Formation of perovskite solid solutions and lithium-ion conductivity in the compositions, Li2xSr1−2xMIII0.5−xTa0.5+xO3 (M = Cr, Fe, Co, Al, Ga, In, Y)

Formation of solid solutions with perovskite structure and ionic conductivity have been investigated in the systems Li2xSr1−2xMIII0.5−xTa0.5+xO3 (M = Cr, Fe, Co, Al, Ga, In, Y). Perovskite solid solutions formed in ranges of x ≤ 0.25 for M = Fe, Cr, x < 0.22 for Ga and x < not, vert, similar 0.16 for M = Co, In. No single-phase samples of perovskite solid solution were prepared for M = Al, Y. The solid solutions Li0.5Sr0.5MIII0.25Ta0.75O3 (M = Fe, Cr; x = 0.25) had high bulk conductivities of 1.0 × 10−4 S cm−1 and 6.0 × 10−5 S cm−1 at room temperature, respectively. The former value was the highest of those reported to date for lithium electrolytes based on tantalates. They were simple cubic perovskites (space group: Pm3m; a = 396.39 pm for Fe, a = 395.03 pm for Cr), indicating that the Li and Sr ions, and the M (Fe or Cr) and Ta ions are randomly distributed over the A-sites and B-sites, respectively. Frame emission analysis for Li in both sintered pellets revealed that the loss of the Li content took place during sintering. The high conductivity is probably attributed to an A-site deficient perovskite phase resulting from the loss. The perovskite solid solutions in the other systems exhibited conductivities as low as 10−7–10−8 S cm−1. The Fe- and Cr-containing solid solutions are the first of tantalate-based perovskites with high Li-ion conductivity.