Synthesis and Na⁺conduction properties of the ceramics of Na₅YSi₄O₁₂-type phosphate-substituted solid solutions

The Na⁺-superionic conducting ceramics with Na₅YSi₄O₁₂-type structure were synthesized using the composition formula of Na_3+3x−yY_1-xP_ySi_3-yO₉, in which some portions of Na⁺ions are considered to replace Y³⁺as Na_{(13+8x−4y/3)}[Na_(4x−1)/3Y_(4–4x)/3] [P_4y/3Si_(12–4y)/3]O₁₂according to Na₅YSi₄O₁₂-type composition formula. The average ionic radius of the 6-coordinated Y³⁺sites [= (4x− 1)/ 3 ×r_Na+ (4 - 4x)/3 ×r_Y] approximately covered the range ofr_Gdand tor_Sm. The ionic conduction properties were strongly dependent upon the combination of composition parameters,xandy. In this report, the dependence of conduction properties on the composition is discussed on the basis of structural considerations.