Hiroyuki Kageyama

Conductivity enhancement mechanism of interstitial-type Li+ conductor, Li4 + xBxSi1 − x(0 ≤ × ≤ 0.7)

Abstract An electrical conductivity of σ 100° C = 4.5 × 10 −6 S cm −1 in Li 4.5 B 0.5 Si 0.5 O 4 was observed, which is more than three orders of magnitude higher than that of Li 4 SiO 4 . This enhancement is due to an increase of both the ionic hopping rate and the mobile-ion concentration. An expansion of the crystallographic unit-cell volume of Li 4 + x B x Si 1 − x (0 ≤ × ≤ 0.5) was observed with increasing x . A simple point-charge model calculation shows that the nearest-neighbor Li + ue5f8Li + repulsive force mainly contributes to the expansion of each axis in the unit cell. The conductivity and only the b -axis length among the crystal lattice parameter decreases with x beyond x = 0.5. This results may be interpreted by the application of an BO 4 5− + Li + ⇌ BO 3 − + LiO − equilibrium model.

Ionic conductivity of Li+ ion conductors, Li4.2MxSi1−xO4 (M: B3+, Al3+, Ga3+, Cr3+, Fe3+, Co2+, Ni2+)

Abstract Ionic conductivities of lithium ion conductors, Li4.2MxSi1−xO4, with the trivalent ions. B3+, Al3+, Ga3+, Cr3+, Fe3+, and disvalent ions, Co2+, Ni2+ are discussed in the view of crystal chemistry. The highest conductivity of σ=1.58×10−3 S cm−1 at 300°C was observed in the Al3+ substituted compound. This value is larger by two orders of magnitude than that of Li4SiO4. Refinement of the cell constants for each compound showed that the volume expansion would be attributed to the extra lithium ion content (x=0.2) and MO4 tetrahedron expansion. This may cause the high ionic conductivity, possibly due to the increase of charge carrier concentration.

Li+-ion conductivity of Li1+xMxTi2−x(PO4)3 (M: Sc3+, Y3+)

In Li1+xScxTi2-x(PO4)3 (0<x<0.3), both the conductivity and size of the crystal lattice increase with x, suggesting that Sc3+ ions substitute for Ti4+ ions. In the Li1+xYxTi2-x (PO4)3 system, the ionic conductivity increased with x up to x=0.3, but the crystal lattice did not change with x. EDX analysis of the reaction products prepared by hydrothermal synthesis showed that the Y3+ ions do not substitute for Ti4+ ions. The extra Li+ ions and /or doped Y3+ ions may segregate in the grain-boundary regions, and result in a conductivity enhancement.

Mixed conductivity of Na1+4xMxIIFe2xIIIZr2−3xP3O12, MII: Fe2+, Co2+ and Ni2+

Abstract Zirconium substituted NASICONs, Na 1+4 x M x II Fe 2 x III Zr 2−3 x P 3 O 12 (M II : Fe 2+ , Co 2+ , Ni 2+ ) are obtainable in the range of 0≦ x ≦0.5, which are isostructural to NaZr 2 P 3 O 12 according to powder X-ray patterns. The temperature dependences of the overall electrical conductivities of materials incorporating these three elements with x =0.5 were nearly equal to each other. These materials showed 7×10 −3 S cm −1 at 300°C, and an activation energy of 37 kJ/mol. An electronic conductivity of 5×10 −4 S cm −1 was observed for Na 3 Fe 0.5 II Fe III Zr 0.5 P 3 O 12 at 300°C. However, the electronic conductivity observed for Co 2+ or Ni 2+ substituted materials was very low.

Ionic conductivity of NASICON-type conductors Na1.5M0.5Zr1.5(PO4)3 (M:Al3+, Ga3+, Cr3+, Sc3+, Fe3+, In3+, Yb3+, Y3+)

Abstract Ionic conductivities of Na1.5M0.5Zr1.5P3O12 with trivalent ions Al3+, Ga3+, Cr3+, Sc3+, Fe3+, In3+, Yb3+, Y3+ are discussed in view of material chemistry in the ceramics. The conductivity of Na1.5M0.5Zr1.5P3O12 depended on the ionic radius of the trivalent ion (M3+) substituted for Zr4+ ion in NZP. Estimation of mobile ion concentration (ci) and the mobility (ωp) of Na1.5Ga0.5Zr1.5(PO4)3 and Na1.5Cr0.5Zr1.5(PO4)3 suggests that the conduction mechanisms are different between the grain (bulk) and grain boundary regions.

