Solid electrolytes based on lithium titanium phosphate were prepared, and their phase, porosity of the sintered pellets, and electrical conductivity were studied. The conductivity was increased and the porosity decreased greatly by partially replacing Ti 4+ and ps+ in LiTi2(PO4)s with M 3 § (M s+ = A1 s+, Cr 3+, Ga 3+, Fe s+, Sc s+, In 3+, Lu s § y3+, and La 3+) and Si 4+ ions, respectively. The maximum conductivity at 298 K is 7 • 10 -4 S cm-' for Lil.sM0.3Ti,.7(PO4)s (M = A1 and Sc). The conductivity was considerably increased by the mixing of binders such as Li20 or Li4P207 with LiTi2(PO4)s. The main reason for the conductivity enhancement of these electrolytes seems to be attributable to the increase of the sintered pellet density with the enhancement of the lithium concentration at the grain boundaries.

Ionic conductivities have been investigated for lanthanoid silicates of the Lnlo(Si04)603 solid solution series and related compounds. The activation energy and conductivity at 500 "C were estimated to be 69 kJ mol-' and 1.8 x S cm-' for Lalo(Si04),03 and 71 kJ mol-' and 1.5 x ~O -~ Scm-' for Ndlo(Si04),03. The a and c lattice constants of the hexagonal phase decreased with decreasing radius of the Ln3+ ion for Lnl0(SiO4),O3 (Ln = La, Nd, Sm, Gd and Dy). The activation energy increased and the conductivity decreased when Ln3+ ions with smaller ionic radii were used. The sole carrier in these materials is the 0'ion.

The all‐solid, lithium rechargeable battery, which if available would find many applications, is one reason for carrying out research into Li⊕‐conducting solids. Fast Li⊕‐conducting ceramic electrolytes are reviewed with regard to their electrical properties and crystal structure. Both non‐oxide based ceramics and oxide materials are considered, and possibilities for further developments—e.g., the preparation of the electrolyte by thin film techniques—are pointed out.