Crystal structure of the mixed conductors phases, Li0.5-3xLa0.5+x+yTi1-3yM3yO3 (M = Mn, Cr) with x = 0.133 and y = 0.20

Perovskite-like solid solutions of general formula Li0.5-3xLa0.5+x+yTi1-3yM 3yO3 (M = Mn, Cr) show three polymorphs; A, beta and C. The crystal structu re of the C polymorphs in manganese- and chromium-lanthanum systems, determ ined from powder neutron diffraction using Rietveld refinement, are of the ordered perovskite type. The structures of both phases are similar, contain ing a three dimensional framework of corner-sharing MO6 (M = Ti or Mn/Cr) o ctahedra in which the structures are partially collapsed as a result of a c ooperative tilting and rotation of octahedra. Orthorhombic unit cell, M = M n: a = 5.5411 (11) Angstrom, b = 7.8120(14) Angstrom, c = 5.4924(10) Angstr om; M = Cr: a = 5.5014(9) Angstrom, b = 7.7735(15) Angstrom, c = 5.4729(9) Angstrom; space group Pnma (no. 62). Ionic conductivity takes place by a ho pping mechanism between Li+-occupied and empty A-sites, while electronic co nductivity is along octahedra.