XAFS study of nasicon-related compounds, Na3Zr0.5Co0.5FeP3O12 and Na3Zr0.5Fe(II)0.5Fe(III)P3O12

The XAFS analyses of the Na + ion conducting Na 3 Zr 0.5 Co 0.5 Co 0.5 FeP 3 O 12 (NCFZP) and mixed-conducting Na 3 Zr 0.5 Fe(II) 0.5 Fe(III)P 3 O 12 (NFZP) are performed at both 60 K and 300 K. The XANES spectra of NCFZP and NFZP at the Zr K-edge show a similar structure to that of the host material NaZr 2 P 3 O 12 (NZP). The Fe K-edge XANES spectrum of NFZP is similar to that of NCFZP, but it contains a parasitic shoulder structure at lower energy. The Zr-O distance of NCFZP and NFZP does not vary from that of NZP, while their Zr-Na distance is significantly shorter that that of NZP. The population of the Na + ion around the doped ions (Co 2+ , Fe 2+ and Fe 3+ ) in NCFZP AND NFZP is increased preferentially as compared with that around the Zr 4+ ion, and distances between the doped ions and Na + are rather shorter than the Zr 4+ -Na + distance of NZP

Enhancement of ionic conductivity of Na4Zr2Si3O12 by the dispersion of SbF5-adsorbed solid superacid particles

Abstract The ionic conductivity ( σ 100°C =1.0×10 −6 S cm) of Na 4 Zr 2 Si 3 O 12 prepared by a conventional solid-state reaction was enhanced by the dispersion of SbF 5 -adsorbed solid superacid particles, SbF 5 / (SiO 2 -Al 2 O 3 ) ( σ 100°C =1.0×10 −4 S cm −1 ), SbF 5 / (SiO 2 -ZrO 2 ) ( σ 100°C =1.3×10 −5 S cm −1 ) and SbF 5 / (TiO 2 −ZrO 2 ) ( σ 100°C =1.3×10 −5 S cm −1 ). The solid superacids were characterized by their acid strength and the concentration of acidic sites on the particle surface. The difference in the conductivity increase is mainly due to the acid strength of the dispersed solid superacid.

Structure of zinc halide-based glasses

Abstract Raman spectroscopic studies on the multicomponent zinc halide-based glasses are summarized and X-ray absorption spectra of the glasses are measured along with zinc halide crystals in order to investigate the structure of the glasses and to obtain the structural parameters. Raman spectra are well explained by a structural model in which the glasses have two types of halides ions, i.e., bridging and non-bridging halide ions, and the glass network is composed of corner-sharing ZnX4 tetrahedra. The X-ray absorption spectra have been analyzed by means of a curve-fitting method using theoretical backscattering amplitudes and phase shifts. Bond distances between zinc and halide ions are shorter than those of the corresponding ZnX2 crystals by 0.01 to 0.02 A. Coordination numbers of the glasses are smaller than those expected from Raman spectroscopy.

EXAFS study on zinc halide glasses

Abstract EXAFS spectra are measured for ZnCl 2 and ZnBr 2 glasses by a laboratory-type X-ray absorption spectrometer. Structural parameters are obtained by a curve fitting method using theoretical phase shifts and backscattering amplitudes. Further, a ‘fine adjustment’ technique proposed by Teo et al. is used to improve the accuracy of the bond distance determination. The results for ZnCl 2 glass are in agreement with the previous study of Desa et al. For ZnBr 2 glass the Zn-Br bond distance was determined to be 2.44 A and the four-fold coordination which has been predicted by Raman spectroscopic studies on ZnBr 2 -based glasses was confirmed.

Ionic conductivity of Na4Zr2Si3O12 dispersed with PZT

Abstract The conductivity of Na 4 Zr 2 Si 3 O 12 (NZS) has been measured containing a ferroelectric dispersant, PZT, to form a composite electrolyte. The variation of conductivity with preparation method, dispersant content and sintering regime has been investigated. NZS made by sol-gel had a lower conductivity than that made by mechanical mixing. At 300°C the maximum conductivities were 4×10 −5 and 4×10 −4 S cm −1 respectively. Adding PZT did not enhance the conductivity at all. Thermal history is the most important factor determining the conductivity.