Nobuhito Imanaka

Ionic Conductivity of Solid Electrolytes Based on Lithium Titanium Phosphate

Solid electrolytes based on lithium titanium phosphate were prepared, and their phase, porosity of the sintered pellets, and electrical conductivity were studied. The conductivity was increased and the porosity decreased greatly by partially replacing Ti4+ and P5+ in with M3+ and Si4+ions, respectively. The maximum conductivity at 298 K is for . The conductivity was considerably increased by the mixing of binders such as or with . The main reason for the conductivity enhancement of these electrolytes seems to be attributable to the increase of the sintered pellet density with the enhancement of the lithium concentration at the grain boundaries.

Ionic conductivity of the lithium titanium phosphate (Li/sub 1+x/M/sub x/Ti/sub 2-x/(PO/sub 4/)/sub 3/, M=Al, Sc, Y, and La) systems

High lithium ionic conductivity was obtained in Li/sub 1+X/M/sub X/Ti/sub 2-X/(PO/sub 4/)/sub 3/ (M=Al, Sc, Y, and La) systems. Lithium titanium phosphate, LiTi/sub 2/(PO/sub 4/)/sub 3/, is composed of both TiO/sub 6/ octahedra and PO/sub 4/ tetrahedra, which are linked by corners to form a three dimensional network, with a space group R3-barC. Some workers have already described that the conductivity increased considerably if Ti/sup 4+/ in LiTi/sub 2/(PO/sub 4/)/sub 3/ was substituted by slightly larger cations such as Ga/sup 3+/(1),Sc/sup 3+/(2), and In/sup 3+/(3,4). These results are similar to each other because of their close ionic radii. In this communication, substitution effects of Ti/sup 4+/ in LiTi/sub 2/(PO/sub 4/)/sub 3/ by various ions (Al/sup 3+/, Sc/sup 3+/, Y/sup 3+/, and La/sup 3+/) on their conductivities are reported.

Electrical property and sinterability of LiTi2(PO4)3 mixed with lithium salt (Li3PO4 or Li3BO3)

Abstract A lithium salt (Li 3 PO 4 or Li 3 BO 3 ) was added to LiTi 2 (PO 4 ) 3 to obtain a dense pellet of the phosphate. The porosity of the sintered pellets decreased and the conductivity was enhanced by the utilization of a binder. A maximum conductivity of 3.0 × 10 −4 S·cm −1 at 298 K was obtained for a sample of LiTi 2 (PO 4 ) 3 −0.2Li 3 BO 3 . The activation energy for the lithium migration at grain boundaries was decreased by the addition of lithium salt. The reason for the conductivity enhancement was attributed to a decrease in the activation energy for the lithium migration at the grain boundary and an increase in the contact area between grains. The conductivity of the bulk component was also increased by the enhancement of Li + -ion migration at grain boundaries.

Ionic conductivity and sinterability of lithium titanium phosphate system

Abstract Lithium titanium phosphates mixed with various metal ions of M 3+ (M=Al, Cr, Ga, Fe, Sc, In, Lu, Y, or La), Li 1+ x M x Ti 2− x (PO 4 ) 3 systems, were prepared, and their properties were investigated. The conductiv ity was enhanced and the porosity of the sintered pellets decreased by the partial replacement of Ti 4+ with the M 3+ ion. The porosity was considerably influenced by the ionic radius of the M 3+ ion. The sinterability was greatly related to the increase of lithium concentrations at the grain boundary. The conductivity enhancement by the substitution mainly resulted from the densification of the sintered pellets.

The Electrical Properties of Ceramic Electrolytes for LiM x Ti2 − x ( PO 4 ) 3 + yLi2 O , M = Ge , Sn , Hf , and Zr Systems

The electrical properties of systems of , were examined in detail. The conductivity and the sinterability increased with the amount of excess lithium oxide in the phosphate. The secondary phase acts as a flux to accelerate the sintering process and to obtain high conductivity grain boundaries. The conductivity decreased and the activation energy of the bulk component for Li+ migration increased by the partial substitution of Tr4+for M4+ in systems of . A minimum activation energy of 0.28–0.30 eV, was obtained for the sample with ca. 1310 A3 in the cell volume. has the most suitable tunnel size for a Li+ migration through the NASICON‐type network structure.

