Sodium Ion Mobility in Triple Molybdate Na 25 Cs 8 Sc 5 (MoO 4 ) 24

Cationic transport in triple molybdate Na 25 Cs 8 Sc 5 (MoO 4 ) 24 with an alluaudite structure has been studied. According to 23 Na NMR, the ion jump frequency is as high as τ _d^-1 10 4 ‒10 5 s –1 at Т = 550‒600 K, and the activation energy for sodium diffusion is E a 0.9 eV. The mobility of Na + ions is slower than that found in double molybdate Na 5 Sc(MoO 4 ) 4 , which is caused by structural features. In Na 25 Cs 8 Sc 5 (MoO 4 ) 24 , some of sodium positions are replaced by Cs + ions preventing the sodium diffusion in a channel along the c axis. As a result, the 2D mechanism of Na + transport typical of the Na 5 R(MoO 4 ) 4 alluaudite family does not occur. The most probable mechanism of sodium diffusion in Na 25 Cs 8 Sc 5 (MoO 4 ) 24 involves successive atomic jumps along a zigzag path in the ab plane.