Mechanisms of the effect of dopants and P(O(2)) on the improper ferroelastic phase transition in SrTiO(3)

作者：Tkach Alexander; Vilarinho Paula M^*; Kholkin Andrei L; Reaney Ian M; Pokorny Jan; Petzelt Jan

来源：Chemistry of Materials, 2007, 19(26): 6471-6477.

DOI：10.1021/cm071795c

Perovskite-structured SrTiO(3) 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 La(3+) and Mn(2+) A-site substitution and Mn(4+) and Mg(2+) B-site substitution in polycrystalline SrTiO(3) processed in air and sintering SrTi(0.95)Mn(0.05)O(3-delta) in different P(O(2)) has been studied using in situ Raman spectroscopy and electron diffraction. The transition temperature was raised when Mn(2+) and La (3+) were substituted for Sr(2+) but lowered for Mn(4+) and Mg(2+) substitution on the Ti site. Sintering SrTi(0.95)Mn(0.05)O(3-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 SrTi(0.95)Mn(0.05)O(3-delta) in low P(O(2)) and (ii) adjustment of the perovskite tolerance factor (t) when, e.g., La(3+) (1.36 angstrom) and Mn(2+) (1.27 angstrom) substitute for Sr(2+) (1.44 angstrom, decrease in t) and Mn(4+) (0.53 angstrom) substitutes for Ti(4+) (0.605 angstrom, increase in t).

• 出版日期2007-12-25