Trapping of oxygen vacancies in the twin walls of perovskite

Abstract

The binding and pairwise interaction of oxygen vacancies in the ferroelastic ͑100͒ twin walls of the orthorhombic phase of CaTiO 3 perovskite ͑Pbnm͒ have been investigated by numerical simulations using empirical force fields. An oxygen vacancy finds it energetically favorable to reside inside a twin wall, particularly when bridging two titanium ions located in the twin-wall plane. In such case, the binding energy of the vacancy to the wall is 0.7Ϯ 0.1 eV, the error bar reflecting variability within two different force fields. A different disposition of the vacancy in the wall sees its binding energy reduced by a factor of 2. This implies that depending on the relative time scales for twin-wall motion and for oxygen-vacancy diffusion, anelastic motion of twin walls can display two different energy dissipation mechanisms associated to these point defects. The strongest interactions among oxygen vacancies in a twin wall are due to short-range repulsion so that no defect clusters were found. The vacancy-wall binding energy is found to increase substantially with pressure.

Highly mobile vortex structures inside polar twin boundaries in SrTiO3

“…The first and main report of polar interfaces in non-polar materials was in CaTiO 3 : A large spontaneous polarization was predicted in {100} twin walls of CaTiO 3 , a definitely non-polar material. 20 Subsequent experimental studies using transmission electron microscopy 22 and second harmonic generation (SHG) confirmed such wall polarity. 23,24 Similar behavior was attributed to multidomain boundaries with distinct polar and oxygen octahedral tilting in BiFeO 3 ab initio simulations.…”

“…36 The discrepancy, caused by polarization terms, between experimental determination and available classical pair potentials is well known and described elsewhere. 44 Employing standard definitions of octahedral tilting, 7,8,20,45 we found a tilt angle of 9 -11 , formed around each Ti atom in the annealed bulk tetragonal system.…”

Phenomenological thermodynamic potential for CaTiO3single crystals

“…In addition to the strain-induced ferroelectric behavior of thin films, the twin walls of CaTiO 3 have been extensively investigated, including trapping of oxygen vacancies 23,24 , the activation energy for twin-wall motion…”

Diverging Relaxation Times of Domain Wall Motion Indicating Glassy Dynamics in Ferroelastics

“…We also tried to fit the temperature dependence of τ DW with an Arrhenius law, yielding an energy barrier of E a ~ 0.58 eV. This is slightly lower than the value usually found in perovskites for pinning of DW's to oxygen defects 30,31 . However, as clearly seen in Fig.…”