Electrical properties and crystal structure of solid electrolyte based on lithium hafnium phosphate LiHf2(PO4)3

Abstract The electrical properties and the crystal structure were investigated for the ceramic electrolytes based on LiHf 2 (PO 4 ) 3 . The conductivity enhanced by the Li 2 O addition with LiHf 2 (PO 4 ) 3 system and by the increase of x for Li 1+ x M x Hf 2− x (PO 4 ) 3 (M=Cr, Fe, Sc, In, Lu or Y) systems. The P2 1 /n monoclinic phase transformed to NASICON-type R 3 c rhombohedral phase at above 1173 K. The activation energy for Li + ion migration was decreased by the phase transition. The activation energy for bulk component was 0.42 eV for the NASICON-type structure. A maximum conductivity at 298 K is 1.7 × 10 −4 S·cm −1 for the sample of Li 1.2 Fe 0.2 Hf 1.8 (PO 4 ) 3 .

Total oxidation of toluene on Pt/CeO2–ZrO2–Bi2O3/γ-Al2O3 catalysts prepared in the presence of polyvinyl pyrrolidone

Pt/CeO(2)-ZrO(2)-Bi(2)O(3)/gamma-Al(2)O(3) (Pt/CZB/Al(2)O(3)) catalysts for the catalytic combustion of toluene, which is one of the volatile organic compounds (VOCs), were prepared by the wet impregnation method in the presence of polyvinyl pyrrolidone (PVP). X-ray powder diffraction, transmission electron microscopy, and BET specific surface area measurement using N(2) adsorption have been used to characterize the catalysts. The catalytic test was conducted from room temperature in a flow of 900 ppm of toluene in air and gas hourly space velocity (GHSV) of 8000 h(-1). The catalytic activity was evaluated in terms of C(7)H(8) conversion and the gas composition after the reaction was analyzed using two gas chromatographs with a flame ionization detector (FID) and a thermal conductivity detector (TCD). The Pt/CZB/Al(2)O(3) catalysts are specific for the total toluene oxidation and CO and any toluene-derivative compounds were not detected as by-products. The specific surface area of the catalysts was increased by the addition of PVP in the preparation process. By the optimization of the amount of platinum, complete oxidation of toluene was realized at a temperature as low as 120 degrees C on a 7 wt%Pt/16 wt%Ce(0.64)Zr(0.15)Bi(0.21)O(1.895)/gamma-Al(2)O(3) catalyst.

Rare earth contribution in solid state electrolytes, especially in the chemical sensor field

Abstract In solid state electrolytes, rare earths are commonly used, and a number of their properties are exploited in these applications. Firstly, the rare earth can be utilized as a dopant to produce the mobile ion vacancies in an electrolyte and to enhance the ionic conducting characteristics. Secondly, they can be used as the principal constituent of the electrolytes. In both these case, the characteristics that the rare earths hold a stable trivalent state even though the main ionic mobility is via mono- or trivalent ions. Thirdly, the rare earth trivalent ion alone can migrate in some solids. This unexpected feature has been recently clarified by selecting the appropriate structure for the trivalent ion conduction in order to reduce the electrostatic interaction between the mobile ions and the framework of the solid. In solid electrolytes, only one ionic species can migrate. This feature is very advantageous for chemical sensor applications, especially from the viewpoint of selective and quantitative detection of specific gas species. The rare earth contribution to solid state electrolytes has been rapidly increasing, and has been expanding further the realms of application not only in the industrial field but also in the whole science field. Here, the rare earths contribution to the solid state electrolyte field is briefly reviewed.

Synthesis and luminescence of Sr2CeO4 fine particles

Fine particles of a blue emission phosphor Sr{sub 2}CeO{sub 4} have been synthesized using a chemical co-precipitation technique, and the textual and luminescent properties were compared with the one synthesized by the conventional solid-state reaction method. Particle size and distribution of the Sr{sub 2}CeO{sub 4} fine powder prepared by the co-precipitation process were smaller and narrower than those obtained by the samples prepared from the conventional one. The emission intensity of the fine particles was equal to that of the larger particles prepared from the solid-state reaction, on the contrary to the general tendency that emission intensity decrease with particle size reduction. Although no Ce{sup 3+} peaks were observed in EPR measurements, X-ray photoelectron spectra of the samples clearly elucidated the existence of Ce{sup 3+} only on the surface of Sr{sub 2}CeO{sub 4}.

Thermal contraction behavior in Al2(WO4)3 single crystal

Abstract The anisotropic thermal expansion behavior of a single crystal of Al 2 (WO 4 ) 3 was obtained for the first time and the anisotropic contraction behavior was identified. The direct clarification of the anisotropic behavior contributes greatly towards designing the thermal expansion characteristics along every axis, realizing unique materials such as a zero expansion material.