ThCr2Si2-type RE2O2Bi (RE = rare earth) with a Bi square net is known to show an insulator–metal transition by substituting RE. In this study, La2O2Bi polycrystals with different oxygen nonstoichiometry were synthesized. As the amount of oxygen in La2O2Bi increased, the c-axis length was expanded due to the generation of an additional 4e site for excess oxygen, while the a-axis length remained almost constant, indicating the separation of Bi square nets by oxygen intercalation. Concomitantly, transformation of insulating La2O2Bi into metallic La2O2Bi occurred with the change in carrier polarity from the n- to p-type. Despite its polycrystalline form, La2O2Bi with the largest amount of oxygen showed a rather high hole mobility of 85 cm2 V−1 s−1 among other layered oxypnictides and oxychalcogenides.

Solid-state Li batteries that use spinel LiNi0.5Mn1.5O4 as a positive electrode are promising energy-storage devices for portable electronics and electric vehicles. For practical applications of su...

Recently, superconductivity was induced by expanding interlayer distance between Bi square nets in anti-ThCr

Solid-state Li batteries containing Li(Ni

In this study, magnetization and neutron diffraction of anti-ThCr2Si2-type Tb2O2Bi polycrystals were measured at various temperatures. The magnetization cusp at 11.1 K was confirmed to correspond to antiferromagnetic ordering with a propagation vector of [0.5 0.5 0]. In addition, a metamagnetic behavior was observed below 5.0 K. The metamagnetic behavior could be attributed to the incommensurate magnetic structure with an anomaly at 5.0 K.

We prepared a nonvolatile memory device that could be reversibly switched between a high and a low open-circuit voltage (Voc) regime. The device is composed of a solid electrolyte Li3PO4 film sandwiched between metal Li and Au electrodes: a Li/Li3PO4/Au heterostructure, which was fabricated at room temperature on a glass substrate. The bistable states at Voc ∼ 0.7 and ∼0.3 V could be reversibly switched by applying an external voltage of 2.0 and 0.18 V, respectively. The formation and deformation of an ultrathin Au–Li alloy at the Li3PO4/Au electrode interface were the origin of the reversible switching.

All-solid-state lithium batteries with improved safety and larger capacity have been anticipated as a next-generation rechargeable battery. In particular, 5 V-class cathode material, LiNi0.5Mn1.5O4 (LNMO), has received considerable attention for the expected high power density. In all-solid-state LBs using LNMO, however, high interface resistance between an electrode and electrolyte hinders high power density. Thus, the reduction of the interface resistance and the investigation of the origins are of important issues. Recent progress in thin-film deposition techniques of electrodes and electrolytes has made it possible to fabricate all-solid-state thin film batteries with atomically controlled interfaces, and quantitative studies of the interface resistance values have been reported. In this study, we fabricated all-solid-state thin-film lithium batteries using LNMO epitaxial thin films and Li3PO4 solid electrolyte, and demonstrated a very low Li3PO4/LNMO interface resistance. Figure 1 shows a structure of all-solid-state thin films battery (inset), and its charge and discharge curves. The fabricated thin film batteries consisted of an epitaxial cathode LNMO(100) film, an amorphous solid-electrolyte Li3PO4 film, a metallic anode Li film, a current collector LaNiO3(100) film, and Nb-doped SrTiO3(100) substrate. To ensure a clean Li3PO4/LNMO interface in the thin films batteries, the ultrahigh vacuum chambers used for the film depositions and characterizations were all directly connected each other. The LNMO thin-film battery exhibits good battery performance. The charge and discharge curves show redox reactions of LNMO (Ni2+/Ni4+ and Mn3+/Mn4+), and the capacity did not degrade even up to the 100th cycle. We also evaluated the interface resistance using impedance spectroscopy, and found a very low interface resistance of ~5 Ωcm2. A Nyquist plot (Fig. 2) displays one semicircle at a higher frequency region (104~106 Hz), originating from the resistance of Li3PO4 (5×10-7 S/cm). In addition, a smaller semicircle at a lower frequency region (102~104 Hz) is attributed to the interface resistance at the Li3PO4/LNMO interface. The very low interface resistance of ~5 Ωcm2 is one order of magnitude smaller than those reported before, and implies that space charge layer formed at the Li3PO4/LNMO interface hardly results in high interface resistance. This study was supported by NEDO, JST-ALCA, JST-CREST, and Kakenhi. The authors also acknowledge the support of Toyota Motor Corporation. [1] S. Shiraki, H. Oki, Y. Takagi, T. Suzuki, A. Kumatani, R. Shimizu, M. Haruta, T. Ohsawa, Y. Sato, Y. Ikuhara, T. Hitosugi, J. Power Sources 267 (2014) 881-887. [2] M. Haruta, S. Shiraki, T. Suzuki, A. Kumatani, T. Ohsawa, Y. Takagi, R. Shimizu, and T. Hitosugi, Nano Lett. 15 (2015) 1498-1502. Figure 1

Intermetallic Ru2Sn3−δ was found to show high thermoelectric performance of ZT ~ 0.3 at temperatures around 660 K. The transport properties, combined with the electronic structure calculation, indicate that Ru2Sn3 is a semi-metal with contrasting dispersions between the hole and electron bands, which generate a large thermoelectric power of S ~ 100 µV/K. A low thermal conductivity κ of around 1 W m−1 K−1 was observed above room temperature, which is likely due to the strong lattice anharmonicity associated with the martensitic transformation.