New A-deficient perovskites in the series LixLa2/3Ti1-xFexO3 (0.12 ≤ x ≤ 0.33) and La(2+x)/3Ti1-xFexO3 (0.5 ≤ x ≤ 1.0)

Two new series of A-deficient perovskites have been synthesized and structurally characterized from Rietveld treatment of their X-ray diffraction powder patterns. The first one, LixLa2/3Ti1-xFexO3, for 0.12 ≤ x ≤ 0.33, results from the substitution mechanism Ti4+ → Fe3+ + Li+. The structure is closely related to that of La2/3-xLi3xTiO3 (a ≈ ap, b ≈ ap and c ≈ 2 ap) with a symmetry evolution leading to the existence of two domains: for 0.12 ≤ x ≤ 0.19 the symmetry is orthorhombic (Pmmm), while for 0.20 ≤ x ≤ 0.33 a tetragonal symmetry is obtained (P4/mmm). In both cases, the population of La3+ ions, unequally distributed on two adjacent sites for smaller x values, is directly affected by the increase of the Li content and tends to be equalized with larger x values. The second series is found to result from another substitution mechanism Ti4+ → Fe3+ + 1/3La3+, leading to the formula La(2+x)/3Ti1-xFexO3 in the domain 0.5 ≤ x ≤ 1.0. The structure is then closely related to that of LaFeO3, where La3+ ions occupy now only one crystallographic site in the Pnma space group. Transmission Electron Microscopy and Mössbauer spectrometry confirm the above models.