Lao.67-~Li3xTiO3 solid solution forms in the range ~0.15 > x > ~0.04 by the substitution mechanism La ~ 3Li. Superstructure reflections observed in this range are consistent with a superlattice consisting of the stacking of two perovskite subcells. A line-splitting phenomenon observed for x < ~0.1 indicates that the tetragonal distortion of the cubic perovskite subcell occurs. The solid solutions exhibit high lithium ion conductivities greater than 10 4 S cm -~ at room temperature in a wide range, x> ~0.04. A maximum conductivity of 1.1 • 10 _3 S cm -~ is found at x = 0.1. The dome-shaped composition dependence of conductivity indicates that the conduction mechanism involves the movement of lithium ions through the A-site vacancies.Lithium ion-conducting materials have attained great prominence in the last decade because of their potential applications for electrolytes in high energy batteries and other electrochemical devices. 1 Several oxides are known to exhibit high lithium ion conductivity; 2 most conductive materials are 3,~-Li3PO4-type solid solutions, 3 (Li-Na) 13-alumina, 4 and lithium-substituted Na superionic conductors (NASICONs). 5 In general, oxide materials are superior to nonoxide materials such as Li3N and Lil-based glasses for chemical and electrochemical stability and mechanical properties] '4 However, one major problem with the practical applications, except for low power applications, still remains in the unavailability of lithium solid electrolytes with high conductivity.Perovskites of the type ABe3 may be regarded as a 3-dimensional framework structure constructed from vertex-sharing Be6 octahedra and A ions placed in 12-coordinate sites in the cubic
The authors have fabricated a field-effect transistor (FET) based on a rutile TiO2 active channel. Top-gate transistor structure with an amorphous LaAlO3 insulator was fabricated on the ultrasmoothed rutile single crystals. Reproducible n-type FET actions were observed only by the use of ultrasmoothed TiO2 surfaces. Moreover, an anisotropy of the field-effect mobility depending on the channel direction, which reflects intrinsic nature of rutile, was definitely observed. Inserting MgO insulating buffer between TiO2 and amorphous LaAlO3 suppressed the off-state current and realized on-to-off current ratio as high as 104.
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