Mechanisms of the Effect of Dopants and P(O2) on the Improper Ferroelastic Phase Transition in SrTiO3

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• 作者：Alexander Tkach ; Paula M. Vilarinho ; Andrei L. Kholkin ; Ian M. Reaney ; Jan Pokorny ; Jan Petzelt
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：December 25, 2007
• 年：2007
• 卷：19
• 期：26
• 页码：6471 - 6477
• 全文大小：1303K
• 年卷期：v.19,no.26(December 25, 2007)
• ISSN：1520-5002

文摘

Perovskite-structured SrTiO₃ undergoes a cubic (Pm3m) to tetragonal (I4/mcm) transition at ~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 SrTi_0.95Mn_0.05O_3–δ in different P(O₂) has been studied using in situ Raman spectroscopy and electron diffraction. The transition temperature was raised when Mn²⁺ and La³⁺ were substituted for Sr²⁺ but lowered for Mn⁴⁺ and Mg²⁺ substitution on the Ti site. Sintering SrTi_0.95Mn_0.05O_3–δ in N₂ reduced T_a, but sintering in O₂ 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 (Mg²⁺ ions on the Ti site) and sintering SrTi_0.95Mn_0.05O_3–δ in low P(O₂) and (ii) adjustment of the perovskite tolerance factor (t) when, e.g., La³⁺ (1.36 Å) and Mn²⁺ (1.27 Å) substitute for Sr²⁺ (1.44 Å, decrease in t) and Mn⁴⁺ (0.53 Å) substitutes for Ti⁴⁺ (0.605 Å, increase in t).