Synthesis and ionic conduction of C3A-type nasicon Na3+3x−yY1−xSi3−yPyO9
Abstract In the solid solutions of Na 3+3 x − y Y 1− x Si 3− y P y O 9 , new fast Na + -conductors were obtained. The ionic conductivity, σ, and the activation energy, E , of the most conductive material, Na 4.425 Y 0.375 Si 2.55 P 0.45 O 9 were 5 × 10 −3 S/cm at 300°C and 10 kcal/mol, respectively. Those values were strongly dependent upon the composition. With an increase of Na concentration, [Na], σ increased and E decreased. Accommodation of higher [Na] in the structure was madefeasible by decreasing [Y] and increasing [P]. Based on the crystal structure assumed for Na 3+3 x − y Y 1− x Si 3− y P y O 9 and on the above results, a conduction model was presented. The structural consideration revealed that a conduction path is formed along the 〈1 1 1 〉 direction, where Y 3+ ions locate in the way of Na + ions.