Anisotropic chemical expansion due to oxygen vacancies in perovskite films

Abstract

In scientifically intriguing and technologically important multifunctional ABO3 perovskite oxides, oxygen vacancies are most common defects. They cause lattice expansion and can alter the key functional properties. Here, it is demonstrated that contrary to weak isotropic expansion in bulk samples, oxygen vacancies produce strong anisotropic strain in epitaxial thin films. This anisotropic chemical strain is explained by preferential orientation of elastic dipoles of the vacancies. Elastic interaction of the dipoles with substrate-imposed misfit strain is suggested to define the dipolar orientation. Such elastic behavior of oxygen vacancies is anticipated to be general for perovskite films and have critical impacts on the film synthesis and response functions.

Solution combustion derived oxygen vacancy-rich Co3O4 catalysts for catalytic formaldehyde oxidation at room temperature

“…The lattice expansion of the Co 3 O 4 -SC catalyst was an important indicator of abundant oxygen vacancies. 21 The existence of oxygen vacancies in the Co 3 O 4 -SC catalyst was further corroborated by the Raman spectra as shown in Fig. 4b.…”

Chemical lattice strain in nonstoichiometric oxides: an overview

“…170 Computational methods have been actively employed to elucidate the possible magnitude and nature of defect-induced stresses in thin lms and at surfaces. [171][172][173][174][175][176] For example, the recent ab initio calculations showed that tensile or compressive strain stabilizes oxygen vacancies at complex oxide interfaces. 171 This was explained by the chemical expansion due to the defect formation relieving the stress, 172 and is closely related to the anisotropicin directions parallel and normal to the interfacechemical strain observed with in situ TEM, scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and optical strain measurements in Ce 1-…”

“…172,173 The anisotropic character of chemical expansion was also found in perovskitebased epitaxial thin lms using XRD. 174 Both experimental and computational studies 175,176 showed that the nature of the substrate determines the presence of compressive or tensile inplane strain in perovskite La 1-x Sr x CoO 3Àd lms, which impacts the oxygen vacancy concentration therein, inuencing such properties as the oxygen evolution reaction (OER) activity, 175 oxygen surface exchange and diffusion. 176 Due to the promise of higher efficiency of proton-conducting SOFCs, hydration-induced expansion became the focus of multiple studies, including the computational ones.…”

“…168,[282][283][284] However, in case of thin lms as compared to bulk samples the situation is complicated by anisotropic lattice distortions around oxygen vacancies inherent to many ABO 3 perovskites. 173,174 Elastic interactions of vacancy dipoles with an epitaxial mist strain lead to preferential location of oxygen vacancies in a denite type of atomic plane and, as a result, may cause vacancy ordering, formation of new phases, or phase coexistence/separation. 174 In turn, this may alter the charge transfer properties and cause many other side effects.…”

“…173,174 Elastic interactions of vacancy dipoles with an epitaxial mist strain lead to preferential location of oxygen vacancies in a denite type of atomic plane and, as a result, may cause vacancy ordering, formation of new phases, or phase coexistence/separation. 174 In turn, this may alter the charge transfer properties and cause many other side effects. 173,174,285 To control them, the microscopic nature and elastic behavior of oxygen vacancies in epitaxial lms should be thoroughly studied by both experimental and computational techniques.…”