Spark plasma sintering of Al substituted LiHf2(PO4)3 solid electrolytes

Al substituted Li1 + xAlxHf2 − x(PO4)3 (x = 0.0∼0.5) solid electrolytes were prepared by conventional sintering (CS) and spark plasma sintering (SPS), and the Li+ ion conductivity of the sintered pellets was examined using an impedance analyzer. All the samples exhibited a rhombohedral NASICON-type structure. SPS improved the densification compared to CS, and Al substitution further increased the sample density resulting in a maximum density of ∼90%. The Li+ ion conductivity increased in proportion to the sample density and the highest conductivity of 1.1 × 10− 4 Scm− 1 was found in the Li1.5Al0.5Hf1.5(PO4)3 SPS specimen, which is comparable to the best value reported elsewhere. The activation energy of the total conductivity (bulk + grain boundary) reduced from 0.39 to 0.28 eV with Al substitution. The enhanced conductivity was discussed in terms of the densification, bottleneck size, and lithium ion content.