The detailed crystal structure of cubic Li7La3Zr2O12 has been successfully determined by single-crystal X-ray structure analysis. The three-dimensional network of the Li-ion migration pathway with short Li–Li distance and occupational disordering is formed in the garnet-type framework structure. The basic unit of the pathway can be expressed as a loop constructed by the Li1 and Li2 sites. The loop links to another one, where only the Li1 site is shared by two loops as a junction.

ABSTRACT:A new iron-based superconductor (Ca,Pr)FeAs 2 was discovered. Plate-like crystals of the new phase were obtained and crystal structure was investigated by single-crystal X-ray diffraction analysis. The structure was identified as the monoclinic system with space group P2 1 /m, and is composed of two Ca(Pr) planes, anti-fluorite Fe 2 As 2 layers, and As 2 zigzag chain layers. Plate-like crystals composed of the new phase showed superconductivity with T c ~20 K in both magnetization and resistivity measurements.Several groups of iron-based superconductors, such as REFeAs(O,F) 1 (RE = rare earth elements), AEFeAsF 2 (AE = alkaline earth metals), AEFe 2 As 2 3 , LiFeAs 4 , FeSe 5 , and compounds having perovskite-type oxide layer (ex. Fe 2 P 2 Sr 4 Sc 2 O 6 6 ) have been discovered since 2008. Developments of superconducting tapes and wires have been already attempted for potassium doped AEFe 2 As 2 and fluorine doped REFeAsO, because of their high T c and high H c2 . On the other hand, discovery of new superconductor with high T c and high chemical stability has been still desirable. Since iron-based superconductors are composed of stacking of superconducting layers of Fe 2 Pn 2 or Fe 2 Ch 2 ) (Pn = P, As, Ch = S, Se, Te) and blocking layers, design and search of new blocking layers are promising for discovery of new superconductors. There are several compounds having anti-fluorite blocks and As-based blocks such as UCuAs 2 7 . Recently new iron based superconductors Ca 10 (Pt 3 As 8 )(Fe 2 As 2 ) 5 and Ca 10 (Pt 4 As 8 )(Fe 2 As 2 ) 5 8-10 were reported. These compounds have As-based blocking layers between Fe 2 As 2 layers. The structures of these compounds indicate that there are possibilities to find new iron-based superconductors with arsenide blocking layers. In addition, Saha et al. reported that single crystalline (Ca,RE)Fe 2 As 2 (RE = La, Ce, Pr, Nd) showed superconductivity with high T c exceeding 40 K in resistivity measurement 11 . After this report, superconductivity in RE-doped CaFe 2 As 2 has been reported by several groups 12 . On the other hand, there are several works that report coexistence of two superconducting phases or interface superconductivity in this system 13,14 . Therefore, new superconducting phase is expected in Ca-RE-Fe-As system.In the present study, we have explored new iron-based superconductors in Ca-Pr-Fe-As system and found a new compound (Ca,Pr)FeAs 2 . We report a crystal structure and physical properties of (Ca,Pr)FeAs 2 .All samples were synthesized by the solid-state reaction starting from FeAs(3N), PrAs(3N), Ca(2N), As(4N), and CaO(3N). Since the starting reagents, PrAs and Ca are sensitive to moisture and/or oxygen in air, manipulations were carried out in an argon-filled glove box. Powder mixtures were pelletized, sealed in evacuated quartz ampoules, and reacted at 1000~1200°C for 24 h. Constituent phases were studied by the powder XRD measurements using RIGAKU Ultima-IV diffractometer and intensity date were collected in the 2 range of 5°-80° at a step of 0....

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Today, all-solid-state secondary lithium-ion batteries have attracted attention in research and development all over the world as a next-generation energy storage device. A key material for the all-solid-state lithium batteries is inorganic solid electrolyte, including oxide and sulfide materials. Among the oxide electrolytes, garnet-type oxide exhibits the highest lithium-ion conductivity and a wide electrochemical potential window. However, they have major problems for practical realization. One of the major problems is an internal short-circuit in charging and discharging. In the polycrystalline garnet-type oxide electrolyte, dendrites of lithium metal easily grow through the void or impurity in grain boundaries of the sintered body, which causes serious internal short-circuits in the battery system. To solve these problems, we present an all-solid-state battery system using a single-crystal oxide electrolyte. We are the first to successfully grow centimeter-sized single crystals of garnet-type by the floating zone method. The single-crystal solid electrolyte exhibits an extremely high lithium-ion conductivity of 10−3 S cm−1 at 298 K. The garnet-type single-crystal electrolyte has an advantageous bulk nature to realize the bulk conductivity without grain boundaries such as in a sintered polycrystalline body, and will be a game-changing technology for achieving highly safe advanced battery systems.

Li2Ti6O13 was prepared from Na2Ti6O13 as a parent compound via sodium/lithium ion exchange in molten LiNO3 at 380 °C. It crystallizes in the monoclinic system, space group C2/m, and with the lattice parameters of a = 15.3065(4) Å, b = 3.74739(8) Å, c = 9.1404(2) Å, and β = 99.379(2)°. The crystal structure of Li2Ti6O13 was refined to the conventional values of R wp = 5.78% and R p = 4.44% with a fit indicator of GOF = R wp/R e = 1.66 by Rietveld analysis using powder neutron diffraction data. The crystal structure of Na2Ti6O13 was also reinvestigated using the single-crystal X-ray diffraction data with the final R value of 2.70%. The basic (Ti6O13)2− framework in Li2Ti6O13 was maintained nearly unchanged from that in the parent Na2Ti6O13. The Li occupation site in the tunnel space shifted to y = 0.5 position from the original Na site in Na2Ti6O13, and the moving resulted in the LiO4 planar coordination in Li2Ti6O13. The structural stability of Li2Ti6O13 was confirmed by bond valence sums, the data of 7Li-MAS NMR and high-temperature in situ XRD measurements, and the results of the present first-principles calculation by the FLAPW method. The electrochemical Li insertion/extraction experiments revealed the irreversible large Li insertion capacity of above 200 mAh g−1 at approximately 1.5 V for the first cycle and the stable reversible capacity of approximately 90−95 mAh g−1 during the following cycles. The total Li-ion conductivity in Li2Ti6O13 was estimated to be σtotal = 5.60 × 10−6 S cm−1 at room temperature from the results of AC-impedance measurements. This value is comparable to that in the well-known good Li-ion conducting ramsdellite-type Li2Ti3O7.

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