LAUSR

During the last decade solid lithium ion conductors have found widespread applications in areas such as high-energy lithium ion batteries [1-3], electrochemical sensors [4-6] and supercapacitors [7] due to their high ionic conductivity and relatively high chemical stability [8, 9]. Sodium supersonic conductor (NASICON), with a 3D framework structure, is compound as a major fast ionic conduction compound. Various methods for the synthesis of this ceramic compound such as sol-gel [10-12], solid state [13-15] and melt quenching [16-18] process have been used. Sol-gel has several advantages, such as: much lower processing temperatures, a high homogeneity of the resulting structures, the possibility of obtaining pure phase of multicomponent metal oxides [19], low manufacturing cost, simple stoichiometry control, and fast deposition rate [20]. Generally Alkoxides as organometallic reagents [21, 22] or soluble metallic salts (used in Pechini method) [23-25], have applied for sol-gel synthesis of this structure. However, the main disadvantage of alkoxides is their extreme sensitivity to moisture and a high reactivity toward hydrolysis, which affect the hydroxylation process [26]. Pechini process consists of two combined stages; a process of forming metal complexes and in situ polymerization of organic compounds [27]. In general, hydroxycarboxylic acids are used to form stable metal complexes. The polyesterification of metal complexes is reached using a polyhydroxy alcohol and finally a rigid organic polymer is produced. Immobilization of metal complexes in this rigid polymeric network ensures the compositional homogeneity. Thereafter, the polymeric resin is calcinated and a pure phase of multi-component metal oxides is attained [28]. Xu et al. (2007) demonstrated that using citric acid-assisted sol–gel process, it is possible to obtain well crystallized glass-ceramics of Li1.4Al0.4Ti1.6(PO4)3 at a much lower temperature in a shorter synthesis time compared to the conventional solid-state method. They reported that the optimized conditions for citrate-based manufacturing process are: the molar ratio of [citric acid + ethylene glycol] / [Li++Al3++Ti4+] = 4 and pH = 7 [19]. Additionally, Mariappan et al. Abstract: Na super ionic conductive (NASICON) materials are ceramics with three-dimensional scaffolds. In this study, Li1.4Al0.4Ti1.6(PO4)3 with NASICON structure was synthesized by Pechini method. As a result, a sample having a total conduction of 1.18×10-3 S cm-1 was attained. In addition, various parameters were studied to obtain high value of conductivity, by optimizing the process. The optimization was made using L16 Taguchi based orthogonal array, followed by ANOM, ANOVA and stepwise regression. As a result, the optimum synthesis parameters can be obtained, while pH of the solution was adjusted to 7. The ratio between the concentration of citric acid to metal ions and ethylene glycol concentration stuck to 1 and 2.5, respectively. The best heat treatment can be carried out with a combination of pyrolysis at 600 oC and sintering at 1000 oC.