Lithium-ion conduction in mixed-metal phosphates, (LiMMIII)-M-V(PO,), [M-V
= Nb, Ta; M-III = Al, Cr, Fe], possessing the rhombohedral (R (3) over bar
c) NASICON structure has been investigated. Among the phosphates investigat
ed, LiTaAl(PO4)(3) exhibits the highest conductivity, sigma approximate to
1.0 x 10(-2) S cm(-1) at 350 degrees C (E-a = 0.47 eV), comparable to the c
onductivity of LiTi2(PO4)(3). Unlike LiTi2(PO4)(3) which contains lithium-r
educible Ti-IV, LiTaAl(PO4)(3) contains stable Ta-V and Al-III oxidation st
ates and hence deserves further attention towards tailoring new lithium-ion
conductors for application as electrolytes in solid state lithium batterie
s.