M. Tsai

Ionic conductivity in the M2O-P2O5-SiO2 (M=H, Li, Na, K) system prepared by sol-gel methods

Abstract Glasses in the M 2 O-P 2 O 5 -SiO 2 system (M=H, Li, Na, K) were prepared by slowly heating the corresponding sol-gels. Sol-gels were prepared from tetraethylorthosilicate and inorganic reagents. Monolithic samples are obtained when the silica content is greater than 60 mole%. Ionic conductivity was measured by the complex impedance method. For samples of the composition 0.07M 2 O-0.20P 2 O 5 -0.73SiO 2 (M=Li, Na, K) it was found that σ K+ ≥σ Na+ ≥σ Li+ . FTIR data indicate that the gels are phase separated into phosphate rich and silicate rich regions. This is confirmed by EDX. The alkali cations are shown to be located in the phosphate rich regions. Samples prepared by immersing P 2 O 5 -SiO 2 binary monoliths in molten LiCl and allowing to equilibrate under ambient conditions indicate relatively high water content. The highest value of the ionic conductivity measured was 5×10 −2 (ω cm) −1 at 323 K for the composition 0.09P 2 O 5 -0.41SiO 2 -0.33LiCl-0.17H 2 O is attributed to proton motion.

Preparation, characterization and ionic conductivity of (LiCl)2-B2O3-SiO2 xerogels

Abstract (LiCl) 2 -B 2 O 3 -SiO 2 xerogels were prepared by a sol-gel technique. Fourier transform infrared (FTIR) spectra indicate the incorporation of boron into the silica network to form Si-O-B links. 11 B, 7 Li and 29 Si nuclear magnetic resonance (NMR) spectroscopies were used to probe the structure of the xerogels. For a fixed lithium content (10 mol% (LiCl) 2 ), the ionic conductivity of xerogels with B 2 O 3 /SiO 2 ratios of 1/7 to 1/5 is similar to that of lithium chloride, while the conductivity behavior of xerogels with B 2 O 3 /SiO 2 ratios of 1/10 to 1/8 is similar to those of ionically conducting glasses. For samples with the same lithium content, the conductivity increases with decreasing B 2 O 3 /SiO 2 ratio and increasing fraction of BO 4 units (N 4 values). This is attributed to the increasing concentration of lithium ions associated with tetrahedral BO 4 and non-bridging oxygens in the xerogel.

Lithium ion conductivity of sol-gel synthesized LiCl containing ZnOSiO2 xerogels☆

Abstract LiClZnOSiO2 xerogels synthesized by the sol-gel method are shown by powder X-ray diffraction, Fourier transform infrared and 7Li and 29Si NMR spectra to be composites of microcrystalline LiCl and ZnOSiO2 xerogel. Ionic conductivity measurements of the xerogels show extrinsic and intrinsic behavior. Below 280°C, Li+ motion is dominated by a space charge mechanism (significant for 0.40LiCl-0.12ZnO-0.48SiO2), which is indicative of composite character. Above 280°C the conductivity is attributed to the intrinsic conductivity of LiCl in the pores of the xerogel. The increased ionic conductivity with increasing Zn/Si ratio (up to 1 4 ) in the high temperature regime (> 280°C) is ascribed to the decrease of activation energy due to the dissolution of LiCl in the xerogel. The highest Li+ ion conductivity is found to be ∼ 10−3 S/cm at 450°C in the composition 0.40LiCl-0.12ZnO-0.48SiO2, which is half an order of magnitude higher than that of the same composition melt-quenched glass.

Ionic motion in A2In2Mo5O16 [A=Na, K, (Na, Li)] phases

Abstract Ionic conductivity of the three-dimensional network solids A2In2Mo5O16 with A = Na, K was measured by ac impedance. The ionic conductivity of the K analogue, 5 (548 K ) = 7.48 × 10 −7 (ωcm −1 with Ea = 0.63eV is slightly higher than that of the Na isomorph, 5 (548 K ) = 2.38 × 10 −7 (ωcm −1 ) with Ea = 0.79eV . Lithium insertion reactions via n-butyllithium and electrochemically show that ≈one Li/unit formula may be inserted topotactically in Na2In2Mo5O16.

Ionic conductivity in layered Na3Mo2P2O11(OH)·2H2O

Abstract Proton and sodium conductivities of Na 3 Mo 2 P 2 O 11 (OH)·2H 2 O have been studied from 25 to 460°C. The proton conductivity ranged from ∼6×10 −6 S/cm at 26°C to ∼2×10 −5 S/cm at 60°C ( E a =32kJ/mole and and log σ 0 =0.02 S/cm). The profile of proton conductivity as a function of relative humidity is similar to a type III Brunauer adsorption isotherm and suggests that the conduction mechanism is of particle hydrate-type. The proton conductivities at 100°C are ∼5×10 −7 S/cm for RH=6% and ∼9×10 −6 S/cm for RH=100%. Sodium ion conductivity was studied in the dehydrated phase with conductivities σ 267°C ∼2×10 −7 S cm ( E a = 104 kJ mole ) and σ 457° C ∼3×10 −3 S cm ( E a = 208 kJ mole ). The proposed conduction mechanism for sodium ion conductivity is similar to that in Na-β-alumina.