The Role of Phonons and Oxygen Vacancies in Non-Cubic SrVO.

Combining neutron diffraction with pair distribution function analysis, we have uncovered hidden reduced symmetry in the correlated metallic perovskite, SrVO. Specifically, we show that both the local and global structures are better described using a GdFeO distorted (orthorhombic) model as opposed to the ideal cubic ABO perovskite type. Recent reports of imaginary phonon frequencies in the density functional theory (DFT)-calculated phonon dispersion for cubic SrVO 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 SrVO. These experimental and computational results are broadly impactful because they reach into the thin-film and theoretical communities who have shown that SrVO is a technologically viable transparent conducting oxide material and have used SrVO to develop theoretical methods, respectively.