Effect of oxygen vacancies on electronic states of CaVO3- delta and SrVO3- delta : A photoemission study

The Role of Phonons and Oxygen Vacancies in Non-Cubic SrVO3

Combining neutron diffraction with pair distribution function analysis, we have uncovered hidden reduced symmetry in the correlated metallic d¹ perovskite, SrVO₃. Specifically, we show that both the local and global structures are better described using a GdFeO₃ distorted (orthorhombic) model as opposed to the ideal cubic ABO₃ perovskite type. Recent reports of imaginary phonon frequencies in the density functional theory (DFT)-calculated phonon dispersion for cubic SrVO₃ suggest a possible origin of this observed non-cubicity. Namely, the imaginary frequencies computed could indicate that the cubic crystal structure is unstable at T = 0 K. However, our DFT calculations provide compelling evidence that point defects in the form of oxygen vacancies, and not an observable symmetry breaking associated with calculated imaginary frequencies, primarily result in the observed non-cubicity of SrVO₃. These experimental and computational results are broadly impactful because they reach into the thin-film and theoretical communities who have shown that SrVO₃ is a technologically viable transparent conducting oxide material and have used SrVO₃ to develop theoretical methods, respectively.

Oxygen Vacancy Linear Clustering in a Perovskite Oxide

Oxygen vacancies have been implicitly assumed isolated ones, and understanding oxide materials possibly containing oxygen vacancies remains elusive within the scheme of the isolated vacancies, although the oxygen vacancies have been playing a decisive role in oxide materials. Here, we report the presence of oxygen vacancy linear clusters and their orientation along a specific crystallographic direction in SrTiO₃, a representative of a perovskite oxide. The presence of the linear clusters and associated electron localization was revealed by an electronic structure represented in the increase in the Ti²⁺ valence state or corresponding Ti 3d² electronic configuration along with divacancy cluster model analysis and transport measurement. The orientation of the linear clusters along the [001] direction in perovskite SrTiO₃ was verified by further X-ray diffuse scattering analysis. Because SrTiO₃ is an archetypical perovskite oxide, the vacancy linear clustering with the specific aligned direction and electron localization can be extended to a wide variety of the perovskite oxides.

Mutual experimental and theoretical validation of bulk photoemission spectra of Sr1-xCaxVO3

We report high-resolution high-energy photoemission spectra together with parameter-free LDA + DMFT (local density approximation + dynamical mean-field theory) results for Sr1-xCaxVO3, a prototype 3d(1) system. In contrast to earlier investigations the bulk spectra are found to be insensitive to x. The good agreement between experiment and theory confirms the bulk sensitivity of the high-energy photoemission spectra.