Mechanisms of the effect of dopants and P(O-2) on the improper ferroelastic phase transition in SrTiO3


Perovskite-structured SrTiO3 undergoes a cubic (Pm3m) to tetragonal (I4/mcm) transition at similar to 108 K (T-a) associated with rotations of the O octahedra in the antiphase around the [001] direction. This phase transition gives rise to modes at the R point of the Brillouin zone in the Raman spectra and superlattice reflections at 1/2(odd-odd-odd}. The effect on T-a of La3+ and Mn2+ A-site substitution and Mn4+ and Mg2+ B-site substitution in polycrystalline SrTiO3 processed in air and sintering SrTi0.95Mn0.05O3-delta in different P(O-2) has been studied using in situ Raman spectroscopy and electron diffraction. The transition temperature was raised when Mn2+ and La (3+) were substituted for Sr2+ but lowered for Mn4+ and Mg2+ substitution on the Ti site. Sintering SrTi0.95Mn0.05O3-delta in N-2 reduced T-a, but sintering in O-2 had a negligible effect compared to air. It is proposed that two mechanisms are responsible for the modification of T-a: (i) the creation of oxygen vacancies by acceptor doping (Mg 2+ ions on the Ti site) and sinterin SrTi0.95Mn0.05O3-delta in low P(O-2) and (ii) adjustment of the perovskite tolerance factor (t) when, e.g., La3+ (1.36 angstrom) and Mn2+ (1.27 angstrom) substitute for Sr2+ (1.44 angstrom, decrease in t) and Mn4+ (0.53 angstrom) substitutes for Ti4+ (0.605 angstrom, increase in t).




Chemistry; Materials Science


Tkach, A; Vilarinho, PM; Kholkin, AL; Reaney, IM; Pokorny, J; Petzelt, J

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