Processing and electrical conductivity property of lithium-doped high-entropy pyrochlore and perovskite ceramics

Lithium-doped Li0.66La1.12(Ti0.2Zr0.2Hf0.2Sn0.2Nb0.2)2O7 (LLTNO), Li0.66La1.12(Ti0.2Zr0.2Hf0.2Sn0.2Ta0.2)2O7 (LLTTO) high-entropy pyrochlore and Li0.5Sr0.5(Ti0.2Zr0.2Hf0.2Sn0.2Ta0.2)O3 (LSTTO), Li0.5Ba0.5(Ti0.2Zr0.2Hf0.2Sn0.2Nb0.2)O3 (LBTNO) high-entropy perovskite ceramics were synthesized by solid state reaction method and sintered. Crystal structure, microstructure and electrical properties of these high entropy ceramics were studied. The LLTNO and LLTTO pellets sintered at 1300 °C present a pyrochlore structure, while LSTTO and LBTNO pellets sintered at 1350 °C present a perovskite structure. The LBTNO ceramics has a total conductivity of 1.25 × 10−7 S•cm−1 at room temperature while the LSTTO sample exhibits the highest conductivity of 2.11 × 10−7 S•cm−1 among all samples. Both LSTTO and LBTNO ceramics present negligible electronic conductivity. Relative densities of the LLTNO, LLTTO, LSTTO and LBTNO ceramics were 82, 88, 86 and 87%TD, respectively, which is the reason for low conductivity of these high entropy ceramics. The activation energies of the LSTTO and LBTNO samples were 0.39 and 0.38 eV, respectively, which is close to the traditional Li+-type conducting solid electrolytes.